Sanitary Engineer

Very amazing software used for drawing longtidunal sections (profiles)

2011-05-25T14:47:00.000-07:00

Pipe2CAD is an AutoCAD add-on which can be used efficiently to complete the design work of pipe networks, such as water supply, sanitary sewer, and storm drainage networks.

After finishing the hydraulic design of your pipe networks with any of the available hydraulic design packages, networks are easily imported into Pipe2CAD environment to proceed with all subsequent design steps. From checking interference points and conflicts between different networks, verification of low and high points in pressure networks, and editing networks by adding, deleting, or adjusting pipes; to finally producing fully formatted plan views and longitudinal profiles, ready for submission.

http://www.zshare.net/download/898408932e533826/

For any questions don’t hesitate to ask me

Design of Sewers part 2

2011-05-25T14:17:00.000-07:00

Sewer Appurtenances

Sewer appurtenances are the various accessories on the sewerage system and are necessary for the efficient operation of the system. They include man holes, lamp holes, street inlets, catch basins, inverted siphons, and so on.

Man-holes: Man holes are the openings of either circular or rectangular in shape constructed on the alignment of a sewer line to enable a person to enter the sewer for inspection, cleaning and flushing. They serve as ventilators for sewers, by the provisions of perforated man-hole covers. Also they facilitate the laying of sewer lines in convenient length.

Man-holes are provided at all junctions of two or more sewers, whenever diameter of sewer changes, whenever direction of sewer line changes and when sewers of different elevations join together.

Special Man-holes:

Junction chambers: Man-hole constructed at the intersection of two large sewers.

Drop man-hole: When the difference in elevation of the invert levels of the incoming and outgoing sewers of the man-hole is more than 60 cm, the interception is made by dropping the incoming sewer vertically outside and then it is jointed to the man-hole chamber.

Flushing man-holes: They are located at the head of a sewer to flush out the deposits in the sewer with water.

Lamp-holes: Lamp holes are the openings constructed on the straight sewer lines between two man-holes which are far apart and permit the insertion of a lamp into the sewer to find out obstructions if any inside the sewers from the next man-hole.

Street inlets: Street inlets are the openings through which storm water is admitted and conveyed to the storm sewer or combined sewer. The inlets are located by the sides of pavement with maximum spacing of 30 m.

Catch Basins: Catch basins are small settling chambers of diameter 60 - 90 cm and 60 - 75 cm deep, which are constructed below the street inlets. They interrupt the velocity of storm water entering through the inlets and allow grit, sand, debris and so on to settle in the basin, instead of allowing them to enter into the sewers.

Inverted siphons: These are depressed portions of sewers, which flow full under pressure more than the atmospheric pressure due to flow line being below the hydraulic grade line. They are constructed when a sewer crosses a stream or deep cut or road or railway line. To clean the siphon pipe sluice valve is opened, thus increasing the head causing flow. Due to increased velocity deposits of siphon pipe are washed into the sump, from where they are removed.

Pumping of Sewage

Pumping of sewage is required when it is not possible to have a gravitational flow for the entire sewerage project.

Sufficient pumping capacity has to be provided to meet the peak flow, atleast 50% as stand by.

Types of pumps :
Centrifugal pumps either axial, mixed and radial flow.
Pneumatic ejector pumps.

Design of Sewers part 1

2011-05-25T14:08:00.000-07:00

Design of Sewers

The hydraulic design of sewers and drains, which means finding out their sections and gradients, is generally carried out on the same lines as that of the water supply pipes. However, there are two major differences between characteristics of flows in sewers and water supply pipes. They are:
The sewage contain particles in suspension, the heavier of which may settle down at the bottom of the sewers, as and when the flow velocity reduces, resulting in the clogging of sewers. To avoid silting of sewers, it is necessary that the sewer pipes be laid at such a gradient, as to generate self cleansing velocities at different possible discharges.
The sewer pipes carry sewage as gravity conduits, and are therefore laid at a continuous gradient in the downward direction upto the outfall point, from where it will be lifted up, treated and disposed of.

Hazen-William's formula

   U=0.85 C rH0.63S0.54

Manning's formula

   U=1/n rH2/3S1/2

where, U= velocity, m/s; rH= hydraulic radius,m; S= slope, C= Hazen-William's coefficient, and n = Manning's coefficient.

Darcy-Weisbach formula

   hL=(fLU2)/(2gd)

Minimum Velocity

The flow velocity in the sewers should be such that the suspended materials in sewage do not get silted up; i.e. the velocity should be such as to cause automatic self-cleansing effect. The generation of such a minimum self cleansing velocity in the sewer, atleast once a day, is important, because if certain deposition takes place and is not removed, it will obstruct free flow, causing further deposition and finally leading to the complete blocking of the sewer.

Maximum Velocity

The smooth interior surface of a sewer pipe gets scoured due to continuous abrasion caused by the suspended solids present in sewage. It is, therefore, necessary to limit the maximum velocity in the sewer pipe. This limiting or non-scouring velocity will mainly depend upon the material of the sewer.

Effects of Flow Variation on Velocity in a Sewer

Due to variation in discharge, the depth of flow varies, and hence the hydraulic mean depth (r) varies. Due to the change in the hydraulic mean depth, the flow velocity (which depends directly on r2/3) gets affected from time to time. It is necessary to check the sewer for maintaining a minimum velocity of about 0.45 m/s at the time of minimum flow (assumed to be 1/3rd of average flow). The designer should also ensure that a velocity of 0.9 m/s is developed atleast at the time of maximum flow and preferably during the average flow periods also. Moreover, care should be taken to see that at the time of maximum flow, the velocity generated does not exceed the scouring value.

2011-05-25T08:42:00.000-07:00

WORLD’S LARGEST WATER TREATMENT PLANT OPTIMIZES PROCEDURES BASED ON ALGOR FLUID FLOW RESULTS

Nearly one billion gallons of water are processed on an average day at James W. Jardine Water Purification Plant, which is located next to Navy Pier in Chicago, Illinois. This plant and the South Water Purification Plant serve nearly 5 million consumers in the City of Chicago and 118 outlying suburbs. Engineers at the plant are using ALGOR’s complete suite of simulation tools to formulate modifications that improve the water purification process.

Nearly one billion gallons of water are processed on an average day at the James W. Jardine Water Purification Plant in Chicago, Illinois, the largest water treatment plant in the world. This plant and the South Water Purification Plant serve nearly 5 million consumers in the City of Chicago and 118 outlying suburbs. With that volume of water to purify, the chemical treatment process must be as efficient and effective as possible. Recently, the Jardine plant needed to change the location at which activated carbon is added in order to increase its contact time with water. Engineers at the plant studied the water flow patterns in the intake area with ALGOR’s Fluid Flow Analysis software to find the optimal feed point at which to add the carbon so that dispersion time would be minimized.

Approaching this challenge with computer simulation tools diverges from the water industry’s standard practice of building scale models and performing tests in a laboratory. The use of ALGOR’s Fluid Flow Analysis software enabled water plant engineers to determine the best location for the activated carbon feed point in less time and with less expense than would have been possible with a traditional, laboratory testing approach.

The First Step in a Seven-Hour Water Purification Process

There are a number of steps in the 7-hour water purification process, which consists of chemical treatment with activated carbon, polyphosphate, chlorine, fluoride, alum (aluminum sulfate) and polyelectrolyte, followed by sedimentation and filtration. Each chemical additive serves a different purpose, such as killing bacteria, aiding in the removal of micro-organisms or preventing tooth decay. Activated carbon is the first chemical treatment, added to remove objectionable tastes and odors. The tiny carbon particles are tremendously absorbent, like a sponge. In order for it to do its job, the activated carbon must mix thoroughly within the water for as long as possible.

Adding activated carbon to lake water is the first step of many in the 7-hour water purification process. The diagram above shows a generalized, schematic view of the process used by the City of Chicago Department of Water to purify Lake Michigan water. Activated carbon is used to remove objectionable tastes and odors and must mix thoroughly within the water for as long as possible in order to be effective.

In the late 1990s, engineers for the City of Chicago Department of Water determined that the activated carbon feed should be moved to the intake basins through which lake water enters the plant. Each spring, plant workers drain and clean each of the two intake basins. Water plant workers have only a short window of time each year to clean the basins and make any needed modifications. The activated carbon feed line was extended and mounted on the inside wall of each intake basin, over a small ledge – a location that was selected for installation convenience.

This modification achieved the goal of increasing contact time that the carbon has with the water. Next, Department of Water Filtration Engineer Anthony Wietrzak, Ph.D., P.E. turned his attention to the challenge of optimizing the dispersion and mixing of carbon within the water. This challenge required Wietrzak to study the hydraulics of the water flow within the intake basin.

“The water industry’s standard practice for approaching such a problem is to build a scale model and perform tests in a laboratory,” said Wietrzak. “Unfortunately, this process is time-consuming and expensive. Chicago’s Bureau of Water Treatment engineering section at the Jardine Water Purification Plant acquired ALGOR’s Professional Multiphysics software package several years ago to provide computer simulation tools for just such a challenge.” In addition to the unsteady laminar fluid flow analysis capabilities Wietrzak would use for this project, the Professional Multiphysics package also offers static stress with linear and nonlinear material models, Mechanical Event Simulation with linear and nonlinear material models, steady and unsteady laminar fluid flow analysis with turbulence, steady-state and transient heat transfer analysis, electrostatic analysis, vibration analysis and the capability to consider the effects of multiple physical phenomena.

Pump Cells Analyzed to Determine Inputs for the Intake Basin Model

To analyze the flow pattern within the intake basin, Wietrzak had to start with the physical characteristic of the system that he knew quantitatively: the capacity of each of the pumps that pulls water from the intake basin into the water treatment plant and the physical dimensions of the intake area. Wietrzak did not want to assume that the flow was uniform coming out of the intake basin. That assumption could result in an unrealistic flow pattern within the intake basin. Thus, he would have to model the pump cells in addition to the intake basin. However, modeling both the pump cells and the intake basin would result in a very large model. Wietrzak was concerned that his computer hardware would not process such a large model and achieve solution convergence in a reasonable amount of time. Therefore, Wietrzak decided to model and analyze one pump cell and the intake basin separately. The pump cell model results at the boundary between the intake basin and the pump cell would determine the input for the intake basin model.

Wietrzak began by modeling the volume within a pump cell in Superdraw III, ALGOR’s precision finite element model building tool. The pump cell model resulted in 6,492 solid “brick” elements. Wietrzak applied zero velocity constraints to the surfaces on the walls of the pump cell. To the free surface at the top of the pump cell, he applied a zero shear constraint. Next, Wietrzak converted the pump capacity of 300 million gallons per day to a volumetric flow rate in feet per second. The flow rate was then applied to the pump cell outlet as a velocity boundary constraint. No constraints were placed on the inlet to the pump cell.

An unsteady fluid flow analysis was performed on the pump cell model with the applied velocities ramping up over 50 time steps. Performing an unsteady fluid flow analysis and ramping up the velocities over time facilitated convergence.

Wietrzak first analyzed one of the pump cells that pulls water out of the intake basin and into the water treatment plant. The known pump capacity was used as the input to the analysis in order to find the velocity profile at the inlet to the pump cell. The sketch shows where the water enters and exits the pump cell (upper left) while the velocity contour resulting from the ALGOR fluid flow analysis shows the fluid dynamics within the volume of the pump cell.

“The largest assumption I made for the pump cell model is that the flow is uniform coming out of the pump,” said Wietrzak. “I ran several variations of the pump cell model in which I varied the outlet velocity constraints at the pump discharge and none made a significant difference in the velocity profile at the inlet to the pump cell. All models yielded higher velocities at the top of the entrance and lower velocities near the bottom. Since I was concerned only with the velocity profile boundary condition at the outlet of the basin (which is also the inlet to the pump cell), I am satisfied that this is a sensible assumption.”

Running several variations on the pump cell model gave Wietrzak the opportunity to experiment with different model constraint techniques and gauge the effectiveness of those techniques in terms of model convergence. “I know the theory and how to handle problems with a textbook approach. However, there were several constraint techniques that I needed to learn in order to run this model and get realistic results,” said Wietrzak, who holds a Ph.D. in fluid dynamics from Northwestern University. “For example, the free surface boundary condition had to be properly applied in order to get the solution to converge. ALGOR’s technical support team was very helpful in answering any questions that arose during the solution process.”

Intake Basin Model Reveals the Need to Change Activated Carbon Feed Point

Armed with the results of the pump cell fluid flow analysis, Wietrzak was ready to tackle the intake basin model. He began by modeling the volume within the basin in Superdraw III, a model which resulted in 8,138 solid “brick” elements. As with the pump cell model, Wietrzak applied zero velocity constraints to the surfaces on the walls of the basin and zero shear constraints to the free surface. The velocity results of the pump cell analysis were then applied to the area where the basin connects to the pump cells. An unsteady fluid flow analysis was performed on the intake basin model with the applied velocities ramping up over 50 time steps.

The simulated velocity profile at the inlet to the pump cell was applied to the intake basin model. The sketch shows where the water enters and exits the intake basin (upper left); the location of the original activated carbon feed point (Add Point 1); and the location of the new feed point based on analysis results (Add Point 2). The velocity contour resulting from the ALGOR fluid flow analysis shows the fluid dynamics within the volume of the intake basin.

Wietrzak then studied the simulated flow patterns by slicing through the model layer by layer and viewing the flow patterns throughout the model. He also used animated analysis replays to see how the solution progressed over time. He discovered a recirculation pattern next to the wall, very near to the current feed point. “The feed point is located above a narrow ledge,” describes Wietrzak. “The flow pattern predicted that the carbon would tend to be dragged along the ledge rather than mixing quickly and thoroughly with water throughout the volume of the basin. Our observations of the carbon deposits qualitatively confirmed the fluid flow analysis results.”

Wietrzak therefore determined that the activated carbon feed pipe should be moved out between 5 and 10 feet from the wall in order to maximize mixing. This modification was implemented in one of the two intake basins in the Spring of 2000.

Wietrzak has also used the ALGOR Multiphysics package to model other areas of the plant that may benefit from modifications. For example, since completing the activated carbon feed point project, Wietrzak has studied the effectiveness of the air scrubber system on exchanging the air in the chlorine battery room, from where chlorine is supplied for the treatment process. The scrubber releases caustic gas to neutralize airborne chlorine. Wietrzak used fluid flow analysis to find the “dead spots” in the air flow.

“We do not redesign everything, but ALGOR’s complete suite of simulation tools is enabling us to formulate modifications that improve the water purification process,” said Wietrzak. “The variety of simulation tools offered by the Professional Multiphysics package will enable us to study many phenomena on the computer and make many enhancements without the need for laboratory testing.”

Sewage Water Treatment

2011-05-25T08:33:00.001-07:00

There are many Chemical Physical and Biological methods for treatment of aqueous waste waters. Most combination of these chemical, Physical and biological treatments is necessary to remove contaminants effectively.

The method has to be determined based on the requirement of the waste water and its contaminants.

Simple Household Sewer Treatment

Septic system: Though simple but very important system covering rural and urban areas in most of the developed and under developing countries.

Septic systems are constituted of number pipe lines by which the house hold aqueous waste water is drained to a series of tanks which are connected by pipe lines. The first tank is connected to inlet line and the last to outlet.

The septic tank has two chambers usually each with manhole and separated by a wall that has opening on the roof and floor of the tank.

The household waste water enters the first chamber of the first tank; at this point, the solids settle to the bottom and the scum floats to the top. The solids are settled and digested, which lessens the content of the tank. The remaining liquid flows through the dividing wall and into the second chamber. Here, further settlement takes place so that the excess liquid becomes nearly clear and empties into the drainage field, also known as the leech field. The remaining impurities of the water are then broken down into the soil and taken to irrigate plants around.

Conventional Municipal Waste Water Treatment

2011-05-25T08:32:00.000-07:00

Conventional municipal waste-water treatment, preliminary steps include, screening to remove large solids. Grit removal to protect mechanical equipment against abrasive wear

Flow measuring and pumping to lift the waste water.
Primary treatment is to remove settle able organic matter accounting to percent of suspended solids and scum.
Secondary treatment is by aeration in open basins with return biological solids or fixed media followed by final setting excess microbial growth settled out in the final clarifier is wasted while the supernatant is disinfected with chlorine prior to discharge to a receiving water course.
Waste sludge’s from primary settling and secondary biological flocculation are thickened and dewatered for preparation to disposal.
Anaerobic bacterial digestion may be used to stabilize the sludge prior to dewatering.
The overall process of conventional waste water treatment` can be viewed as, thickening: to percent depending upon the plant Solvents moved from solution are concentrated in a small volume convenient for final disposal.
The contribution of raw sanitary waste water is about gallons per person with a total solid content of 0.1 percent.
240mgs/l suspended solids.
200 mgs of B.O.D
Liquid waste sludge is withdrawn from primary and secondary processing amounts to approximately 2l/persons with a solids content of 5 percent by weight.
This is further concentrated to handle able material by mechanical dewatering, the extracted water is returned for reprocessing. Cake , amounts to about 1/3l/l with a 30 percent solid concentration from vacuum filter which is used in large plants to extract water directly from raw sludge.
This type of physical -biological scheme is effective in reducing the organic content of waste water and the main objective is maximum reduction of suspended solids and BOD

Sewage Definition

2011-05-25T08:30:00.000-07:00

Sewage water is generated from domestic, factories and agricultural activities. Domestic waste water is called as sewage

Sources of sewage

waste water from kitchen and bathroom is called gray-water or sullage

waste water from toilet is called excreta or black- water

Sewage water consists of 99.3 to 99.7 % of liquid state and 0.3 to 0.7% of solids state.

The solids present in the sewage water are of two types

Organic solids
Inorganic solids.

Organic solids are the substances derived from living things like produces from plant and animal. The organic solids undergo decomposition by the microorganisms.

Examples : carbohydrate, protein & fat.

Inorganic solids are inert materials that they do not undergo decomposition by the microorganisms and are inert fixed solids.

Examples: Grit, Salt, Chemicals, Metals etc.

These two states are mainly degradation of the environment if they are discharged into the environment as such.

If these solids are removed from the sewage water by Treatment process the water can be reclaimed and reused.

Composition of Sewage

How Much Does a New Septic System Cost?

2011-05-25T08:22:00.000-07:00

One of the biggest disadvantages of septic systems is that they do not come in standard sizes and prices. You cannot just walk into a shop, point to one and say, “I will take that one. How much for it?” Rather you have the difficult task of doing a bit of research and then coming to an estimate of the price that you would have to pay for septic system. Further, the estimate may not be accurate and you may have pay additional money. Here we give you a handy guide on what all the factors are that you should consider when deciding on a new septic system cost.
Septic system cost varies depending on a number of different factors, such as, the area where you live, the type and quality of the septic system that you want installed, the material costs, not only of the septic system, but the fees applicable in your area, and finally the labor charges of the company that will actually install the septic system for you. Regional differences in cost are one of the largest factors in price variation in an installation. In some states and regions of the US you can get a septic system installed for $3,000- $5,000, but in other regions it will cost much more. For example, one of my friends in Massachusetts had to pay close to $15,000 for his!
Another factor is the material used in the construction of the septic tank. Tanks made of concrete are cheaper than ones made out of high-density polyethylene. However, the disadvantage is that concrete tanks do not last as long. Aerobic septic systems cost even more because they requireseptic tank alarms and sometimes lift-pumps.

New Septic System Cost Estimates

One of the very first actual costs will be the official permits that you will need. You will have to pay for permits to be allowed to install the septic tank. Calling your local Town Hall and inquiring about that should provide you with an idea about the fees involved.
You should start off by asking your friends and neighbors about the price that they had to pay for their septic systems. Ask them about the companies that they used, the quality of the service and construction that those companies provided. One of the other most important sources is your local realtors. They are in the business and have an idea about the prices that companies charge to install various fixtures, including septic tanks. They often have to install septic tanks in houses before re-selling them; they are your best bet for professional and non-partisan advice.

Maintenance Costs of a New Septic System

Typical costs for the annual maintenance of septic systems, the drain field and of mound septic systems range from $30 to $500. Depending on your location, $500 may not even be the upper end of the range. Usually costs are this high only if you must replace pumps and other fittings, which itself happens only once every few years or decades. The standard gravity-fed tank and trench systems generally need to be inspected and pumped every 1-3 years. The normal septic tank pumping cost is about $75-$350. For septic systems with sand and peat filters or with wetlands construction, the annual costs range between $50 and $1,700, depending on the monitoring requirements and discharge methods.
A typical septic system lasts for decades, on average about 20-40 years. Throughout this time, some will need their pumps and other fixtures replaced and/or repaired. New septic system costs can vary greatly. The maintenance costs of a septic tank are dependant not only the tank itself, but also on the care and educated management with which it is treated. A new home owner should educate themselves on the proper care of a septic system in order to benefit from the least expensive and most trouble-free system possible.

What is Septic Seep?

2011-05-25T08:20:00.000-07:00

The process of septic seeping was invented in 1953 in the laboratory of Chevron-Ortho by wastewater and soils specialists. Septic Seep is a chemical that arrives in your drain field and interacts with the soils to reduce the occurrence of hardpan soil situations. Septic Seep mechanism of action is similar to that enzymes and bacteria, but there are no enzymes or bacteria in the product. The active ingredient is Calcium Polysulfide.
The system has gained a lot of acclaim among thousands of customers who have installed and used it with positive results. If you think you might need to replace your drain field try Septic Seep first because it is much more affordable and can potentially solve your problem. For an average home with 3 occupants and 2 bathrooms, the septic system can process around 85,000 gallons of wastewater per year. The wastewater is passed from the septic tank into the septic drain field where bacteria inhabitating the soils will purify the greywater.
In regards to your septic tank, you will have set some firm rules in your household. For instance, you will create problems when using chemicals such as sodium detergents, cleaning soaps and water softeners. These chemicals will cause clay debris in the soil to tightly bond making it impermeable to water. You will also encounter a problem when expelling to much grease. The grease will form a tar-like layer known as Biomat. When the layer thickens, it becomes an impermeable barrier that stops water absorption in the soil resulting into soil floods. The problems continue to multiply when the Biomat kills the helpful bacteria leaving the water to flood the drain field surface (this is called septic tank failure). According to the manufacturers of Septic Seep, their product will fix all of the above problems in many cases.

Using Septic Seep In Your Home

It is simple to use a septic seep in your septic system. A average septic system will use at least half a gallon ofSeptic Seep every 6 months. All you have to do is pour Septic Seep down a sink drain or flush it down the toilet. If your septic system has been neglected (no septic tank emptying) in recent memory, then it is recommend that you use a full gallon of Septic Seep in the first round of treatment and later on use two cups for every week for a month. Then reduce the dose to 1 cup per week indefinitely to keep your system running without problems. For seepage and cesspools pits, half a gallon is enough for the first treatment followed by 1 cup per every pit for two consecutive weeks.
Some crystallization will occur in Septic Seep that has been stored for extended periods of time. The product is still good. All you have to do is break up the crystals, mix with water and flush down the drain. In the septic tank, the crystals will fully dissolve and Septic Seep will go to the drain field where it will treat the soil.
If Septic Seep sounds like it may help you then I encourage you to visit their website for more information.

How to Properly Pump Your Septic Tank

2011-05-25T08:18:00.001-07:00

As a matter of hygiene, septic tanks need to be clean and well-maintained at all times; however, there are many people who do not care much about this important responsibility. One of the most important steps towards a well-maintained septic system is learning how to pump your septic tank; or better yet, how to find the phone number of the septic contractor that will empty the system for you.

A lot of the material that is sent to your septic tanks stays at the bottom of the tank in the form of sludge. If the septic tank is not cleaned for a considerable duration of time, the septic tank can overflow or back up into your house. You should empty your septic tank every 1 to 3 years, depending on how many people live your household and how big the tank is. The septic tank pumping cost is a few hundred dollars. If you do not have septic risers installed the costs may be even higher because the contractor will have to do extra work.
There are chemicals on the market that can speed up the digestion of organic matter in your septic tank, but they are not a replacement for emptying the tank. They may however, allow you to wait longer between cleaning. Feel free to learn more about these septic tank cleaners.

When learning how to pump your septic tank you will quickly learn that when disposing your waste products, not everything should be put down the drain. For example, grease, insecticides, sanitary products, oils, paints and tampons should never be flushed down the toilet or the sink. Even food from a food-disposal systems should not be used unless you have a sewage grinder pump installed. Only human excrement are recommended for draining because that is what septic systems are designed to handle. Review the septic tank diagram for a quick refresher on the design of these systems.
Cleaning a full septic tank is not an easy task; there are specially designed tools used for this purpose; most notably, the septic tank pumping truck. Pumping the septic tanks is the most effective method of cleaning as it removes any trace of sludge, mud, and debris remnants that usually prevent your system from functioning properly. To make sure your septic tank maintains a healthy flow, proper pumping of the tank should be practiced every 1 to 3 years. To make sure you are doing thing rights, you may ask for assistance from your local health officers. They will provide you with necessary information on how to properly pump your septic tank and how often it should be done.
A good habit to develop is inspecting your septic system from time to time. By so doing you will make sure cracked pipes and leaks are detected and repaired early before they cause major problems. Qualified contractors can conduct septic tank inspections for you and they are readily available via the phone book and the internet. If the problem is something you can manage without calling contractors, you can go ahead and save yourself the time and inspection fee before letting in the health personnel to come and conduct their own check up.
One of the best ways to save money on your septic tank maintenance is learning about how to pump septic tanks. That way you will know what is and what is not allowed to enter your septic tank.

How Do I Remove Tree Roots From My Sewer Lines?

2011-05-25T08:17:00.001-07:00

There are many benefits to be gained from trees once they are planted in the right location. On the other hand, if they are located near sewer lines they will become more of a nuisance than anything else; tree roots and sewer lines don’t mix. Tree roots are excellent at locating water and will travel several feet to locate the nourishment they need. Upon locating the sewer line, which for them is a steady water source, they will cause problems for the entire sewer system. If neglected you will need to hire a plumber or get the roots out the system. As with most things, an ounce of prevention is better than a pound of cure. Prevent the problem from the beginning rather than try to fix it after it has happened.

Problem Solving When Tree Roots and Sewer Lines DO Mix

Most plumbers will suggest that you snake the drainpipe to remove as many roots as possible. Following that, apply a solution of copper sulfate to prevent roots from growing in again. You can find copper sulfate crystals in feed store’s and hardware stores. Simply spread the crystals in the soil around the sewer lines and roots will be discouraged. Sometimes just finding the sewer lines can be too difficult for the average homeowner. If that’s the case for you then I suggest hiring a plumber to help you find them.

Picture showing tree roots in a sewer line. The tree roots were left unchecked and broke the pipe.

Once the line has been located, remove the plug and pour the copper sulfate solution into it. Make the solution using hot water which will melt the crystals faster. It will require several applications to see results. Most plumbers recommend that the solution be reapplied every four months in a long-term effort to prevent root growth. Another option is to use a foaming copper sultfate agent which will completely coat the insides of the sewer lines.
We all know that trees ‘drink’ through their roots; however, when they find their way to the sewer line then they will create serious issues. To prevent this from happening and still allowing trees to find alternate water sources to live on you will need to encourage the roots to look elsewhere. Copper sulfate is one of the safest ways of doing just that, but don’t over do it. You don’t want to contaminate the drinking water of animals or humans with too much copper sulfate. Whenever you are planning to plant a tree, just remember, tree roots and sewer lines don’t mix.

There Are Two Types of Septic Tank Diagram

2011-05-25T08:16:00.000-07:00

When someone wants to have a septic tank diagram they mean one of two things. Either a map of where your septic tank is located on your property or technical diagram describing and showing the parts of a septic system.

Let’s talk a little more about the first one: the map.

Why do we even want a map to our septic tank? If you’re like most people, you know what aseptic tank smells like and you would rather it stay buried in the ground so you can’t see it or smell it. Well, here are some reasons why you may want to keep a septic tank diagram in a safe place.

During a septic tank inspection the inspector will need to locate the septic tank. If you have a map, it’s easy. However, if you do not have a map then the inspector has to find the tank and that will cost you extra.
If you want to save yourself a few dollars you could do your own septic tank maintenance, but only if you know where the septic tank is.
You want to extend your driveway, so you unknowingly pave right on over your septic tank and septic drainfield. Big mistake, since that eliminates access and encourages septic tank failure because those components are not designed withstand such weight.

I could go on, but I think you catch my drift: you need a septic tank diagram showing you where the tank and the drain field are located!

Below is an example of a map showing the where the septic components are located.

Now let’s talk about the second kind of septic tank diagram: the technical drawing.

The picture below is a example of a septic tank drawing. Most septic tanks are buried in the ground, they are made of either plastic, fiberglass or, most commonly, concrete and they are water tight.

Water enters the septic tank from the house plumbing through the Inlet Tee. The solids that enter with the water sink to the bottom forming the "sludge" and the grease and oil floats to the surface forming the "scum". The remaining wastewater, also called greywater, exits from the Outlet Tee and makes it way to the septic drain field.

The purpose of the technical septic tank diagram is to help the homeowner understand how their septic system works. If it is a diagram that the contractor who installed the tank gave you then it will probably tell you the volume of the septic tank, how far the drainfield is from the tank, what the tank is made of, etc.

If you are buying a house then you should request to have a copy of the septic tank diagram. The realtor or the previous owner of the house should have one on hand. If not, then a septic tank diagram can be drawn up for a fee.

Detecting a Septic Tank Alarm False Alarm

2011-05-25T08:12:00.000-07:00

it is recommended that any septic system that moves septic effluent from a septic tank to a drain field has a septic tank alarm in place. The alarm should be located in your house so that if it does sound, you will be able to hear it.
If you recently moved into a newly built home there is a chance that there is a septic tank alarm installed already. If you hear a beeping/buzzing sound or a red light flashing somewhere in your home, your basement or in your yard it may be indicated that your septic tank pump is malfunctioning.
The alarm sounds when septic effluent (wastewater) is not being pumped to the drain field. When you hear or see the alarm, you should call a septic tank pumping company immediately to avoid the septic effluent backing up into your house. The septic tank pumping cost is much lower than the cost of renovating a basement that was destroyed by septic effluent.

Septic Tank Alarm Schematic

There is more than one situation that can cause aseptic tank alarm to sound. If you know what the reasons are then you may be able to save yourself a lot of work and some money.

The power may have been disconnected from the septic tank pump by accident
Are you properly maintaining your septic tank pump – a septic tank pump will usually last only 10-15 years
It may be possible that the lines in your septic tank drain field are clogged, causing the water to back up and not drain properly
Is your septic tank pumped out on a regular basis (every 1-3 years)?
Was there a power outage in your area that could have created a false alarm?

Never ignore the septic tank alarm because it could result in septic tank failure and a septic effluent backing up into your house. That is never a good situation. If you do not yet have a septic tank alarm installed on your septic tank system look into getting one. It can save you a lot of time, a lot of backbreaking labor and costly repairs.
Below you will find listings for septic tank alarms over at Amazon.com. The prices range between $50 USD and $400 USD. I encourage you to visit Amazon just to read the reviews of each product so that you can make a more informed decision when you decide to buy.

2011-05-25T08:07:00.000-07:00

Septic Tank Risers – The Ultimate Back Savers

if you are new to septic tanks you may wonder what a septic tank riser is. A septic tank riser is essentially a connection between the septic tank and the surface of your yard. Septic tanks are usually buried a few feet underground for health and safety reasons. Tucking them underground also prevents the spread of septic odors. Having a septic riser installed allows your tank to be buried a few feet underground while still allowing easy access for when it needs to be pumped, maintained or inspected. I have had the unfortunate experience of needing my septic tank pumped, before I had a septic riser installed. It took me a few hours to dig down to the top of the septic tank and that was the easy part. I then had to find location the septic tank lid, so I kept digging around and eventually I found it. I had the guy who pumped my septic tank install a riser the next day. Now that I have the riser installed future pumpings will be a lot less work for me.
Septic tank risers come in three different materials: concrete, PVC, and polyethylene.

Concrete Septic Tank Riser

The concrete septic tank riser is probably the cheapest kind and is also one of the most difficult to install because of its weight. The lid is also made of solid concrete and it is too heavy and cumbersome to remove each time the tank has to be inspected or pumped. Depending on your landscaping the concrete septic tank riser may be hard to look at, unless your backyard is entirely concrete. Concrete risers have also been known to leak and decompose over the years. The disadvantages clearly outweigh the benefits and for this reason people tend to avoid concrete septic tank risers.

Polyethylene Septic Tank Riser

The polyethylene septic tank risers are quite popular; however, it is difficult to seal the connection between the riser and the concrete septic tank. This is can cause all kinds of problems if your septic tank ended up over flowing.

PVC Septic Tank Riser

That brings us to our third choice: the PVC septic tank riser. This type is the most popular, it is easy to install, light weight and the edges are designed to make a tight seal with the septic tank’s surface. The only drawback is that it can cost a pretty penny; you get what you pay for.

PVC Septic Tank Riser

The type of septic tank riser you select is personal preference and you will want to select a type that somehow fits into your landscaping. If you have a lot of concrete in your landscaping then a concrete lid sticking out of the ground would not be such a big deal. You do also have the option of covering the lid completely with something aesthetic like gravel or paving tile. Keep in mind that the lid will have to be uncovered when a septic tank is pumped so do not place anything permanent on top of the septic tank riser.
As I mentioned earlier, after I dug out my septic tank lid, a septic tank servicing company came and pumped my septic tank. While they were there, I had them install a septic tank riser (PVC) at the same time. It took them about 10 minutes to install the riser, seeing as I had already done all the back-breaking labor by digging the septic tankvout, the riser was really no problem. If you want to install a septic tank riser and money is an issue keep in mind that the septic tank contractors do charge quite a hefty hourly wage. In my case it was not so expensive because I spent the hours digging, they did not.
There are some places where having a septic tank riser is a legal requirement, so if you live in those areas then the contractor who installed the septic tank probably installed the riser as well. Another advantage of having a septic riser is that you know exactly where your septic tank is.
Even if the septic tank riser is not required in your area I strongly recommend that you have one installed because they make your life a lot easier. Perhaps not easier in the sense of “everyday life” but when things go wrong they tend to go wrong at the worst possible time and during the worst possible you do not want to be in the backyard for hours digging a hole in the dirt.

2011-05-25T08:01:00.000-07:00

What Is A Sewage Grinder Pump and Do You Need One?

A sewage grinder pump is an important device used in many homes to aid in waste management. Sewage pump grinders help with the disposal of everything sent to the septic tank through sinks, bathtubs, showers, and toilets. The wastewater from all the appliances makes its way through the pipes and connects into the grinder pump storage system. Once a certain level of waste is in the grinder it will activate and grind the waste into fine slurry and pump it into the main septic system.

On the market today are the most commonly used sewage grinder pumps: the Centrifugal Grinder Pump and the Semi-Positive Displacement (SPD). What makes up a grinder pump system is the tank, the grinder/pump and the alarm panel. For most households, a pump having 1 to 2 horsepower is plenty. The grinder pump has sensors built in and attached on the exterior. The sensors detect how full the grinder pump tank is and if there are problems with the system.Homeowners they do not have too worry much about their sewage grinder pump malfunctioning allowing the waste to overflow because the sensors will detect it before it is a problem. The homeowner will then be alerted via the alarm panel and they can then fix the problem or call a septic system contractor to fix it.

Depending on the manufacturer, the materials used in manufacturing grinder holding tanks can vary but the most common types are constructed from high-density polyethylene (HDPE), fiberglass or fiberglass reinforced polyester (FRP). All makes of sewage grinder pumps have an opening that serves as an inlet for the waste and a discharge outlet leading to the main septic tank. If you are installing this system into an existing house there is very good chance that you will have to modify the plumbing in order to incorporate a sewage grinder pump. There are also grinders that are large enough to be able to service multiple homes which are all connected to one grinder pump station and one septic tank system.

Advantages of a Sewage Grinder Pump

By grinding up the waste the surface area is increased which means that the bacteria and enzymes in the septic tank will be able to decompose the waste more quickly and efficiently. This may lead to fewer septic tank pumping calls. The alarm system for the alarm is a big advantage because you will be alerted to any problems so you do not have to constantly check the system. If you have a food-disposal unit in your kitchen sink (not recommended for normal septic tank setups) then the food will go through an additional grinding cycle making it easier to process.
As a final note, although sewage grinder pumps help a lot you still cannot send harmful chemicals down your drains; for example, sanitary products, kitty litter, oils, paints, etc.

2011-05-25T07:53:00.000-07:00

Aerobic Septic System

Aerobic septic systems are not the same as standard septic systems because they use aerobic bacteria where as standard septic systems use anaerobic bacteria. Aerobic bacteria require oxygen and can work much faster than anaerobic bacteria, which means that they can dispose of more effluent in less time and therefore require less space. Another difference between the two septic systems is that the aerobic system requires electricity and therefore requires regular maintenance and has more costs associated with it. The electricity is used to power a mechanism that introduces the air into the effluent which the bacteria use to help in their digestion of the waste materials. Aerobic septic systems are often brought in to replace aging or failing anaerobic septic systems. An Aerobic septic system is also an option if you have limited space as they do not require a large piece of land to install like a traditional septic system does. Just so you know, sometimes an aerobic septic system is referred to as an aerator septic tank.

Aerobic Septic System Installation

When installing these units you have the option of installing them above ground or below ground. Whatever you decide, keep in mind that they require electrical connections and easy access for regular maintenance. You will also have to install a pretreatment set up, which the manufacturer will provide to you.

Aerobic Septic System Benefits/Costs

The cost of an aerobic system varies based on location, installation, size, design, and maintenance requirements. A good rule of thumb is that aerobic septic systems can cost two to three times as much as a traditional septic tank.
Savings created with an aerobic septic system are realized in a variety of ways. The aerobic units require less space and generally cause less groundwater pollution which is very important, especially if you live on well water. Savings can also be realized when the life of a drain fields is extended through the supplemental use of an aerobic system. If you’re drainage field ends up failing it can cost you tens of thousands of dollars to fix, so taking a load of the drainage field’s back can save you a lot.
One of the leading causes of septic system failure is lint from washing machines. For this reason all septic systems are required to have a washing machine (lint) filter. Having a lint filter is even more important with an aerobic septic system because they have tiny filters in them which are very easily clogged with lint. You will find that many manufacturers say that their systems do not require lint filters, but do not be fooled. They just do not want their system to look inferior compared to their competitor’s. If they are being honest, they will tell you that all septic systems require a lint filter. If they insist that you do not need a lint filter make sure that YOU insist upon one. At the end of the day it is your hard-earned money that you are investing in the septic system and you want it to last as long as possible.

Aerobic System Limitations

Aerobic septic systems require more upfront investment and more maintenance in the long term than a standard septic system. If you neglect your system or turn it off the treatment quality diminishes. If you pour harmful chemicals down the drain or the temperature in the aerobic tank is to low you will also be reducing the treatment quality. The aerobic bacteria will reduce the effluent’s ammonia contents but the nitrate content may be increased. So you may have to have a system that treats the effluent for nitrate.

Aerobic Septic System Codes and Regulations

Check with your local health department because aerobic systems are not allowed in all areas. Some areas do not want the drain field area to be reduced which will happen if you use an aerobic septic system; however, other jurisdictions do allow drain filed reduction or even its elimination as long as you have pre-treatment. You will find that in some areas aerobic systems are being used on a trial basis or only in the event of a failed standard septic system. NSF/ANSI 40 – 2000 Standard for Residential Water Treatment Systems documentation outlines the requirements and the approval process for aerobic septic systems. The approval for a aerobic units comes from local health departments or state authorities. Some requirements include alarms installed in the aerobic system to alert the homeowner of malfunctions and two years of manufacturer maintenance service.

Availability of Aerobic Systems

There are only a handful of aerobic treatment system manufacturers but the demand is increasing with the increasing demand for higher quality water treatment.

General information About Aerobic Systems

Generally an aerobic septic system is used when a standard septic system fails. There are times when a standard septic system with a drainage field cannot be installed because space requirements cannot be met. In that case an aerobic system is used in its place. Other situations in which aerobic treatment units are recommended include poor soil quality, bedrock or groundwater near the surface, large amounts of organic matter to be disposed of and the need for high quality water treatment in areas that are environmentally sensitive. Aerobic treatment systems provide higher-quality waste treatment because of the aerobic bacteria in conjunction with the air injection mechanisms.

Aerobic Septic System Designs

There are a variety of designs but they all have common features. These features include an aeration process, final disinfection/treatment, an area for suspended growth systems to operate, and pre-treatment to reduce the amount of clogging from solids. There are two main internal designs for aerobic systems, one is called “suspended growth” and the other is called “attached growth”. In the suspended growth design air is forced into the chamber which mixes with the liquids and the bacteria are suspended freely in the air/liquid solution. In the attached growth methods, the bacteria are attached to a surface that is alternately exposed to liquid and air.

Failing septic systems are a large concern because there is a heavy financial burden and environmental fallout associated with them. Throughout this country a large number of septic systems are failing and the financial costs as I said earlier can be in the tens of thousands of dollars. I am glad that you are doing your research into aerobic septic systems both for the benefits to the environment and the benefits for your bank account. There is one more thing you should know however, if you live in a house where the septic tank or septic tanks have failed you will not be able to sell the house until the septic systems are repaired and once again fully functional. In this case, it may be quicker, easier and cheaper to retrofit your failed system with an aerobic septic system if you are allowed to do so in your area. If you are not allowed, you may have to bite the bullet and pay up to have your system repaired and then sell your house.

SOLAR AND WIND POWER WATER PURIFICATION AND DESALINATION SYSTEM

2011-05-21T01:24:00.000-07:00

Swiss-based company TRUNZ WATER SYSTEMS has developed and manufactures and distributes a sustainable and cost-effective solution for water purification and desalination: a complete and ready-to-operate unit which is mobile and independent – thanks to renewable energy.

Solar and wind-powered water treatment and desalination systems

Trunz’s innovative and environmentally friendly technology produces clean drinking water from polluted water and saltwater using solar and / or wind energy. An ultrafiltration membrane or a reverse osmosis system (for sea or brackish water) removes all virus and bacteria (and salts) without requiring toxic chemical treatment.

Compact and mobile water purification systems

The Trunz Water Systems are compact, mobile and work without ongoing fuel costs. If necessary, the units can be mounted on a trailer or four-wheel-drive and easily relocated. The systems are complete with a borehole pump, solar racks as well as a wind generator, and are ready for installation. All of the Trunz Water Systems require minimal maintenance – they are equipped with an automatic back-flushing system to keep maintenance and service costs as low as possible. The capacity depends on the raw water quality and ranges from 7,000 to 24.000l a day. Additionally, the company provides engineering and manufacturing of tailor-made, containerised solutions for higher capacities.

Source

Desalination installation system design (Membrane technology)

2011-05-21T01:16:00.000-07:00

System design

The desalination installation is a complete system, with feed water input and separate discharge pipes for concentrate and permeate. The data of the input and output pipes should always be compared with water analysis, feed water pressure and salt retention.
The designer of a Reverse Osmosis system will aim at the lowest possible membrane pressure and installation costs and maximum recovery and salt retention.

The recovery of a desalination installation for brackish water is around 85%. It depends on the solubility of suspended solids that are present in the feed water. During seawater desalination a recovery of forty to fifty percent is desirable. The recovery of seawater desalination depends on the osmotic pressure of the feed water and the applied membrane types during the desalination process.

Continuous process

A membrane filtration system is usually designed to attend a continuous process. The choice for a continuous process can be made, because the process conditions, such as feed water flow and permeate flow, are continuous.

Schematic representation of a continuous process

The same goes for Reverse Osmosis systems. These are also designed to attend a continuous process with a continual permeate flow and a system recovery that is steady.
Variations in water temperature and fouling degree of the feed water are compensated by adjustments of the feed pressure.

Multi-stage system

Systems that consist of more than one stage are called multi-stage systems. These systems can reach higher system recoveries, without exceeding the single element recovery limits. To gain a recovery of up to 70%, two stages must be implemented in the feed water treatment system.

Schematic representation of a two-stage system

For higher recoveries, three stages must be used. These values are based on the assumption that standard pressure vessels with six elements are used. For shorter vessels the number of stages must be doubled.
When the system recovery is higher, more membrane elements have to be connected in series. A typical two-stage system uses a stage ratio of 2:1 for the desalination of seawater with high dissolved solids contents.

Plug-flow and concentrate recirculation

The plug-flow concept is the standard Reverse Osmosis system design for water desalination applications.
The feed water is passed through a plug-flow system only once. A fraction of the feed water passes a membrane to produce permeate. The rest of the feed water is not derived of salts and will become more and more concentrated.

When the number of membrane elements in a plug-flow system is too low to achieve a high enough system recovery, concentrate recirculation may be implicated. During recirculation part of the concentrate is directed back to the feed water side of the module. The recycled concentrate mixes with the feed water and will be treated once more.

Schematic representation of an installation with concentrate recirculation options

The number of elements in each pressure vessel

Reverse Osmosis systems are usually designed for a specific permeate flow. To achieve this flow, a number of membrane elements is required. The number of membrane elements that is placed within the installation depends upon the designed flux.
For the desalination of seawater the limiting factor is the maximum feed pressure; this may not exceeds 69 bars.

Based on the designed flux, the production per unit membrane can be determined:

Production per element = flux * element surface

Number of elements = permeate flow / production per element

Number of pressure vessels = number of elements / number of elements per vessel

By means of the permeate flow and the required recovery, the feed water flow is calculated:

Feed water flow = permeate flow / recovery

Feed water pressure

A certain feed pressure is required, depending on the system design. The flux, the energy loss in the system and the osmotic pressure determine the feed pressure that the system requires. The required feed pressure will increase when the membrane elements are becoming contaminated through the years. A feed pump that enables a higher flow than the flow that is theoretically required will than be implicated to keep the feed pressure continual. A feed pump that increases the feed pressure by 25% will be satisfactory in practise.
When the system is started up, the initial situation is recorded. All relevant parameters should be registered and noted in a log. Based on this data the performance of the installation can be examined and regulated after the system has been put into action.

Monitoring

During monitoring of the system, measurements will take place of the flow, pressure and conductivity of the water. To check the hydraulic affectivity of the system the feed pressure per stage and the permeate flow need to be measured. The feed pressure depends upon the temperature of the feed water. When feed water temperatures are low, more pressure is required to achieve the same recovery that would be reached when feed water temperatures are high. When water temperatures fluctuate, one needs to normalize the permeate flow, to enable comparison with the starting situation.

When the installations function correctly the conductivity of the permeate is low, because of the removal of univalent and bivalent ions. When a leak is situated in the membrane element, the conductivity will increase. That is why conductivity measurements are applied.
These measurements take place in the permeate collection drain. Measurements can be performed for each individual stack or for all present stacks.
A sufficient monitoring of the system will enable the user to know when the system needs cleaning.

Material protection

Within desalination installations, there is a course environment when it comes to corrosion of separate parts of the system. Because of this, the material needs to possess a certain resistance to corrosion. This goes for external parts, which are exposed to a salty atmosphere (spillage, leaks), as well as for internal parts. Corrosion of external system parts can usually be prevented by providing them with a surface layer (painting, galvanizing) and by periodic maintenance of the system and closing of leaks.
Despite the fact that materials are protected against potential corrosion, they also need to be able to be resistant to pressure, vibrations and changing temperatures.
To prevent corrosion and chemical reactions in the part of the system where pressures are low (<10 bar), such as in membrane elements and pressure vessels, non-metals such as PVC and fibreglass are often applied. For high-pressure parts (10-70 bar), such as pumps, drains and lids, one needs to use metals to provide them with the same kind of protection.
PVC and some metals cannot sufficiently resist corrosion. When they start corroding they can contaminate membranes. When corrosion protection is in order, we need to keep this in mind.
The main material that is used for high-pressure parts is stainless steel. The benefit of stainless steel is that it is resistant to corrosion and erosion corrosion. Stainless steel is rarely stricken by galvanic corrosion.

Pipes and parts of the installation should follow up demands of the company where the installation is located. Pipes and components of the installation are usually built using the following materials:

Candle filters and pressure vessel: polypropylene filter in PVC or stainless steel vessel
Pumps: stainless steel
Low-pressure pipes: PVC
High-pressure pipes: stainless steel
Cleansing system: PVC or other chemical-resistant synthetic material

Energy saving

In a desalination system the concentrate is released under high pressure, that is why it is important to win back energy from the concentrate flow. This can be done by application of a pressure exchanger. The concentrate flow from the membranes is directed through the pressure exchanger, where it directly transfers energy to part of the incoming feed water with maximum affectivity.
The feed water flow now has the same volume as the concentrate flow. It will be directed to a small booster pump that corrects the hydraulic losses of the flow.
The upgraded feed water flow will join the feed water flow from the high-pressure pump.
In an installation that uses a pressure exchanger, the high-pressure pump will give off 41% of the energy, the booster pump will give off 2% of the energy and the pressure exchanger will give off the remaining 57%. The pressure exchanger does not use any external energy, so the total energy savings will be 57%.

By practising pressure directly to incoming seawater in a membrane system, a reduction of 60% in size of the high-pressure pump can be achieved. This does not only save energy; it also saves purchase costs of high-pressure pumps.

ECONOMICS OF APPLIED TECHNOLOGIES FOR TREATMENT OF SEWAGE WASTEWATER

2011-05-14T06:29:00.000-07:00

Abstract

Relatively simple wastewater treatment technologies can be designed to provide low cost sanitation and environmental protection while providing additional benefits from the reuse of water. These technologies use natural aquatic and terrestrial systems. They are in use in a number of locations.

These systems may be classified into three principal types, as shown in Figure 1. Mechanical treatment systems, which use natural processes within a constructed environment, tend to be used when suitable lands are unavailable for the implementation of natural system technologies. Aquatic systems are represented by lagoons; facultative, aerated, and hydrograph controlled release (HCR) lagoons are variations of this technology. Further, the lagoon-based treatment systems can be supplemented by additional pre- or post-treatments using constructed wetlands, aquacultural production systems, and/or sand filtration. They are used to treat a variety of wastewaters and function under a wide range of weather conditions. Terrestrial systems make use of the nutrients contained in wastewaters; plant growth and soil adsorption convert biologically available nutrients into less-available forms of biomass, which is then harvested for a variety of uses, including methane gas production, alcohol production, or cattle feed supplements.

Figure 1: Summary of Wastewater Treatment Technologies

Mechanical	Oxidation ditch Extended aeration Sequencing batch reactor Trickling filter - SCP
Aquatic (Lagoons)	Facultative	Free water surface Subsurface flow
	Aerated	Aquacultrure	Water hyacinths Duckweed
	Aerated	Sand filters	Intermittent Recirculating
	HCR
Terrestrial	Slow rate Overland flow Rapid infiltration Subsurface infiltration

Technical Description

Mechanical Treatment Technologies

Mechanical systems utilize a combination of physical, biological, and chemical processes to achieve the treatment objectives. Using essentially natural processes within an artificial environment, mechanical treatment technologies use a series of tanks, along with pumps, blowers, screens, grinders, and other mechanical components, to treat wastewaters. Flow of wastewater in the system is controlled by various types of instrumentation. Sequencing batch reactors (SBR), oxidation ditches, and extended aeration systems are all variations of the activated-sludge process, which is a suspended-growth system. The trickling filter solids contact process (TF-SCP), in contrast, is an attached-growth system. These treatment systems are effective where land is at a premium.

Aquatic Treatment Technologies

Facultative lagoons are the most common form of aquatic treatment-lagoon technology currently in use. The water layer near the surface is aerobic while the bottom layer, which includes sludge deposits, is anaerobic. The intermediate layer is aerobic near the top and anaerobic near the bottom, and constitutes the facultative zone. Aerated lagoons are smaller and deeper than facultative lagoons. These systems evolved from stabilization ponds when aeration devices were added to counteract odors arising from septic conditions. The aeration devices can be mechanical or diffused air systems. The chief disadvantage of lagoons is high effluent solids content, which can exceed 100 mg/l. To counteract this, hydrograph controlled release (HCR) lagoons are a recent innovation. In this system, wastewater is discharged only during periods when the stream flow is adequate to prevent water quality degradation. When stream conditions prohibit discharge, wastewater is accumulated in a storage lagoon. Typical design parameters are summarized in Table 1.

Constructed wetlands, aquacultural operations, and sand filters are generally the most successful methods of polishing the treated wastewater effluent from the lagoons. These systems have also been used with more traditional, engineered primary treatment technologies such as Imhoff tanks, septic tanks, and primary clarifiers. Their main advantage is to provide additional treatment beyond secondary treatment where required. In recent years, constructed wetlands have been utilized in two designs: systems using surface water flows and systems using subsurface flows. Both systems utilize the roots of plants to provide substrate for the growth of attached bacteria which utilize the nutrients present in the effluents and for the transfer of oxygen. Bacteria do the bulk of the work in these systems, although there is some nitrogen uptake by the plants. The surface water system most closely approximates a natural wetland. Typically, these systems are long, narrow basins, with depths of less than 2 feet, that are planted with aquatic vegetation such as bulrush (Scirpus spp.) or cattails (Typha spp.). The shallow groundwater systems use a gravel or sand medium, approximately eighteen inches deep, which provides a rooting medium for the aquatic plants and through which the wastewater flows.

Table 1 Typical Design Features Aquatic Treatment Units

Technology	Treatment goal	Detention Time (days)	Depth (feet)	Organic Loading (lb/ac/day)
Oxidation pond	Secondary	10-40	3-4.5	36-110
Facultative pond	Secondary	25-180	4.5-7.5	20-60
Aerated pond	Secondary, polishing	7-20	6-18	45-180
Storage pond, HCR pond	Secondary, storage, polishing	100-200	9-15	20-60
Root zone Treatment, Hyacinth pond	Secondary	30-50	<4.5	<45

Aquaculture systems are distinguished by the type of plants grown in the wastewater holding basins. These plants are commonly water hyacinth (Eichhornia crassipes) or duckweed (Lemna spp.). These systems are basically shallow ponds covered with floating plants that detain wastewater at least one week. The main purpose of the plants in these systems is to provide a suitable habitat for bacteria which remove the vast majority of dissolved nutrients. The design features of such systems are summarized in Table 2.

Table 2 Typical Design Features for Constructed Wetlands

Design Factor	Surface water flow	Subsurface water flow
Minimum surface area	5-10 ac/mgd	2.3-46 ac/mgd
Maximum water depth	Relatively shallow	Water level below ground surface
Bed depth	Not applicable	1-2 ft
Minimum hydraulic residence time	7 days	7 days
Maximum hydraulic loading rate	0.2-1.0 gpd/sq ft	0.5-10 gpd/sq ft
Minimum pretreatment	Primary (secondary optional)	Primary
Range of organic loading as BOD	9-18 lb/ac/d	1.8-140 lb/ac/d

Sand filters have been used for wastewater treatment purposes for at least a century in Latin America and the Caribbean. Two types of sand filters are commonly used: intermittent and recirculating. They differ mainly in the method of application of the wastewater. Intermittent filters are flooded with wastewater and then allowed to drain completely before the next application of wastewater. In contrast, recirculating filters use a pump to recirculate the effluent to the filter in a ratio of 3 to 5 parts filter effluent to 1 part raw wastewater. Both types of filters use a sand layer, 2 to 3 feet thick, underlain by a collection system of perforated or open joint pipes enclosed within graded gravel. Water is treated biologically by the epiphytic flora associated with the sand and gravel particles, although some physical filtration of suspended solids by the sand grains and some chemical adsorption onto the surface of the sand grains play a role in the treatment process.

Terrestrial Treatment Technologies

Terrestrial treatment systems include slow-rate overland flow, slow-rate subsurface infiltration, and rapid infiltration methods. In addition to wastewater treatment and low maintenance costs, these systems may yield additional benefits by providing water for groundwater recharge, reforestation, agriculture, and/or livestock pasturage. They depend upon physical, chemical, and biological reactions on and within the soil. Slow-rate overland flow systems require vegetation, both to take up nutrients and other contaminants and to slow the passage of the effluent across the land surface to ensure maximum contact times between the effluents and the plants/soils. Slow-rate subsurface infiltration systems and rapid infiltration systems are "zero discharge" systems that rarely discharge effluents directly to streams or other surface waters. Each system has different constraints regarding soil permeability.

Although slow-rate overland flow systems are the most costly of the natural systems to implement, their advantage is their positive impact on sustainable development practices. In addition to treating wastewater, they provide an economic return from the reuse of water and nutrients to produce marketable crops or other agriculture products and/or water and fodder for livestock. The water may also be used to support reforestation projects in water-poor areas. In slow-rate systems, either primary or secondary wastewater is applied at a controlled rate, either by sprinklers or by flooding of furrows, to a vegetated land surface of moderate to low permeability. The wastewater is treated as it passes through the soil by filtration, adsorption, ion exchange, precipitation, microbial action, and plant uptake. Vegetation is a critical component of the process and serves to extract nutrients, reduce erosion, and maintain soil permeability.

Overland flow systems are a land application treatment method in which treated effluents are eventually discharged to surface water. The main benefits of these systems are their low maintenance and low technical manpower requirements. Wastewater is applied intermittently across the tops of terraces constructed on soils of very low permeability and allowed to sheet-flow across the vegetated surface to the runoff collection channel. Treatment, including nitrogen removal, is achieved primarily through sedimentation, filtration, and biochemical activity as the wastewater flows across the vegetated surface of the terraced slope. Loading rates and application cycles are designed to maintain active microorganism growth in the soil. The rate and length of application are controlled to minimize the occurrence of severe anaerobic conditions, and a rest period between applications is needed. The rest period should be long enough to prevent surface ponding, yet short enough to keep the microorganisms active. Site constraints relating to land application technologies are shown in Table 3.

Table 3 Site Constraints for Land Application Technologies

Feature	Slow Rate	Rapid Infiltration	Subsurface Infiltration	Overland Flow
Soil texture	Sandy loam to clay loam	Sand and sandy loam	Sand to clayey loam	Silty loam and clayey loam
Depth to groundwater	3 ft	3 ft	3 ft	Not critical
Vegetation	Required	Optional	Not applicable	Required
Climatic restrictions	Growing season	None	None	Growing season
Slope	<20%, cultivated land < 40%, uncultivated land	Not critical	Not applicable	2%-8% finished slopes

In rapid infiltration systems, most of the applied wastewater percolates through the soil, and the treated effluent drains naturally to surface waters or recharges the groundwater. Their cost and manpower requirements are low. Wastewater is applied to soils that are moderately or highly permeable by spreading in basins or by sprinkling. Vegetation is not necessary, but it does not cause a problem if present. The major treatment goal is to convert ammonia nitrogen in the water to nitrate nitrogen before discharging to the receiving water.

Subsurface infiltration systems are designed for municipalities of less than 2,500 people. They are usually designed for individual homes (septic tanks), but they can be designed for clusters of homes. Although they do require specific site conditions, they can be low-cost methods of wastewater disposal.

Extent of Use

These treatment technologies are widely used in Latin America and the Caribbean. Combinations of some of them with wastewater reuse technologies have been tested in several countries. Colombia has extensively tested aerobic and anaerobic mechanical treatment systems. Chile, Colombia, and Barbados have used activated sludge plants, while Brazil has utilized vertical reactor plants. Argentina, Bolivia, Colombia, Guatemala, Brazil, Chile, Curaçao, Mexico, Jamaica, and Saint Lucia have successfully experimented with different kinds of terrestrial and aquatic treatment systems for the treatment of wastewaters. Curaçao, Mexico, and Jamaica have used stabilization or facultative lagoons and oxidation ponds; their experience has been that aquatic treatment technologies require extensive land areas and relatively long retention times, on the order of 7 to 10 days, to adequately treat wastewater. An emerging technology, being tested in a number of different countries, is a hybrid aquatic-terrestrial treatment system that uses wastewaters for hydroponic cultivation. However, most of the applications of this hybrid technology to date have been limited to the experimental treatment of small volumes of wastewater.

Operation and Maintenance

Operation and maintenance requirements vary depending on the particular technology used. In mechanical activated-sludge plants, maintenance requirements consist of periodically activating the sludge pumps, inspecting the system to ensure that are no blockages or leakages in the system, and checking BOD and suspended solids concentrations in the plant effluent to ensure efficient operation.

In the case of aquatic treatment systems using anaerobic reactors and facultative lagoons for primary wastewater treatment, the following operational guidelines should be followed:

Periodically clean the sand removal system (usually every 5 days in dry weather, and every 2 to 3 days in wet weather).

Daily remove any oily material that accumulates in the anaerobic reactor.

Daily remove accumulated algae in the facultative lagoons.

Open the sludge valves to send the sludge to the drying beds.

Establish an exotic aquatic plant removal program (aquatic plant growth can hamper the treatment capacity of the lagoons).

Properly dispose of the materials removed, including dried sludge.

A preventive maintenance program should also be established to increase the efficiency of the treatment systems and prolong their lifespan.

When using terrestrial treatment systems or hybrid hydroponic cultivation systems for wastewater treatment, it is advisable to have two parallel systems, and to alternate applications of wastewater to these systems every 12 hours in order to facilitate aeration and to avoid damage to the system. Care is required to avoid hydraulic overload in these systems, as the irrigated plant communities could be damaged and the degree of treatment provided negated. Periodic removal of sediments accumulated in the soil is also required to improve the soil-plant interaction and to avoid soil compaction/subsidence.

Level of Involvement

Government involvement is essential in the implementation of most of the wastewater treatment technologies. The private sector, particularly the tourism industry, has successfully installed "packaged" or small-scale, self-contained sewage treatment plants at individual sites. In some cases, the installation of these plants has been combined with the reuse of the effluent for watering golf courses, lawns, and similar areas. The selection and construction of the appropriate wastewater treatment technology is generally initiated and financed, at least partially, by the government, with the subsequent operation and maintenance of the facility being a responsibility of the local community. Nevertheless, despite the large number of well-known and well-tested methods for wastewater treatment, there still exist a significant number of local communities in Latin America which discharge wastewater directly into lakes, rivers, estuaries, and oceans without treatment. As a result, surface water degradation, which also affects the availability of freshwater resources, is more widespread than is desirable within this region.

Suitability

Mechanical systems are more suitable for places where land availability is a concern, such as hotels and residential areas. Mechanical plants are the least land intensive of the wastewater treatment methods based on natural processes.

Lagoon and oxidation pond technologies are suitable where there is plenty of land available. Slow-rate systems require as much as 760 acres. Hybrid hydroponic cultivation techniques, using aquatic and terrestrial plants for the treatment for wastewater, also require relatively large amounts of land, and are best suited to regions where suitable aquatic plants can grow naturally.

Advantages

Table 5 summarizes the advantages of the various wastewater treatment technologies. In general, the advantages of using natural biological processes relate to their "low-tech/no-tech" nature, which means that these systems are relatively easy to construct and operate, and to their low cost, which makes them attractive to communities with limited budgets. However, their simplicity and low cost may be deceptive in that the systems require frequent inspections and constant maintenance to ensure smooth operation. Concerns include hydraulic overloading, excessive plant growth, and loss of exotic plants to natural watercourses. For this reason, and also because of the land requirements for biologically based technologies, many communities prefer mechanically-based technologies, which tend to require less land and permit better control of the operation. However, these systems generally have a high cost and require more skilled personnel to operate them.

Table 4 Comparative Performance of Sewage Treatment Systems

Process	Oxygen Supply	Reactor Volume	Retention Time	Removal Efficiency
Activated sludge	Pressurized air	10 m³	4-6 hr	90%-95% organic matter 90%-95% suspended solids
Biologic rotary discs	Air	1 m³	1-3 hr	90%-95% organic matter
Ascendant flow	Anaerobic	2 m³	24 hr	50%-60% organic matter 57% suspended solids
Anaerobic filtration	Anaerobic	2 m³	36 hr	40%-50% organic matter 52% suspended solids
Septic tank	Anaerobic	2 m³	36 hr	25% organic matter
Hydroponic cultivation	Aerobic/anaerobic	6 m³	12 hr	65%-75% organic matter

Disadvantages

Table 5 also summarizes the disadvantages of the various wastewater treatment technologies. These generally relate to the cost of construction and ease of operation. Mechanical systems can be costly to build and operate as they require specialized personnel. Nevertheless, they do offer a more controlled environment which produces a more consistent quality of effluent. Natural biological systems, on the other hand, are more land-intensive, require less-skilled operators, and can produce effluents of variable quality depending on time of year, type of plants, and volume of wastewater loading. Generally, the complexity and cost of wastewater treatment technologies increase with the quality of the effluent produced.

Further Development of the Technology

The cost-effectiveness of all wastewater treatment technologies needs to be improved. New designs of mechanical systems which address this concern are being introduced by the treatment plant manufacturing industry. The use of vertical reactors with an activated-sludge system, being tested in Brazil in order to acquire data for future improvement of this technology, is one example of the innovation going on in the industry. Similar product development is occurring in the use of aquatic and terrestrial plants and hybrid hydroponic systems, as a means of wastewater treatment; however, these technologies are still in an experimental phase and will require more testing and research prior to being accepted as standard treatment technologies. In addition, education to create an awareness of the need for wastewater treatment remains a critical need at all levels of government and private sector

Table 5 Advantages and Disadvantages of Conventional and Non-conventional Wastewater Treatment Technologies

Treatment Type	Advantages	Disadvantages
Aquatic Systems
Stabilization lagoons	Low capital cost Low operation and maintenance costs Low technical manpower requirement	Requires a large area of land May produce undesirable odors
Aerated lagoons	Requires relatively little land area Produces few undesirable odors	Requires mechanical devices to aerate the basins Produces effluents with a high suspended solids concentration
Terrestrial Systems
Septic tanks	Can be used by individual households Easy to operate and maintain Can be built in rural areas	Provides a low treatment efficiency Must be pumped occasionally Requires a landfill for periodic disposal of sludge and septage
Constructed wetlands	Removes up to 70% of solids and bacteria Minimal capital cost Low operation and maintenance requirements and costs	Remains largely experimental Requires periodic removal of excess plant material Best used in areas where suitable native plants are available
Mechanical Systems
Filtration systems	Minimal land requirements; can be used for household-scale treatment Relatively low cost Easy to operate	Requires mechanical devices
Vertical biological reactors	Highly efficient treatment method Requires little land area Applicable to small communities for local-scale treatment and to big cities for regional-scale treatment	High cost Complex technology Requires technically skilled manpower for operation and maintenance Needs spare-parts-availability Has a high energy requirement
Activated sludge	Highly efficient treatment method Requires little land area Applicable to small communities for local-scale treatment and to big cities for regional-scale treatment	High cost Requires sludge disposal area (sludge is usually land-spread) Requires technically skilled manpower for operation and maintenance

References

× Arjona, B. 1987. Evaluación de un Cultivo Hidropónico de Penissetus Clandestinum Hoschst (kikuyo) como Tratamiento Biológico para Aguas Residuales Domésticas. Bogotá, Universidad Nacional de Colombia. (Trabajo de grado)

× Barbosa, M., and G. Sarmiento. 1988. Estudios de Tratabilidad de las Aguas Residuales de Bogotá, Colector Salitre. Bogotá, Empresa de Acueducto y Alcantarillado de Bogotá, LAN-10. (Discos Biológicos Rotatorios)

× Cornejo, E., and R. Berolatti. 1991. Tratamiento de Aguas Servidas Mediante el Uso de Macrófitos Acuáticos. Puno, Perú, Convenio UNA-UBC-ACDI, IIAA.

× Fair, G. 1989. Purificación de Aguas y Tratamiento de Aguas Servidas. Vol II. México, D.F., Limusa. Guyot, J.P. 1988. Microbiología de la Digestión Anaeróbica. Medellín, Colombia, Universidad de Antioquía.

× Kraft, Harald. 1995. Draft Preliminary Report on Design, Construction and Management of a Root Zone Waste Water Treatment Plant at Hurricane Hole Hotel, Marigot Bay, Saint Lucia. Castries, CARICOM/GTZ Environmental Health Improvement Project.

× Huanacuni, V. 1991. Factores Ambientales del Tratamiento con Totora (Schoenoplectus Totora) en Aguas Servidas, Ciudad de Puno. Puno, Peru, UNA. (Tesis)

× Lettinga, G, et al. 1989. "High Rate Anaeróbio Waste Water Treatment Using the UASB Reactor Under a Wide Range of Temperature Conditions," Biotechnology and Genetic Engineering Review, 2.

× Martínez, I. 1989. Depuración de Aguas con Plantas Emergentes. Madrid, Ministério de Agricultura, Pesca y Alimentación.

× Reed, S.C., E. J. Middlebrooks, and R W. Crites. 1988. Natural Systems for Waste Management and Treatment. New York, McGraw-Hill.

× USEPA. 1980. Process Design Manual: Onsite Wastewater Treatment and Disposal Systems. Cincinnati, Ohio. (EPA Report No. EPA-625/1-80-012)

× 1980. Innovative and Alternative Technology Assessment Manual. Washington, D.C. (Report No. PA-430/9-78-009)

× 1980. Planning Wastewater Management Facilities for Small Communities. Cincinnati, Ohio. (Report No. EPA-600/8-80-030)

× 1981. Process Design Manual: Land Treatment of Municipal Wastewater. Cincinnati, Ohio. (Report No. EPA-625/1-81-013)

× 1983. Process Design Manual: Municipal Wastewater Stabilization Ponds. Cincinnati, Ohio. (Report No. EPA-625/1-83-015)

× 1988. Process Design Manual: Constructed Wetlands and Aquatic Plant Systems. Cincinnati, Ohio. (Report No. EPA-625/1-88-022)

× 1990. State Design Criteria for Wastewater Treatment Systems. Washington, D.C. (Report No. EPA-430/9-90-014)

× 1992. Process Design Manual: Wastewater Treatment/Disposal for Small Communities. Cincinnati, Ohio. (Report No. EPA-625/R-92/005)

GRAYWATER RECYCLING

2011-05-14T06:17:00.000-07:00

Introduction

Graywater is often seen as a benign material that poses a minimal threat to human health and the environment. For this reason, graywater has often been considered a good candidate for various types of reuse or disposal options rather than disposal in a conventional septic system. In this paper we look at several alternative designs which have been proposed locally for disposal of graywater. We consider the environmental impacts of graywater, and try to balance the cost of alternative disposal options against environmental gains they may provide. We also look at the public health considerations that must be incorporated into any graywater disposal design.

What is Graywater?

Graywater includes all household wastewater that doesn't come from toilets. This includes wastewater flows from baths/showers, clothes washing, dishwashers and, optionally, kitchen sinks. Toilet wastewater, and often garbage disposal waste, is called blackwater. Graywater comprises about 60% of typical household wastewater flow . Separation of graywater and blackwater is achieved through the use of separate plumbing. Wastewater separation is relatively easy to accomplish in new construction, but can range widely in cost and ease for retrofits of existing dwellings.

Bacterial Pathogens and Indicators

It is important to recognize that graywater is not always pathogen-free. Under some circumstances graywater may contain more pathogens than are normally found in combined (grey and black) wastewater. This is particularly true in households where a resident is sick or with infants where diapers are routinely laundered.

Numerous pathogenic organisms and microbial indicators have been found in graywater. These include coliform bacteria, fecal coliform including E. coli, (including enterotoxigenic strains), fecal streptococci including enterococci, Salmonella spp., Shigella spp., Vibrio cholerae, Campylobacter jejuni, Yersinia enterocolitica, Aeromonas hydrophila, Legionella pneumophila and other Legionellaceae, Mycobacterium tuberculosis and other mycobacteria, Staphylococcus aureus and other staphylococci, Pseudomonas aeruginosa, Klebsiella pneumoniae, Clostridium perfringens, enteric viruses including polioviruses, coxsackieviruses, echoviruses, hepatitis virus A, Norwalk virus, caliciviruses, astroviruses, reoviruses, rotaviruses and adenoviruses, and possibly Giardia cysts and Cryptosporidium oocysts. Many of these organisms are opportunistic pathogens which are more likely to affect older people, young children and individuals who are immuno-compromised (i.e. individuals who are HIV-infected, chronically ill, or are undergoing chemotherapy). Some of these organisms, such as enteric bacteria and viruses and Staphylococcus, are commonly found on the skin or in the oral cavity of humans and are shed routinely during bathing. According to Management of Small Waste Flows produced by the Small Scale Waste Management Project at the University of Wisconsin-Madison (USEPA publication EPA-600/2-78-173, 1978) bacterial indicators are higher in bathing wastewater than in laundry wastewater (Table 1) due to shedding. In comparison, mean concentrations of fecal coliform and fecal streptococci in septic tank effluents are only 10-100x greater than the high values cited for bathing wastewater. In recognition of the public health risks, conventional septic systems are designed to ensure that there is no surface breakout of septic tank effluent. Similarly, surface discharge of graywater, which may contain similar microorganisms at only 1-2

Table 1 Fecal coliform and nitrogen in wastewater

Source	Fecal Coliform per 100 ml	Total nitrogen mg/l
Toilet	1,000,000	200
Bathing	1,000	20
Kitchen Sink		75
Laundry	100	20
Garbage Disposal		80

orders of magnitude lower concentration than septic tank effluent, should be controlled.

Graywater should not be applied to the soil surface in areas where humans or pets have easy access unless the graywater is first disinfected.

Other Pollutants

In general graywater is perceived as being relatively clean and low in nutrients or other pollutants. While it is true that graywater is relatively low in nitrogen (most of which is found in toilet wastes), graywater can contain significant amounts of BOD, phosphorus and total suspended solids (Table 2). Biochemical oxygen demand (BOD) in graywater may equal or exceed the BOD content of blackwater. This is primarily because of food waste and grease from kitchen drains. Also due to kitchen sink flows, total suspended solids (TSS) may equal those found in toilet wastes and will far exceed toilet flows when a garbage disposal is used. The phosphorus content of graywater may equal that found in toilet wastes due to the continued use

Table 2. Wastewater Pollutant Contributions in grams per person per day.

Source	BOD (5 day)	TSS	Total Nit	Total Phos.
Toilet	6.9-24	13-37	4.1-17	0.6-1.6
Garbage Disposal	11-31	16-44	0.2-0.9	0.1
Greywater	25-39	11-23	1.1-2.0	2.2-3.4

of phosphate-containing detergents. Massachusetts prohibited the sale of phosphate-containing detergents in July 1994, with the exception of detergents used for automatic dishwashers. In a typical residential home these detergents can contribute an amount of phosphorus equal to that found in toilet wastes.

General Considerations for Design of Graywater Systems

Graywater must be treated before discharge. The conventional treatment method, a septic tank large enough to provide at least a two-day retention time, allows grease to cool, solidify and float to the top. This is particularly important when kitchen wastes are part of the graywater flow. Also, longer retention times allow fine solid materials suspended in the wastewater to sink to the bottom of the tank.

The 1995 Title 5 allows the use of a filter in place of a septic tank when only graywater is being disposed of. Several proprietary filters are available. For example, Clivus New England Inc. markets a three-stage aerobic intermittent sand filter. Graywater first flows through a mesh filter which catches large solids and then through a layer of coarse-grained sand. It next passes through a screen filter and into a proprietary media where biological oxidation occurs. Biomat is expected to form at each filter stage to attenuate bacteria and trap solids. There is limited information on the effectiveness, longevity and maintenance requirements of this and many residential graywater filters. In designing or evaluating any graywater filter it is important to recognize that the grease and kitchen solids found in graywater may clog filters. The BOD and nutrients present will promote bacterial growth that may also clog filters and necessitate frequent cleaning.

Increased longevity of the leaching system and reduced maintenance of the grey water system may be achieved if the kitchen sink is not plumbed into the graywater system. Garbage disposals should be strongly discouraged as they can stress even a conventional septic system and will provide an overwhelmingly high solids load to a system designed to handle only graywater. If a garbage disposal is installed it should be plumbed to the blackwater system.

What Innovative Designs are Available for Disposal of Graywater?

Reduced Size Conventional Leaching Facility

The simplest way to dispose of graywater is a conventional soil absorption facility. Under the 1995

Title 5, if graywater alone is discharged the leaching facility may be sized for 60% of the building's design flow. A septic tank is not required for disposal of graywater only. A filter system specifically approved by DEP may be used in place of the septic tank as long as no garbage disposal waste or liquid waste from a composting toilet enters the graywater disposal system. A conventional leaching facility will generally be the lowest cost alternative for disposal of graywater, averaging $2000-3000 to install. How thoroughly does a conventional leaching field treat graywater? Properly sited leaching facilities with adequate separation to groundwater will act efficiently to remove bacteria and many viruses through simple filtration and adsorption. Filtration will also provide almost complete removal of total suspended solids. Substantial reductions in BOD should also be achieved as the effluent passes through the biomat that surrounds the leach field. The amount of phosphorus removal will largely depend on the soil type in which the leaching system is installed: sands generally have less capacity to attenuate phosphorus while clay or silt soils may attenuate significant amounts of phosphorus. Conventional leaching facilities also provide recharge to the groundwater that other innovative designs may not.

Shallow Drip Soil Absorption Systems

A relatively new design for disposal of graywater is the shallow drip soil absorption system. This system has been used in agriculture for many years to irrigate crops using a network of shallow underground pipes fed by a pump. It delivers water at a controlled rate for uptake in the root zone minimizing percolation of water. When used to dispose of graywater the.drip system also has the advantage of using the treatment capability of the surrounding soil to further treat the graywater. Nutrient and organic constituents in the effluent are removed by vegetation or are degraded by microorganisms as effluent moves through the soil. Thus, the quality of effluent treatment is directly linked to the soil and site characteristics such as soil permeability, drainage, slope, and depth to limiting conditions such as bedrock or groundwater.

How it works: graywater first enters the pre-treatment unit (a septic tank, sand filter, etc.) and flows by gravity to a pump chamber or dosing tank. The collected effluent is periodically pumped under pressure to the subsurface drip field. The drip field consists of parallel rows of polyethylene tubing with drip emitter holes (pinhole size) at about two-foot intervals. The emitters distribute the effluent at a slow and controlled rate to a large surface area of soil. This allows the system to operate over long periods without saturating the surrounding soil. It also allows the system to be installed at a shallow depth, usually 6 to 18 inches below the surface. An additional benefit of the design is the use of treated effluent to water shrubbery and gardens.

The drip emitter design is often modified in northern climates where the ground freezes solidly in winter. In addition to the drip tubing these designs incorporate a deeper leaching trench of pressure-dosed perforated PVC pipe laid in a gravel bed 24-36 inches below the ground surface. Piping from the dosing tank leads to a series of valves so that graywater flow can beshunted to either the drip irrigation bed or the deeper leaching trench depending on season of the year.

A potential problem with drip emitter systems is biological and chemical clogging of filters, drip lines, and emitters. Chemical clogging can be caused by a high solids content in the effluent. Residual solids may deposit in the emitter holes if water evaporates out of it between doses, and the resulting buildup of solids around the drip hole may eventually slow the system's rate of flow. Similarly, salts deposited by evaporation of effluent may also form deposits around the emitter holes and slow flow. Clogging can generally be avoided if the system is flushed routinely (2-4 times per year). This can be accomplished by designing the system so that a garden hose can be connected and high pressure water forced through the system. Alternatively, use of a sand filter to pretreat the effluent before it flows to the drip tubing may eliminate the need for flushing. The sand filter greatly reduces the total suspended solids and BOD content of the effluent that should minimize biological clogging of the system.

A typical household drip disposal system costs about $4000-6000 to install. While this is more expensive than a conventional disposal system it can compare favorably with other alternative disposal options, especially where there are limiting site conditions such as slowly permeable soils or high groundwater. An additional cost of operating the system is the cost of hiring a certified operator who will oversee and periodically flush the system.

Where may the installation of shallow drip disposal systems be most appropriate? The goal of a drip system is to make maximum use of soil treatment capabilities. Drip disposal systems may work well in sandy soils where the effluent is applied in the finer textured topsoil layer where it receives better filtration than it would otherwise receive in the underlying sand. Also, effluent filters through the soil more slowly than in a conventional system, providing better attenuation of pollutants in soils with a fast percolation rate. Because of the slow rate at which effluent is applied, drip systems may also be suitable for marginally usable clay or silt soils where conventional systems will not work.

Other Shallow Disposal Systems

Another type of shallow disposal system utilizes 1 inch perforated PVC pipe laid at 6-18 inches below the surface. The system design is similar to the drip system, including a pretreatment unit and dosing chamber which pressure doses the disposal field. The irrigation bed can be laid at a depth of 6 inches directly in the topsoil, or at a depth of 18 inches in the underlying soil (with or without gravel surrounding the pipe). Many systems use pipe installed at both 6 and 18 inches for summer and winter use, respectively.

As with the drip system, treatment of the effluent is accomplished by biological processes in the surrounding soil and by the fact that effluent is applied at a slow rate. Thus, installation of this type of system is appropriate in situations similar to those discussed for drip systems. The system may also be better able to handle solids than a drip system because the holes in the PVC pipe are larger than those in the drip tubing and are thus less likely to clog.

Closed Evapotranspiration Systems

Yet another strategy for disposal of graywater is to drain the filtered graywater to a specially constructed sealed garden unit. In this type of system graywater is distributed either by pressure or gravity through a series of pipes laid in a gravel bed within a lined excavation. A layer of sand is laid over the gravel and planted with selected plants. The sand acts as a wick to draw the water to the surface for evaporation while the plants take up the graywater by their roots, utilize the nutrients for growth, and transpire the water as vapor. Designs of this type are constructed as no-discharge units where theoretically all water is disposed of by evapotranspiration. The units may be located either indoors in a greenhouse-type design or outdoors in constructed beds.

Several design considerations are key to the success of these units. Firstly, success of the system depends on the evaporation rate of the bed exceeding the rate of effluent loading plus precipitation. This may necessitate a very low effluent loading rate, especially for beds constructed outdoors. Secondly, the sand or gravel used to construct the bed must be large grained enough to ensure that the bed drains thoroughly and remains aerobic. If more water is received than can be evaporated, or if the bed drains poorly, the soil pore space will remain saturated and will tend to go anaerobic causing the plants to die. In addition, if the bed drains poorly there is the chance that graywater will come to the soil surface that is not desirable (and also not legal under Massachusetts health regulations). Evaporative capacity of the bed will vary with both climate (solar radiation, temperature, humidity, wind speed, precipitation) and with the type of plants selected for use. If the bed is constructed outdoors it will likely function at reduced or minimal capacity in winter when precipitation exceeds evaporation. In this case, an alternative provision such as leaching trenches or a tight tank should be made for graywater disposal.

A potential long-term problem with evapotranspiration systems is the buildup of salts left in the soil by the effluent as it evaporates. With time salt concentration may increase to the point where it is harmful to vegetation. Plants in the beds may also have to be fertilized occasionally since graywater usually contains little nitrogen.

Cost of installation can vary widely largely based on whether the unit is constructed indoors or out. The costs of household units consisting of a lined bed constructed outdoors can vary widely. One recently installed in Wellfleet cost approximately $ 5,000 . If a tight tank must be installed to handle excess flow this will present an additional cost to install and pump. Because evapotranspiration systems produce zero discharge (and are usually coupled with a composting toilet which should also create zero discharge), these systems are most appropriate where soil conditions are limiting (high groundwater, impermeable soils) or where inadequate setbacks to wells or watercourses exist

Figure 2. Schemata of Graywater Evapotranspiration Bed Installed in Wellfleet

It should be recognized that evapotranspiration units are somewhat experimental and often require some trial and error with dosing rate or plant types used before they function properly. Because there is no standard design for evapotranspiration units all designs should be viewed with scrutiny before approval. These designs must also be approved on a case-by-case basis by DEP before installation. A detailed design module entitled Onsite Wastewater Disposal Evapotranspiration and Evapotranspiration Absorption Systems produced by National Small Flows Clearinghouse is available by request to our department for Boards of Health or engineers who may be considering designs for systems of this type.

Scenarios Where Innovative Graywater Systems May Be Proposed

What are the most likely scenarios that Boards of Health will encounter where innovative graywater disposal systems are proposed? Where may innovative graywater designs provide a good solution to wastewater disposal?

Where an existing septic system is failing hydraulically, it may be possible to install composting toilets and allow graywater to flow to the existing cesspool or septic system. In repair situations (remedial use), DEP will allow graywater to be disposed of in an existing cesspool under the following conditions: a composting toilet is used for human waste; there is no discharge of garbage grinder waste or liquid waste from the composter; the cesspool is pumped and cleaned; the cesspool is not located in groundwater; the cesspool meets the design criteria of 310 CMR 15.253 (design criteria for pits, galleries, or chambers); and the effluent loading requirements of Title 5 are met. Because the total volume of water is reduced and because graywater contributes a lower solids and BOD load than combined wastewater the existing septic system may be able to hydraulically function if it receives only graywater. A number of systems of this type have been approved by DEP elsewhere in Massachusetts and seem to be functioning well. This appears to be a cost effective way for homeowners to deal with some hydraulically failing systems.

Where an existing septic system has been deemed to have failed because of insufficient setbacks to wetlands or watercourses, use of the existing septic system or an innovative shallow trench design for graywater only may also be appropriate. Setbacks to watercourses are determined primarily to ensure that pathogens are removed by soil filtration before wastewater intercepts a watercourse. Removal of the toilet waste to a composting toilet (or tight tank) will remove the majority of pathogens from the wastewater. It will also remove most of the nitrogen and approximately half of the BOD and phosphorus thereby reducing nutrient loading to the water.body. Use of a shallow trench to further treat graywater may provide additional reduction in pathogens, BOD, and phosphorus loading.

A more difficult scenario is presented by septic systems that are deemed failed because of inadequate separation to groundwater. Obviously, the best solution in this scenario is to create a mounded leaching system so that adequate separation can be maintained. Where small lot size prevents this, compromise must be made. Title 5 allows a reduction to a two foot separation distance to groundwater for combined (grey and black) wastewater for local upgrade approvals when no other option for siting the leaching system exists (310 CMR 15.415). In this extreme case, it seems much preferable to remove the toilet wastes (to composter or tight tank) and allow only graywater to be disposed of with reduced separation to groundwater. Use of a shallow trench system, preferably located in topsoil, to further treat graywater may provide additional reduction in pathogens, and secondarily in BOD and phosphorus loading. Or, use of a closed evapotranspiration bed and composter will provide a zero-discharge system.

A similar scenario is presented by existing septic systems that have inadequate setbacks to drinking wells. The 1995 Title 5 allows a reduction to a 50 foot setback to a well for a combined wastewater disposal system. In the extreme case where a 50 foot setback cannot be met, or where hydrogeologic conditions warrant further protection, a closed graywater evapotranspiration bed and toilet composter zero-discharge system may be the best solution.

A last (and more pleasant) scenario is presented by the home owner who wishes to voluntarily install a composting toilet and graywater disposal system in the belief that these will benefit the environment. The beliefs that motivate this choice range from a desire to conserve water in general to a desire to protect our embayments and ponds from nutrient loading and to a desire to protect groundwater from various drinking water pollutants. How well will use of a composting toilet and graywater system achieve these goals? Installation of a composting toilet can reduce household water use by up to 40% (although this can also be achieved by using ultra low flush toilets). Removal of toilet waste from household wastewater will also significantly reduce pathogen and nitrogen loading to the disposal system (however, see discussion in the section on Composting Toilets as to if and when these systems truly qualify as nitrogen removal systems). Total phosphorus discharge may also be halved. This can result in significant improvements in groundwater quality beneath the disposal system.

Some Concluding Thoughts

Careful consideration needs to be given to the issue of whether the cost of construction of an innovative graywater disposal system equals the benefit received. Conventional leaching systems that meet the requirements of Title 5 probably renovate graywater fairly completely with the possible exception of removing phosphorus. Shallow trench systems, which generally cost at least twice as much to install, may provide additional treatment in summer months when effluent is applied in the topsoil but may not provide any treatment beyond that of a conventional system in winter months when effluent is applied in the deeper soil layers. Closed evapotranspiration systems must be very large to function effectively in our climate, are costly to build, and probably are cost effective only in the most extreme circumstances when other disposal alternatives are limited. Innovative graywater systems have been proposed, and are often marketed, as a solution to protect our groundwater. Proponents make the argument that innovative graywater disposal will protect groundwater from pollution by pathogens and nutrients. They also propose that use of innovative graywater systems will benefit groundwater in other ways. Firstly, if composting toilets are used less household water will be needed, resulting in less groundwater withdrawal. Secondly, if the groundwater withdrawn for household use is later disposed of as relatively clean graywater, it is argued that the groundwater has been recharged with clean,.rather than polluted, water. Is the amount of water recharged from a graywater disposal system significant and does it provide a net benefit to groundwater?

Most of the graywater disposal systems discussed in this document are designed to rely largely on evaporation and evapotranspiration to dispose of graywater. This implies that these systems produce little to no recharge of graywater to the groundwater. Even if all the graywater discharged is recharged to groundwater, it still makes up only a tiny percentage of the total annual recharge to groundwater. Cape Cod receives about 40 inches of rain per year, about 18 inches of which is recharged to the groundwater (the rest being lost to evapotranspiration by natural plant communities during summer months). This results in a net recharge to the groundwater of about 488,800 gallons of water per acre per year (1.5 ft. of rain x 43,560 sf/acre= 65,340 ft³/acre X 7.481 gal/ft³= 488,808 gal/acre). A graywater disposal system, which produces a net contribution to groundwater of 100 gal/acre/day, results in 3650 gal/acre/year recharge to the groundwater. This constitutes less than 1% of the total recharge to the groundwater over that land surface.

Recently, proponents of composting toilets and innovative graywater systems have urged DEP and the state legislature to allow the use of graywater disposal systems (in repair situations) with minimal setbacks: a 1 foot vertical separation to groundwater and/or bedrock, a 5 foot horizontal separation to surface waters, wetlands and other environmentally sensitive areas, and a 50 foot horizontal separation to surface drinking waters. Given the information we know about graywater, and the present lack of information about the presence or absence of viruses in graywater, we believe that these setbacks are not sufficiently restrictive to protect public health.

Filtration and Coagulation

2011-05-11T14:26:00.000-07:00

hello dears
This is a good lectures on filtration and coagulation process in water treatment plants

In situ chemical oxidation

2011-05-11T08:51:00.000-07:00

In situ chemical oxidation
From Wikipedia, the free encyclopedia
(Redirected from In situ oxidation)

In situ chemical oxidation (ISCO), a form of advanced oxidation processes and advanced oxidation technology, is an environmental remediation technique used for soil and/or groundwater remediation to reduce the concentrations of targeted environmental contaminants to acceptable levels. ISCO is accomplished by injecting or otherwise introducing strong chemical oxidizers directly into the contaminated medium (soil or groundwater) to destroy chemical contaminants in place. It can be used to remediate a variety of organic compounds, including some that are resistant to natural degradation.
Chemical oxidation is one half of a redox reaction, which results in the loss of electrons. One of the reactants in the reaction becomes oxidized, or loses electrons, while the other reactant becomes reduced, or gains electrons. In ISCO, oxidizing compounds, compounds that give electrons away to other compounds in a reaction, are used to change to change the contaminants into harmless compounds.The in situ in ISCO is just Latin for "in place", signifying that ISCO is a chemical oxidation reaction that occurs at the site of the contamination.

The remediation of certain organic substances such as chlorinated solvents(trichloroethene and tetrachloroethene), and gasoline-related compounds (benzene, toluene, ethylbenzene, MTBE, and xylenes) by ISCO is possible. Some other contaminants can be made less toxic through chemical oxidation.
A wide range of ground water contaminants react either moderately or highly with the ISCO method, and ISCO can also be used in a variety of different situations (ex. unsaturated vs saturated ground, above ground or underground, etc), so it is a popular method to use.

Contents
1 History
2 Agents of Oxidization
2.1 Permanganate
2.2 Fenton's Reagent
2.3 Persulfate
2.4 Ozone
3 Implementation
3.1 Injection Probes
3.2 Hydraulic Fracturing
3.3 Soil Mixing
3.4 Horizontal and Vertical Wells
3.5 Treatment Walls
4 Case Studies
4.1 Naval Air Station North Island
4.2 Space Launch Complex 37
4.3 Nebraska Ordnance Plant
5 Performance Application

History

Fenton's reagent (hydrogen peroxide catalyzed with iron) and potassium permanganate are the oxidants that have been used the longest, and are now used the most widely. The systems of using hydrogen peroxide were based on the work of H.J.H. Fenton, who used iron salts to catalyze the compound. Hydrogen peroxide was first used in 1985 to treat a formaldehyde spill at Monsanto's Indian Orchard Plant in Springfield, Massachusetts. At this site, a 10% solution of hydrogen peroxide was injected into a formaldehyde plume. Fenton's reagent was initially used to treat hydrocarbon sites where benzene, toluene, and ethylbenzene were present.

As the industry shifted its focus to the remediation of chlorinated solvents, hydrogen peroxide was found to be effective in both the hydrocarbon industry and the chlorinated solvent industry. Scientists also found that permanganate could be used on chlorinated solvents. Permanganate based ISCO started to be used in the late 1990's. At this time, ISCO had also become and established remedial technology.
The development of sodium persulfate for ISCO began in the late 1990's because of the limitations in using peroxide or permanganate as oxidants. Peroxide has such a short life that it can not be transported properly. Permanganate only treats chlorinated solvents with double bonds and is easily used up by organic material in soil. Persulfate is more stable, treats a wider range of contaminants, and is not used up by soil organics as easily.

Agents of Oxidization
Common oxidants used in this process are permanganate (both sodium permanganate and potassium permanganate), Fenton's Reagent, persulfate, and ozone. Other oxidants can be used, but these four are the most commonly used.

Permanganate
Permanganate is used in groundwater remediation in the form of potassium permanganate (KMnO4) and sodium permanganate (NaMnO4). Both compounds have the same oxidizing capabilities and limitations and react similarly to contaminants. The biggest difference between the two chemicals is that potassium permanganate is less soluble than sodium permanganate.
Potassium permanganate is a crystalline solid that is typically dissolved in water before application to the contaminated site.Unfortunately, the solubility of potassium permanganate is dependent on temperature. Because the temperature in the aquifer is usually less than the temperature in the area that the solution is mixed, the potassium permanganate becomes a solid material again. This solid material then does not react with the contaminants. Over time, the permanganate will become soluble again, but the process takes a long time.This compound has been shown to oxidize many different contaminants but is notable for oxidizing chlorinated solvents such as perchloroethylene (PCE), trichloroethylene (TCE), and vinyl chloride (VC).

However, potassium permanganate is unable to efficiently oxidize diesel, gasoline, or BTEX.
Sodium permanganate is more expensive than potassium permanganate, but because sodium permanganate is more soluble than potassium permanganate, it can be applied to the site of contamination at a much higher concentration. This shortens the time required for the contaminant to be oxidized. Sodium permanganate is also useful in that it can be used in places where the potassium ion cannot be used.Another advantage that sodium permanganate has over potassium permanganate is that sodium permanganate, due to its high solubility, can be transported above ground as a liquid, decreasing the risk of exposure to granules or skin contact with the substance.
The primary redox reactions for permanganate are given by the equations:

The advantage of using permanganate in ISCO is that it reacts comparatively slowly in the subsurface which allows the compound to move further into the contaminated space and oxidize more contaminants. Permanganate can also help with the clean up of materials that are not very permeable. In addition, because both sodium permanganate and potassium permanganate solutions have a density greater than water's density, permanganate can travel through the contaminated area through density-driven diffusion.
The use of permanganate creates the byproduct MnO2, which is naturally present in the soil and is therefore a safe byproduct. Unfortunately, several studies have shown that this byproduct seems to cement sand particles together forming rock-like material that has very low permeability. As the rock-like materials build up, it blocks the permanganate from getting to the rest of the contaminant and lowers the efficiency of the permanganate. This can be prevented by extracting the MnO2 from the contaminated area.

Fenton's Reagent
Fenton's reagent is basically a mixture of ferrous iron salts as a catalyst and hydrogen peroxide. A similar sort of reaction can be made by mixing hydrogen peroxide with [ferric] iron (Iron III). At a low pH, it forms hydroxyl radicals(·OH) that oxidize contaminants such as chlorinated solvents, fuel oils, and BTEX. Unfortunately, the contaminated groundwater that needs to be treated has a pH level that is at or near neutral. Due to this, there are controversies on whether ISCO using Fenton's reagent is really a Fenton reaction. Instead, scientists call these reactions Fenton-like.
The Fenton chemistry is complex and has many steps including the following [7]:
Fe2+ + H2O2 → Fe3+ + OH· + OH−
Fe3+ + H2O2 → Fe2+ + OOH· + H+
HO· + H2O2 → Fe(III) + HO2· + H+
HO· + Fe(II) → Fe(III) + OH−
Fe(III) + HO2· → Fe(II) + O2H+
Fe(II) + HO2· + H+ → Fe(III) + H2O2
HO2· + HO2· → H2O2 + O2
These reactions do not occur step by step but simultaneously.
When applied to In Situ Chemical Oxidation, the collective reaction results in the degradation of contaminants in the presence of Fe2+ as a catalyst. The overall end result of the process can be described by the following reaction:
H2O2 + contaminant → H2O + CO2 + O2

Advantages of this method include that the hydroxyl radicals are very strong oxidants and react very rapidly with contaminants and impurities in the ground water. Moreover, the chemicals needed for this process are inexpensive and abundant.
This method, however, is very exothermic. Over the course of the reaction, the water starts beating up and, in some cases, can boil water out of the soil. The chemicals used in the process are detrimental to microbes and rapidly degrade the soil, so Fenton's reagent must be used with extreme caution. The hydroxyl radicals also react with many other substances other than the targeted contaminant, so it is not as effective in soils containing carbonate, bicarbonate, and organic matter.

Persulfate
Persulfate is a newer oxidant used in ISCO technology. The persulfate compound that is used in groundwater remediation is in the form of peroxodisulfate or peroxydisulfate (S2O2−8) but is generally called a persulfate ion by scientists in the field of environmental engineering. More specifically, sodium persulfate is used because it has it has the highest water solubility and its reaction with contaminants leaves least harmful side products. Although sodium persulfate by itself can degrade many environmental contaminants, the sulfate radical SO−4 is usually derived from the persulfate because sulfate radicals can degrade a wider range of contaminants at a faster pace(about 1,000-100,000 times) than the persulfate ion. Various agents, such as heat, ultraviolet light, high pH, hydrogen peroxide, and transition metals, are used to activate persulfate ions and generate sulfate radicals.

The sulfate radical is an electrophile, a compound that is attracted to electrons and that reacts by accepting an electron pair in order to bond to a substance called a nucleophile.Therefore the performance of sulfate radicals is enhanced in an area where there are many electron donating organic compounds. The sulfate radical reacts with the organic compounds to form an organic radical cation. Examples of electron donating groups present in organic compounds are the amino (-NH2), hydroxyl (-OH), and alkoxy (-OR) groups. Conversely, the sulfate radical does not react as much in compounds that contain electron attracting groups like nitro (-NO2) and carbonyl (C=O) and also in the presence of substances containing chlorine atoms. Also, as the number of ether bonds increases, the reaction rates decrease.
When applied in the field, persulfate must first be activated (it must be turned into the sulfate radial) to be effective in the decontamination. The catalyst that is most commonly used is ferrous iron (Iron II). When ferrous iron and persulfate ions are mixed together, they produce ferric iron (iron III) and two types of sulfate radicals, one with a charge of -1 and the other with a charge of -2. New research has shown that Zero Valent Iron (ZVI) can also be used with persulfate with success.The persulfate and the iron are not mixed beforehand, but are injected into the area of contamination together. The persulfate and iron react underground to produce the sulfate radicals. The rate of contaminant destruction increases as the temperature of the surroundings increases.

The advantage of using persulfate is that persulfate is much more stable than either hydrogen peroxide or ozone above the surface and it does not react quickly by nature. This means fewer transportation limitations, it can be injected into the site of contamination at high concentrations, and can be transported through porous media by density driven diffusion. The disadvantage is that this is an emerging field of technology and there are only a few reports of testing it in the field and more research needs to be done with it.

Ozone
While oxygen is a very strong oxidant, it's elemental form O2 is not very soluble in water. This poses a problem in ground water remediation, because the chemical must be able to mix with water to remove the contaminant. Fortunately, ozone (O3) is about 12 times more soluble than O2 and, although it is still comparably insoluble, it is a strong oxidant.
The unique part of ozone oxidation is its in-situ application. Because, unlike other oxidants used in ISCO, it is a gas, it needs to be injected into the contamination site from the bottom rather than the top. Tubes are built into the ground to transport the ozone to its starting place; the bubbles then rise to the surface. Whatever volatile substances are left over are sucked up by a vacuum pump. Because the bubbles travel more vertically than horizontally, close placement of ozone injection wells is needed for uniform distribution.

The biggest advantage in using ozone in ISCO is that ozone does not leave any residual chemical like persulfate leaves SO2−4 or permanganate leaves MnO2. The processes involved with ozonation (treating water with ozone) only leave behind O2. Ozone can also react with many of the important environmental contaminants. In addition, because ozone is a gas, adding ozone to the bottom of the contaminant pool forces the ozone to rise up through the contaminants and react. Because of this property, ozone can also be delivered more quickly. Also, in theory, H2O2 co-injected with ozone will result in -OH ions, which are very strong oxidants.
However, ozone has many properties that pose problems. Ozone reacts with a variety of contaminants, but the problem is that it also reacts quickly with many other substances such as minerals, organic matter, etc. that are not the targeted substances. Again, it is not very soluble and stays in gas form in the water, which makes ozone prone to nonuniform distribution and rising up to the top of contamination site by the shortest routes rather than traveling through the entire material. In addition, ozone must be generated, and that requires a huge amount of energy.

Implementation
Application of ozone during in-situ chemical oxidation
The primary delivery mechanism for ISCO is through perforated, hollow metal rods hammered into the ground by "direct-push" drilling methods or by injecting the oxidant into wells installed using hollow stem auger, rotary drilling methods. One advantage of injection wells is that they can be used for multiple applications of the oxidant material, while direct push injection techniques are generally quicker and less expensive. Injection wells for ozone are typically constructed of a 1-2" stainless-steel screen set in sand pack, grouted to the surface using a combination of cement and bentoine clay. Often, a field pilot study must be performed to determine injection parameters and well spacing.
Oxidants such as Permanganate and Fenton's Reagent are delivered as water-based solutions. These substances are injected into the aquifer and then allowed to propagate by gravity and water current. As contaminants are encountered, the substances oxidize them and purify the water. Ozone is delivered (sparged) as a gas in either a dry air or oxygen carrier gas. Specialized equipment is required for in-situ oxidation via ozone gas injection. The ozone has to be pumped into the groundwater from the bottom of the aquifer because the ozone gas is less dense than the water. As the ozone travels through the aquifer against gravity, it reacts with contaminants along the way. However, there are some specific methods of oxidant delivery including injection probes, hydraulic fracturing, soil mixing, vertical wells, horizontal wells, and treatment walls.

Injection Probes
Injection probes are used in areas where there is very low permeability. A small diameter probe (2 to 4 cm in diameter) is rotated or pushed into the ground while reagents are inserted into it at low pressure. The reagents travel down the core of the probe and exit out though small perforations along the sides of the probe which are located at certain intervals. The reagents travel away from the core by going into existing cracks and pores and create a "halo of reactivity" (from pg. 182 or Principles and Practices of In Situ Chemical Oxidation Using Permanganate). In order to optimize the amount of contaminant that is oxidized, the probes are set into the ground relatively close together, about .6-1.2 meters apart.

Hydraulic Fracturing
Hydraulic fracturing is the process of artificially creating fractures in a site that has low permeability and then filling the fractures with oxidants. First a hole is drilled into the ground, and then a forceful jet of water is used to create fractures. Course sand, which allows just enough permeability for oxidants to get though, is used to fill the fractures and prevent them from closing up, and after that, the oxidant is injected into the fracture.

Soil Mixing
Soil mixing can be used to deliver solid or liquid forms of oxidants to contaminated soil. For near surface contamination, standard construction equipment can be used. In order to apply this method in-situ and in deep soil, the oxidant must be pumped through a kelly bar (a piece of earth drilling equipment) to the place where the soil needs to be oxidized. The soil then has to be mixed by using mixing blades attached to the kelly bar.

Horizontal and Vertical Wells
Horizontal and vertical well networks are basically the use of long pipes that lead in and out of the contaminated aquifer or plume used to inject oxidants and extract the treated ground water. Vertical wells consist of one injection well and a number of extraction wells surrounding it. Horizontal well networks work similarly, but the pipe is slightly L-shaped at the bottom and injects oxidants and extracts treated groundwater horizontally. Horizontal wells are used especially when oxidants need to be delivered to thin layers of saturation.

Treatment Walls
Treatment walls are used to deliver oxidants to the end of a contaminant plume and can be used to prevent the migration of an oxidant. The walls usually consist of continuous trenches that are connected to a piping network into which oxidants can be injected into. Another version of this delivery system is the use of a disconnected series of vertical wells to inject the oxidant into the ground water. The factors that affect treatment wall application and performance are similar to the factors that effect the performance of permeable reactive barriers.

Case Studies
The ISCO technology has been tested many times in the field. The following are a few examples of studies that have been conducted to observe the effectiveness of ISCO.
[edit]Naval Air Station North Island
In January of 2007, the groundwater around the Naval Air Station North Island in San Diego County, California. This test treated a total of 60,000 gallons of groundwater and used about 22,646 pounds of sodium persulfate to do it. No catalysts were added to the persulfate, but there was a significant amount of contaminant reduction. The production of radical was concluded to be due to the elevated temperature of the groundwater (20°C-24°C). At the end of 19 days after the last injection of sodium persulfate, there was an overall TCE concentration reduction of greater than 90%.
[edit]Space Launch Complex 37
Space Launch Complex 37 supported the Saturn spacecraft launches from 1961-1971. Activities in the Complex included parts cleaning and engine flushing, which left two chlorinated volatile organic compound (CVOCs) source areas. The United Launch Allliance also used the area for launching the Delta IV launch vehicles prior to any remediation activities on the site. Maximum concentrations of CVOCs in the site were 9500 micro grams/Liter of cis 1,2-DCE and 7900 micro grams/Liter of vinyl chloride. Both sites were cleaned up with the use of ozone. An ozone injection grid was used that consisted of 116 stainless steel wells. After 16 months of ozone treatment, there was a contaminant mass reduction of 44% in one site and 70% in the other site.

Nebraska Ordnance Plant
The Nebraska Ordnance Plant is located near Mead, Nebraska was a military facility in World War II that produced bombs, rockets, and shells. In the process of creating these products, high explosives like 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) were used; to reduce the plant's workers' chemical exposure to these materials, RDX and TNT residues that collected on the floor were washed away with water routinely. The water went outside and into unlined ditches. The soil in the plant consequently became contaminated with RDX and TNT. Use of trichloroethene (TCE) to degrease pipelines further contaminated the area. The contaminants over the course of fifty years has also entered the groundwater in that area.
In order to stop the spread of the contaminated groundwater, an elaborate system of 11 extraction wells has been placed to contain the plumes. This method treats the water with granular activated carbon. This field was chosen as a testing site to see how effectively permanganate could remove explosive contaminants. On the field, two injection wells were placed so that a curtain of permanganate existed between them through which the contaminant plume would flow through. The results of the oxidation was a temporary decrease of the contaminant in the wells by 70-80%, but permanganate was not evenly distributed through the curtain. However, the test showed that permanganate was an effective tool to use to remove explosive contaminants from groundwater.

Performance Application
The effectiveness of the oxidation is contingent on the site lithology, the residence time of the oxidant, the amount of oxidant used, the presence of oxidizing materials other than the targeted contaminant, the degree of effective contact between the oxidant and the contaminant(s), and the kinetics of the oxidation reaction between the oxidant and contaminant.
The soil and groundwater are tested both before and after oxidant application to verify the effectiveness of the process. Monitoring of gases given off during oxidation can also help determine if contaminants are being destroyed. Elevated levels of CO2 is an indicator of oxidation.

SIROFLOC - unique method of water treatment

2011-05-11T04:00:00.000-07:00

The SIROFLOC process is a unique method of water treatment developed by CSIRO. It removes colour and turbidity from surface and groundwaters by the use of recyclable magnetic powders (magnetite). Clarification involves the magnetisation of the particulate matter, which aggregates and settles rapidly, so the clarifier is much smaller than in the conventional plant. There is no filter and the clarifying agent can be re-used. The advantages of this Australian invention over a full-scale conventional plant are lesser capital cost, low head loss across the plant, and much less sludge for disposal.

The work on the SIROFLOC process led by Don Weiss and Tony Priestley was awarded a CSIRO Medal for Research Achievement in 1989 and Tony Priestley was awarded a Clunies Ross Medal by the Australian Academy of Technological Sciences and Engineering (ATSE) in 1993.

Contents

The invention of SIROFLOC
Commercialisation of SIROFLOC
Application to sewage treatment
Global impact
Source

1-The invention of SIROFLOC
In the late 1970s, CSIRO researchers at the Division of Chemical Technology invented a new process for the treatment of water for potable supply. The processes of coagulation and flocculation induced by the addition of metal salts had formed the standard approach to potable water treatment for most of the 20th century. There are even records which suggest that the Romans used the coagulating power of 'aluminous earths' to clarify their water supplies.

The CSIRO invention, called SIROFLOC, was based on the chemical and magnetic properties of very fine particles of magnetite, a magnetic form of iron oxide. The researchers found that cleaning the magnetite particles with a dilute solution of caustic soda changed the electric charge characteristics on the magnetite surface thus allowing it to interact with negatively charged colloidal particles in the raw water. During the late 1970s, this phenomenon was developed into a very rapid process for water clarification, where the magnetic properties of the fine magnetite particles allowed for their rapid removal and recycling.

2-Commercialisation of SIROFLOC
The process was successfully commercialised in the early 1980s with the construction and operation of a full scale demonstration plant at Mirrabooka in Perth. Further development and commercialisation in partnership with Davy McKee Pacific Pty Ltd and the Water Corporation of Western Australia resulted in the first commercial SIROFLOC plant being installed in Bell Bay, Tasmania in 1983 which was still in operation 25 years after its commissioning. Since that time, SIROFLOC plants have been installed and successfully operated in England, Ireland, New Zealand and Taiwan.

3-Application to sewage treatment
The process has also been successfully applied to the treatment of raw sewage, where its ability to rapidly remove suspended solids and colloidal particles makes it an attractive treatment option in situations of limited land availability. At the opening of the first large-scale SIROFLOC sewage treatment plant at Malabar in 1993, Sydney sewage was cleaned up in fifteen minutes. The plant, a joint venture by the Sydney Water Board, CSIRO, and Davy John Brown Pty Ltd, removed 85% of suspended solids and 90% of oils and greases. Conventional plants would take over 10 hours to achieve the same results. At the official opening of the Malabar facility Dr John Stocker, CSIRO's Chief Executive, said:

The SIROFLOC process for sewage treatment has really come of age. The high level of purification in such a short time was beyond everyone's expectations. The SIROFLOC process not only protects the environment, but also supports Australian industry and has great export potential.

Without the investment and foresight of the Sydney Water Board, the engineering expertise of Davy John Brown, and CSIRO waste water research, SIROFLOC would not have progressed to this stage in such a relatively short time.

The plant is extremely compact, making it suitable for cities where urban space is a problem. SIROFLOC plants will suit cities in Japan, Korea, Taiwan and Europe, as well as Australia. SIROFLOC sewage plants are a cost effective way to upgrade existing plants, and as stand-by plants to process peak sewage loads. The Sydney Water Board and CSIRO invested $4.5 million each to research and develop the plant, with Davy John Brown providing the engineering and construction expertise. Davy John Brown is worldwide licensee for the SIROFLOC process.

4-Global impact
The SIROFLOC technology was recognised throughout the water industry as a major innovation in water treatment technology. It is in use in Britain, parts of the Middle East and South-East Asia and has spawned the development of a number of similar technologies in Europe.

5-Source
Priestley AJ, 2010, Personal communication.

Desalination

2011-05-09T10:18:00.000-07:00

Water is desalinated in order to convert salt water to fresh water so it is suitable for human consumption or irrigation. Sometimes the process produces table salt as a by-product. Desalination is used on many seagoing ships and submarines. Most of the modern interest in desalination is focused on developing cost-effective ways of providing fresh water for human use in regions where the availability of fresh water is, or is becoming, limited.
Large-scale desalination typically uses extremely large amounts of energy as well as specialized, expensive infrastructure, making it very costly compared to the use of fresh water from rivers or groundwater.

However, along with recycled water this is one of the only non-rainfall dependent water sources particularly relevant to countries like Australia which traditionally have relied on rainfall in dams to provide their drinking water supplies.
The world's largest desalination plant is the Jebel Ali Desalination Plant in the United Arab Emirates. It is a dual-purpose facility that uses multi-stage flash distillation and is capable of producing 300 million cubic metres of water per year. By comparison the largest desalination plant in the United States is located in Tampa Bay, Florida and operated by Tampa Bay Water, which began desalinating 34.7 million cubic meters of water per year in December 2007.The Tampa Bay plant runs at around 12% the output of the Jebel Ali Desalination Plants. A January 17, 2008, article in the Wall Street Journal states, "World-wide, 13,080 desalination plants produce more than 12 billion gallons of water a day, according to the International Desalination Association.

Methods
The traditional process used in these operations is vacuum distillation—essentially the boiling of water at less than atmospheric pressure and thus a much lower temperature than normal. This is because the boiling of a liquid occurs when the vapor pressure equals the ambient pressure and vapor pressure increases with temperature. Thus, because of the reduced temperature, energy is saved. A leading distillation method is multi-stage flash distillation accounting for 85% of production worldwide in 2004.

Reverse osmosis desalination plant in Barcelona, Spain
The principal competing processes use membranes to desalinate, principally applying reverse osmosis technology.[citation needed] Membrane processes use semi-permeable membranes and pressure to separate salts from water. Reverse osmosis plant membrane systems typically use less energy than thermal distillation, which has led to a reduction in overall desalination costs over the past decade. Desalination remains energy intensive, however, and future costs will continue to depend on the price of both energy and desalination technology.

Considerations and criticism

Cogeneration
Cogeneration is the process of using excess heat from power production to accomplish another task. For desalination, cogeneration is the production of potable water from seawater or brackish groundwater in an integrated, or "dual-purpose", facility in which a power plant is used as the source of energy for the desalination process. The facility’s energy production may be dedicated entirely to the production of potable water (a stand-alone facility), or excess energy may be produced and incorporated into the energy grid (a true cogeneration facility). There are various forms of cogeneration, and theoretically any form of energy production could be used. However, the majority of current and planned cogeneration desalination plants use either fossil fuels or nuclear power as their source of energy. Most plants are located in the Middle East or North Africa, due to their petroleum resources and subsidies. The advantage of dual-purpose facilities is that they can be more efficient in energy consumption, thus making desalination a more viable option for drinking water in areas of scarce water resources.

Shevchenko BN350, a nuclear-heated desalination unit
In a December 26, 2007, opinion column in the The Atlanta Journal-Constitution, Nolan Hertel, a professor of nuclear and radiological engineering at Georgia Tech, wrote, "... nuclear reactors can be used ... to produce large amounts of potable water. The process is already in use in a number of places around the world, from India to Japan and Russia. Eight nuclear reactors coupled to desalination plants are operating in Japan alone ... nuclear desalination plants could be a source of large amounts of potable water transported by pipelines hundreds of miles inland..."
Additionally, the current trend in dual-purpose facilities is hybrid configurations, in which the permeate from an RO desalination component is mixed with distillate from thermal desalination. Basically, two or more desalination processes are combined along with power production. Such facilities have already been implemented in Saudi Arabia at Jeddah and Yanbu.
A typical aircraft carrier in the U.S. military uses nuclear power to desalinate 400,000 US gallons (1,500,000 l; 330,000 imp gal) of water per day.

Economics
A number of factors determine the capital and operating costs for desalination: capacity and type of facility, location, feed water, labor, energy, financing, and concentrate disposal. Desalination stills now control pressure, temperature and brine concentrations to optimize the water extraction efficiency. Nuclear-powered desalination might be economical on a large scale.
While noting that costs are falling, and generally positive about the technology for affluent areas that are proximate to oceans, one study argues that "Desalinated water may be a solution for some water-stress regions, but not for places that are poor, deep in the interior of a continent, or at high elevation. Unfortunately, that includes some of the places with biggest water problems." and "Indeed, one needs to lift the water by 2,000 metres (6,600 ft), or transport it over more than 1,600 kilometres (990 mi) to get transport costs equal to the desalination costs. Thus, it may be more economical to transport fresh water from somewhere else than to desalinate it. In places far from the sea, like New Delhi, or in high places, like Mexico City, high transport costs would add to the high desalination costs. Desalinated water is also expensive in places that are both somewhat far from the sea and somewhat high, such as Riyadh and Harare. In many places, the dominant cost is desalination, not transport; the process would therefore be relatively less expensive in places like Beijing, Bangkok, Zaragoza, Phoenix, and, of course, coastal cities like Tripoli.After being desalinated at Jubail, Saudi Arabia, water is pumped 200 miles (320 km) inland through a pipeline to the capital city of Riyadh.For cities on the coast, desalination is being increasingly viewed as an untapped and unlimited water source.

Desalination makes sense only after less expensive options are exhausted, including recycling water and fixing broken infrastructure.[citation needed] Water is reused in Las Vegas NV, Fountain Valley CA, Fairfax VA, El Paso TX and Scottsdale AZ. Compared to desalinated sea water, recycling requires 50% less energy due to the significantly lower salt content and produces new water at 30% less cost to the consumer, without the damage to marine life and ecosystems common to desalination plants.

Israel is now desalinating water at a cost of US$0.53 per cubic meter.Singapore is desalinating water for US$0.49 per cubic meter. Many large coastal cities in developed countries are considering the feasibility of seawater desalination, due to its cost effectiveness compared with other water supply options, which can include mandatory installation of rainwater tanks or stormwater harvesting infrastructure. Studies[citation needed] have shown that the desalination option is more cost-effective than large-scale recycled water for drinking, and more cost-effective in Sydney than the vastly expensive option of mandatory installation of rainwater tanks or stormwater harvesting infrastructure. The city of Perth has been successfully operating a reverse osmosis seawater desalination plant since 2006, and the Western Australian government have announced that a second plant will be built to serve the city's needs. A desalination plant is now operating in Australia's largest city of Sydney,and the Wonthaggi desalination plant under construction in Wonthaggi, Victoria.

The Perth desalination plant is powered partially by renewable energy from the Emu Downs Wind Farm. A wind farm at Bungendore in NSW has been purpose-built to generate enough renewable energy to offset the energy use of the Sydney plant,mitigating concerns about harmful greenhouse gas emissions, a common argument used against seawater desalination due to the energy requirements of the technology. The purchase or production of renewable energy to power desalination plants naturally adds to the capital and/or operating costs of desalination. However, recent experience in Perth and Sydney indicates that the additional cost is acceptable to communities, as a city may then augment its water supply without doing environmental harm to the atmosphere. The Queensland state government also purchased renewable energy certificates on behalf of its Gold Coast plant which will see the plant offset its carbon emissions for the initial 18 to 20 months of operations, bringing its environmental footprint down, in line with the other major plants that will be operating around the same time, in Perth and Sydney.

In December 2007, the South Australian government announced that it would build a seawater desalination plant for the city of Adelaide, Australia, located at Port Stanvac. The desalination plant is to be funded by raising water rates to achieve full cost recovery.An online, unscientific poll showed that nearly 60% of votes cast were in favor of raising water rates to pay for desalination.

A January 17, 2008, article in the Wall Street Journal states, "In November, Connecticut-based Poseidon Resources Corp. won a key regulatory approval to build the US$300 million water-desalination plant in Carlsbad, north of San Diego. The facility would produce 50,000,000 US gallons (190,000,000 l; 42,000,000 imp gal) of drinking water per day, enough to supply about 100,000 homes ... Improved technology has cut the cost of desalination in half in the past decade, making it more competitive ... Poseidon plans to sell the water for about US $950 per acre-foot [1,200 cubic metres (42,000 cu ft)]. That compares with an average US$700 an acre-foot [1200 m³] that local agencies now pay for water." $1,000 per acre-foot works out to $3.06 for 1,000 gallons, or $.81 for 1 cubic meter, which is the unit of water measurement that residential water users are accustomed to being billed in.
While this regulatory hurdle was met, Poseidon Resources is not able to break ground until the final approval of a mitigation project for the damage done to marine life through the intake pipe, as is required by California law. Poseidon Resources has made progress in Carlsbad, CA, despite its unsuccessful attempt to complete construction of Tampa Bay Desal, a desalination plant in Tampa Bay, FL, in 2001. The Board of Directors of Tampa Bay Water were forced to buy Tampa Bay Desal from Poseidon Resources in 2001 to prevent a third failure of the project. Tampa Bay Water faced five years of engineering problems and operation at 20% capacity due to marine life and growth captured and stuck to reverse osmosis filters prior to fully utilizing this facility in 2007.
According to a May 9, 2008, article in Forbes, a San Leandro, California, company called Energy Recovery Inc. has been desalinating water for US $0.46 per cubic meter.
According to a June 5, 2008, article in the Globe and Mail, a Jordanian-born chemical engineering doctoral student at the University of Ottawa, named Mohammed Rasool Qtaisha, has invented a new desalination technology that is alleged to be between 600% and 700% more water output per square meter of membrane than current technology. According to the article, General Electric is looking into similar technology, and the U.S. National Science Foundation announced a grant to the University of Michigan to study it as well. Because the patents were still being worked out, the article was very vague about the details of this alleged technology.
While desalinating 1,000 US gallons (3,800 l; 830 imp gal) of water can cost as much as $3, the same amount of bottled water costs $7,945.
Environmental
Intake

One of the main environmental considerations of ocean water desalination plants is the impact of the open ocean water intakes, especially when co-located with power plants. Many proposed ocean desalination plants' initial plans relied on these intakes despite perpetuating ongoing impacts on marine life[citation needed]. In the United States, due to a recent court ruling under the Clean Water Act, these intakes are no longer viable without reducing mortality, by 90%, of the life in the ocean; the plankton, fish eggs and fish larvae. There are alternatives, including beach wells that eliminate this concern, but require more energy and higher costs while limiting output.Other environmental concerns include air pollution and greenhouse gas emissions from the power plants.
Outflow

To limit the environmental impact of returning the brine to the ocean, it can be diluted with another stream of water entering the ocean, such as the outfall of a waste water treatment plant or power plant. While seawater power plant cooling water outfalls are not freshwater like waste water treatment plant outfalls, the salinity of the brine will still be reduced. If the power plant is medium- to large-sized and the desalination plant is not enormous, the flow of the power plant's cooling water is likely to be at least several times larger than that of the desalination plant. Another method to reduce the increase in salinity is to spread the brine via a diffuser to mix in a mixing zone so that there is only a slight increase in salinity. For example, once the pipeline containing the brine reaches the sea floor, it can split off into many branches, each one releasing the brine gradually along its length through small holes. This method can be used in combination with the joining of the brine with power plant or waste water plant outfalls.
There are methods of desalination, particularly in combination with open pond evaporation (solar desalination), that do not discharge brine back into the ocean at all.
The concentrated seawater has the potential to harm ecosystems, especially marine environments in regions with low turbidity and high evaporation that already have elevated salinity. Examples of such locations are the Persian Gulf, the Red Sea and, in particular, coral lagoons of atolls and other tropical islands around the world.

The UAE, Qatar, Bahrain, Saudi Arabia, Kuwait and Iran have 120 desalination plants between them. These plants flush nearly 24 tons of chlorine, 65 tons of algae-harming antiscalants used to descale pipes, and around 300 kg of copper into the Persian Gulf every day.
Because the brine is denser than the surrounding sea water due to the higher solute concentration, discharge into water bodies means that the ecosystems on the bed of the water body are most at risk because the brine sinks and remains there long enough to damage the ecosystems. Careful re-introduction can minimize this problem[citation needed]. For example, for the desalination plant and ocean outlet structures to be built in Sydney from late 2007, the water authority states that the ocean outlets will be placed in locations at the seabed that will maximize the dispersal of the concentrated seawater, such that it will be indistinguishable from normal seawater between 50 and 75 metres (160 and 246 ft) from the outlet points. Sydney is fortunate to have typical oceanographic conditions off the coast that allow for such rapid dilution of the concentrated byproduct, thereby minimizing harm to the environment.

In Perth, Australia, in 2007, the Kwinana Desalination Plant was opened. The water is sucked in from the ocean at only 0.1 metres per second (0.33 ft/s), which is slow enough to let fish escape. The plant provides nearly 140,000 cubic metres (4,900,000 cu ft) of clean water per day.This is the same at Queensland's Gold Coast Desalination Plant and Sydney's Desalination Plant.

Reference
http://en.wikipedia.org/wiki/Desalination

lectures on water treatment plant

2011-05-09T06:46:00.000-07:00

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