Water Chemistry

Relationship between BOD, COD, TOC and ThOD

2009-11-12T17:48:00.001+05:30

For a completely biodegradable wastewater such as glucose, approximately ten percent of the original organics remain as non-biodegradable cellular residues after biological oxidation. Hence, the cellular residues are not measured by the BOD test. Therefore:

BODu = 0.9ThOD ---1

where BODu = ultimate BOD

ThOD = theoretical oxygen demand For domestic sewage and some biodegradable industrial wastes, the relationship between BOD5 and BODu is:

BOD5 = 0.77BODu ---2

where BOD5 = 5 day BOD

BODu = ultimate BOD

For most wastewaters:

ThOD = COD ---3

where ThOD = theoretical oxygen demand

COD = chemical oxygen demand since the COD test oxidizes all organics except for those which are totally resistant to dichromate oxidation.

Stoichiometrically, the COD/TOC ratio should be approximately the molecular ratio of oxygen to carbon:

COD/TOC =32/12= 2.66 ---4

The ratio will actually range from zero, when organic material is resistant to dichromate oxidation, to as much as 6.0 when inorganic reducing agents are present.

For raw domestic sewage and some biodegradable industrial wastes, the following ratio of BOD5/TOC occurs:

BOD5/TOC =32/12(0.90)(0.77) = 1.85 ---5

where BOD5 = 5 day BOD

TOC = Total Organic Carbon

0.90 = BOD5/BODu as per ---1
0.77 = BODu/ThOD as per ---2
As a wastewater is oxidized through a wastewater treatment plant, the BOD5/TOC ratio will drop. A treatment plant effluent may have a BOD5 /TOC ratio of as low as 0.5 since the effluent wastewater is so much less biodegradable. (It has already been largely degraded).

The BOD5 to COD ratio for domestic waste and certain biodegradable industrial wastes can be computed as follows:

BOD5 = 0.7 COD ---6

where BOD5 = 5 day BOD

COD = chemical oxygen demand

0.7 = 1.85 /2.66

               1.85 = BOD5/TOC as per --5
               2.66 = COD/TOC as per   --4
                 This ratio can also vary widely depending on the state of biodegradation of the wastewater. The author has found this ratio as low as 0.1 after several days of oxidation. If the BOD of a biodegradable wastewater equals zero, the wastewater will be completely biodegraded. There is some controversy about whether this ever occurs. Many authors will say that the Non-biodegradable Residue (NBDR) is as high as 0.10 as explained in the first paragraph of this section. The author has found that in activated sludge systems with hydraulic detention times in the range of 14 days, there is no accumulation of volatile suspended solids, which indicates that all organics are ultimately degraded under certain anoxic conditions.

Abbreviations of Water Analysis Terms

2009-09-27T15:15:00.001+05:30

a
AOBr
AOCl
AOI
AOX
b
B0
B5
BOD
BOD5
BODS
BODSEED
c
CBOD
COD
CL
CMWD
D0
D5
DBP
DO
DOC
DOX
ECD
ECNI
EOX
EPA
f

f ’
FAAS
FIA
FI–CL
GC
HAA
HAA5
HAA9
HBOD
HTC
HX
IC
ICP–AES
LOD
MS
MW
NDIR
NOM
NDOC
NPOC
NPOX
NVOC
OMWD
P
POC
POX
R
RSD
TAME
TC
THM
ThOD
TIC
TOC
TOBr
TOCl
TOI
TOX
US
USD
UV
VOC
Vsample

Volume of titrating solution employed with the blank
Adsorbable organic bromine
Adsorbable organic chlorine
Adsorbable organic iodine
Adsorbable organic halide
Volume of titrating solution employed with the sample
Dissolved oxygen in the dilution water before incubation
Dissolved oxygen in the dilution water after 5 days of incubation at 20 Deg C
Biochemical oxygen demand
Biochemical oxygen demand after an incubation period of 5 days
BOD supplied by sensors
Formulated uniform dehydrated microbial consortium for BOD estimation
Normality of the titrating solution
Carbonaceous BOD
Chemical oxygen demand
Chemiluminescence
Closed microwave-assisted digestion
Dissolved oxygen in the diluted sample after preparation
Dissolved oxygen in the diluted sample after 5 days of incubation at 20 Deg C
Disinfection by-products
Dissolved oxygen
Dissolved organic carbon
Dissolved organic halide
Electron capture detection
Electron capture negative ionization
Extractable organic halide
Environmental Protection Agency
ratio of the % seed in the diluted water to the % seed in the dilution water

titrating solution correction factor
Flame atomic absorption spectrometry
Flow injection analysis
Flow-injection chemiluminescence
Gas chromatography
Haloacetic acids
Five species of HAAs currently regulated
Nine species of HAAs
Headspace biochemical oxygen demand
High-temperature combustion
Hydrogen halide
Inorganic carbon
Inductively coupled plasma–atomic emission spectrometry
Iimit of detection
Mass spectrometry
Microwave radiation
Nondispersive infrared spectrometry
Natural organic matter
Nondissolved organic carbon
Nonpurgeable organic carbon
Nonpurgeable organic halide
Nonvolatile organic carbon
Open microwave-assisted digestion
Decimal volumetric fraction of sample used
Purgeable organic carbon
Purgeable organic halide
Regression coefficient
Relative standard deviation
Tert-amyl methyl ether
Total carbon
Trihalomethanes
Theoretical chemical oxygen demand
Total inorganic carbon
Total organic carbon
Total organic bromine
Total organic chlorine
Total organic iodine
Total organic halide
Ultrasound radiation
Ultrasound-assisted digestion
Ultraviolet
Volatile organic carbon
Volume of the water sample analyzed

What is Extended Aeration?

2009-08-04T14:36:00.001+05:30

In Extended Aeration, This process takes raw sewage directly into an aerated mix tank for 8 h or more to provide bacteria with optimum conditions to consume the BOD present in the wastewater. The effluent from this mix tank goes to a sedimentation tank where the flocculated colonies of organisms are settled to produce a clear overflow.

Extended Aeration Process Scheme.

A portion of the settled microbial floc is returned to the head works and a portion sent to sludge disposal. The clear effluent is then directed to final treatment such as disinfection, perhaps passing through a final polishing filter. This method of
treatment is particularly suited to plants that have a low concentration of settleable solids in the raw sewage. It minimizes the number of unit operations involved in smaller plants.

What is Solubility | Molarity

2009-07-13T17:14:00.001+05:30

Solids, liquids, and gases may dissolve in water to form solutions. The amount of solute present may vary below certain limits, so-called solubility. The strength of a solution can be expressed in two ways:

(1) weight (lb) of active solute per 100 pounds (i.e. %) and

(2) weight of active solute per unit volume (gallons or liters) of water.

Either expression can be computed to the other if the density or specific gravity is known. If the solution is dilute (less than 1%), the specific gravity can be assumed to be 1.0; i.e. 1 L of solution is equal to 1 kg and 1 gal of solution equals 8.34 lb.
In water chemistry, molarity is defined as the number of gram-molecular weights or moles of substance present in a liter of the solution. If solutions have equal molarity, it means that they have an equal number of molecules of dissolved substance per unit volume. The weight of substance in the solution can be determined as follows:
The molarity (M) of a solution can be expressed as:

M (mol/L) = moles of solute (mole) / 1.0 L of solution

For uniform purpose,

the Normality (N) is used for preparation of laboratory solutions. The
normality can be written as:
N (eq/L or meq/L) = equivalent of solute (eq or meq) / 1.0 L of solution

Integrity Test Procedure of Ultrafiltration Module

2009-07-06T17:37:00.002+05:30

Integrity Test is very essential to evaluate whether the module/element’s present state is good or it is going to end of life. Integrity Test is really means of fiber repair procedure.

The test is very useful for OUT to IN Flow style element Like DOW and Hyflux

Requirement:

You will need the following to complete the fiber repair

procedure:

• Concentrate tube plug

• Air supply apparatus

• Oil-free compressed air [recommended pressure: 3.0 bars (44 psi)]

• Loctite 406 glue

• Repair pins

• Personal protection equipment (gloves, safety glasses, etc.)

• Knife or diagonal cutters

Figure 1. Integrity test Feed Valve (OFF)Con. Valve (OFF)Air Inlet Valve (ON) PI Transparent TubePermeate Valve (ON)Observe whether air bubbles continuously appear

Procedure:

The bubble test using transparent tubes has been selected to illustrate how it is done.

1. Take the module out of the filtration mode.

2. Drain the module from the feed side.

3. Close feed and concentrate valve and keep the permeate valve open.

4. Pressurize the drained side of the module with oil-free compressed air from the air inlet valve, and slowly raise the air pressure to 1.5 bars (21 psi). Some displaced water will flow out the permeate side.

5. If large continuous air bubbles appear in the transparent tube then the module has broken fibers. Smaller and infrequent bubbles are the result of air diffusion through the pores of the ultrafiltration membrane. If leaks are confirmed, move to STEP 2.

Step-2

1. Drain the module from the feed side.

2. Remove the top end cap. Keep the bottom end cap on.

3. Isolate the module to perform repair by closing valves or sealing remaining openings.

4. Place the positioning block into the concentrate outlet tube. Then put in the fastening nut. Next, put in the cylinder block and screw in the fastening bolt. [Positioning block, fastening nut, cylinder block and fastening bolt are part of the concentrate tube plug assembly.]

5. Connect the air supply line.

6. Supply oil-free compressed air to the module and slowly raise pressure to 1.5 bars (or 21 psi). 7. Provide a water stream to cover the permeate end of the fibers to help locate any leaks.

8. As the air pressure rises, continuous air bubbles will appear at the location of a broken fiber. Mark the broken fiber with a pin.

9. Continue applying air and water until all broken fibers are located and marked.

10. Depressurize the module using the air release valve.

11. If the broken fibers are near the concentrate tube plug then remove the concentrate tube plug to provide room for repair.

12. Take a new repair pin and place a drop of glue on the end of the pin. Use it to replace the fiber- marking pin immediately. Push the pin firmly into the leaking fiber. Let the repair cure for 5 minutes before trimming the extruding portion of the pin with a knife or diagonal cutters. Repeat for all broken fibers.

13. Repeat steps 4 - 8 to make sure all broken fibers are repaired.

14. To complete the repair, depressurize the membrane, remove the concentrate tube plug, and reassemble the top end cap, remove seals, and realign valves for operation.

You have successfully repaired a Ultrafiltration module!

Calculation of Organic Loading Rate

2009-06-11T08:38:00.001+05:30

Trickling filters are sometimes classified by the organic loading rate applied. The organic loading rate is expressed as a certain amount of BOD applied to a certain volume of media. In other words, the organic loading is defined as the pounds of BOD or chemical oxygen demand (COD) applied per day per 1000 cubic feet of media — a measure of the amount of food being applied to the filter slime.

To calculate the organic loading on the trickling filter, two things must be known: the pounds of BOD or COD being applied to the filter media per day and the volume of the filter media in units of 1000 cubic feet. The BOD and COD contribution of the recirculated flow is not included in the organic loading.

Example:

A trickling filter that is 60 ft in diameter receives a primary effluent flow rate of 0.440 MGD.Calculate the organic loading rate in units of pounds of BOD applied per day per 1000 ft3 of media volume. The primary effluent BOD concentration is 80 mg/L. The media depth is 9 ft.

0.440 MGD x 80 mg/L x 8.34 lb/gal = 293.6 lb of BOD applied/d
Surface area = 0.785 x (60)2 = 2826 ft 2
Area x depth x volume = cu ft
2826 ft2 x9 ft = 25,434 cu ft (TF volume)

What is Chlorine Disinfection?

2009-06-10T06:09:00.001+05:30

CHLORINE DISINFECTION

Chlorine deactivates microorganisms through several mechanisms that can destroy most biological contaminants, including:

Damaging the cell wall
Altering the permeability of the cell (the ability to pass water in and out through the cell wall) • Altering the cell protoplasm
Inhibiting the enzyme activity of the cell so it is unable to use its food to produce energy
Inhibiting cell reproduction.

Chlorine is supplied as a gas, liquid and a solid / Granular / Tablet.

Chlorine as GAS LIQUID SOLID / TABLET

The gas is 100 percent elemental chlorine (Cl2), and is supplied in 150 lb. cylinders (10 inches in diameter and about 55 inches high) and in 2,000 lb. (ton) containers (30 inches in diameter and 82 inches high). The liquid is sodium hypochlorite (NaOCl) commonly used as laundry bleach. And the solid is calcium hypochlorite [Ca(OCl)2], available in granular form or as tablets.

Chlorine is available in a number of different forms: (1) as pure elemental gaseous chlorine (a greenish-yellow gas possessing a pungent and irritating odor that is heavier than air, nonflammable, and nonexplosive), which, when released to the atmosphere, is toxic and corrosive; (2) as solid calcium hypochlorite (in tablets or granules); or (3) as a liquid sodium hypochlorite solution (in various strengths). The strength of one form of chlorine compared to the others that must be used for a given water system depends on the amount of water to be treated, configuration of the water system, local availability of the chemicals, and skill of the operator. One of the major advantages of using chlorine is the effective residual that it produces. A residual indicates that disinfection is completed, and the system has an acceptable bacteriological quality. Maintaining a residual in the distribution system helps to prevent regrowth of those microorganisms that were injured but not killed during the initial disinfection stage.

What is Water Filtration?

2009-06-10T05:17:00.001+05:30

Water filtration is a physical process of separating suspended and colloidal particles from waste by passing the water through a granular material. The process of filtration involves straining, settling, and adsorption. As floc passes into the filter, the spaces between the filter grains become clogged, reducing this opening and increasing removal. Some material is removed merely because it settles on a media grain. One of the most important processes is adsorption of the floc onto the surface of individual filter grains. In addition to removing silt and sediment, flock, algae, insect larvae, and any other large elements, filtration also contributes to the removal of bacteria and protozoans such as Giardia lamblia and Cryptosporidium . Some filtration processes are also used for iron and manganese removal.

The surface water treatment rule (SWTR) specifies four filtration technologies, although SWTR also allows the use of alternate filtration technologies (e.g., cartridge filters). These include slow sand filtration see Figure, rapid sand filtration, pressure filtration, diatomaceous earth filtration, and direct filtration. Of these, all but rapid sand filtration is commonly employed in small water systems that use filtration. Each type of filtration system has advantages and disadvantages. Regardless of the type of filter, however, filtration involves the processes of straining (where particles are captured in the small spaces between filter media grains), sedimentation (where the particles land on top of the grains and stay there), and adsorption (where a chemical attraction occurs between the particles and the surface of the media grains).

FLOW RATE THROUGH A FILTER (gpm)

Flow rate in gpm through a filter can be determined by simply converting the gpd flow rate indicated on the flow meter. The flow rate (gpm) can be calculated by taking the meter flow rate (gpd) and dividing by 1440 min/day, as shown in Equation.

Flow rate gpm=flow rate (gpd) / 1440 min/day

gpm:gallon per minute
gpd:gallon per day

What is Coagulation-Flocculation?

2009-06-08T22:49:00.001+05:30

Coagulation:Following screening and the other pretreatment processes, the next unit process in a conventional water treatment system is mixing, when chemicals are added during what is known as coagulation. The exception to this situation occurs in small systems using groundwater, where chlorine or other taste and odor control measures are often introduced at the intake and are the extent of treatment. The term coagulation refers to the series of chemical and mechanical operations by which coagulants are applied and made effective.

These operations are comprised of two distinct phases: (1) rapid mixing to disperse coagulant chemicals by violent agitation into the water being treated, and (2) flocculation to agglomerate small particles into well-defined floc by gentle agitation for a much longer time. The coagulant must be added to the raw water and perfectly distributed into the liquid; such uniformity of chemical treatment is reached through rapid agitation or mixing. Coagulation results from adding salts of iron or aluminum to the water and is a reaction between one of the following (coagulants) salts and water:

Alum — aluminum sulfate
Sodium aluminate
Ferric sulfate
Ferrous sulfate
Ferric chloride
Polymers

FLOCCULATION:Flocculation follows coagulation in the conventional water treatment process. Flocculation is the physical process of slowly mixing the coagulated water to increase the probability of particle collision. Through experience, we see that effective mixing reduces the required amount of chemicals and greatly improves the sedimentation process, which results in longer filter runs and higher quality finished water. The goal of flocculation is to form a uniform, feather-like material similar to snowflakes — a dense, tenacious floc that entraps the fine, suspended, and colloidal particles and carries them down rapidly in the settling basin. To increase the speed of floc formation and the strength and weight of the floc, polymers are often added.

Weight of Water Related to the Weight of Air

2009-06-08T22:27:00.001+05:30

The theoretical atmospheric pressure at sea level (14.7 psi) will support a column of water 34 feet high:

14.7 psi x 2.31 ft/psi = 33.957 ft, or 34 ft

At an elevation of 1 mile above sea level, where the atmospheric pressure is 12 psi, the column of water would be only 28 feet high: 12 psi x 2.31 ft/psi = 27.72 ft, or 28 ft

If a tube is placed in a body of water at sea level (e.g., a glass, a bucket, a water storage reservoir, lake, pool), water will rise in the tube to the same height as the water outside the tube. The atmospheric pressure of 14.7 psi will push down equally on the water surface inside and outside the tube. However, if the top of the tube is tightly capped and all of the air is removed from the sealed tube above the water surface, forming a perfect vacuum , the pressure on the water surface inside the tube will be 0 psi. The atmospheric pressure of 14.7 psi on the outside of the tube will push the water up into the tube until the weight of the water exerts the same 14.7 psi pressure at a point in the tube even with the water surface outside the tube. The water will rise 14.7 psi x 2.31 ft/psi = 34 feet. In practice, it is impossible to create a perfect vacuum, so the water will rise somewhat less than 34 feet; the distance it rises depends on the amount of vacuum created.

Trickling Filter Process Calculations

2009-06-07T16:42:00.001+05:30

The trickling filter process (see Figure Below) is one of the oldest forms of dependable biological treatment for wastewater. By its very nature, the trickling filter has advantages over other unit processes. For example, it is a very economical and dependable process for treatment of wastewater prior to discharge. Capable of withstanding periodic shock loading, process energy demands are low because aeration is a natural process.

the trickling filter operation involves spraying wastewater over a solid media such as rock, plastic, or redwood slats (or laths).As the wastewater trickles over the surface of the media, a growth of microorganisms (bacteria,protozoa, fungi, algae, helminthes or worms, and larvae) develops. This growth is visible as a shiny slime very similar to the slime found on rocks in a stream. As wastewater passes over this slime,the slime adsorbs the organic (food) matter.This organic matter is used for food by the microorganisms.At the same time, air moving through the open spaces in the filter transfers oxygen to the wastewater. This oxygen is then transferred to the slime to keep the outer layer aerobic. As the microorganisms use the food and oxygen, they produce more organisms, carbon dioxide, sulfates,nitrates, and other stable byproducts; these materials are then discarded from the slime back into the wastewater flow and are carried out of the filter. various process calculations,

Problem
A trickling filter that is 80 ft in diameter treats a primary effluent flow of 550,000 gpd. If the recirculated flow to the clarifier is 0.2 MGD, what is the hydraulic loading on the trickling filter?
Solution

Total Coliforms|Fecal Coliforms|E- Coli-Defines

2009-06-03T08:20:00.001+05:30

Total Coliforms:Coliforms are a group of gram-negative, rod-shaped bacteria that are nonpathogenic and nonspore forming. The most common coliform genera are Escherichia, Enterobacter, Citrobacter,Serratia, and Klebsiella, with E. coli being the most abundant in the gut of humans and other warm-blooded animals. Coliform bacteria are identifiable by their ability to ferment lactose to produce acid and gas within 48 h, when incubated at 35 DegC.

However,the development and use of media and commercial kits to detect coliforms based on specific enzymes (b-galactosidase) have expanded the definition of coliforms to include many genera of bacteria, some of which live primarily in the environment rather than in the gut of warm-blooded animals.Because they are found in the intestines of humans, domestic animals, and wild animals, coliforms are shed in feces along with pathogenic organisms present in the gut of infected animals, and can be detected in water with relative ease; total coliforms have been used by the US Public Health Service since 1914 as the standard for sanitary quality of water. However, because some coliforms occur naturally in soils, aquatic environments including drinking water distribution systems, and plant matter where they can proliferate, and because pathogenic organisms do occur in water and disease outbreaks have occurred even when coliforms are not present, they are neither reliable indicators of fecal contamination nor indicators for the presence of pathogenic microorganisms.

Fecal Coliforms:Fecal coliforms (FC) are a subgroup of total coliforms consisting mainly of E. coli,Enterobacter, and some Klebsiella. They inhabit the intestines of warm-blooded animals.Because they can grow and ferment lactose at a relatively high temperature (Approximate 45.08 Deg C),

Escherichia Coli:Escherichia coli is found in the intestines of humans and other warm-blooded animals where it performs important physiological functions. They are not normally found living in other environments, but have been reported to multiply in surface waters, especially in tropical environments. Several strains of E. coli are usually non disease causing, although illnesses such as septicemia and urinary tract infections have been reported, especially in immuno compromised individuals. Some E. coli strains (e.g., E. coli O157:H7) produce toxins that may cause diarrhea or even death in humans, particularly in elderly people and children
A historical account of the use of E. coli as an indicator bacterium for fecal contamination can be found in Feng et al. E. coli was first proposed as an indicator species in 1892. But, it was only after the development of newer methods for rapid identification and differentiation of the species from the other members of the fecal coliform group that it officially came into use as an indicator species.

Sources of Industrial and Municipal Stromwater

2009-05-29T16:51:00.001+05:30

Sources of Industrial Stromwater.

Any solid or liquid material or chemical stored, leaked or spilled on the ground from an industrial operation can be transported by stormwater to a recovery stream and become a pollutant. These sources can be from any or all of the following: • Outside process areas • Inside process areas which discharge to the outside • Roof drains • Parking lots • Roadways • Loading/unloading areas • Storage areas • Wastewater treatment areas • Soil runoff • Spills • Leaks • Tank farms

Sources Municipal Stormwater:

Any material or chemical deposited on the ground in a municipality can likewise be transported to a receiving stream as a pollutant. These include: • Petroleum product spills and leaks • Garbage and trash • Soil runoff • Surfacing underground sewage disposal systems • Spills and leaks from material or chemical transport

Water Analysis Procedure of Various Species

2009-05-27T21:18:00.001+05:30

Water Analysis Procedure of Various Species | Elements

How Does Ozone (O3) Works

2009-04-22T21:16:00.001+05:30

Ozone operates according the principle of oxidation. When the static loaded ozone molecule (O3) contacts with something “oxidation able”, the charge of the ozone molecule will directly flow over. This is because ozone is very instable and likes to turn back in its original form (O2). Ozone can oxidize with all kinds of materials, but also odor and microorganisms like viruses, moulds and bacteria’s. The extra oxygen atom releases from the ozone molecule and binds with the other material. Eventually remains only the pure and stable oxygen molecule. Ozone is one of the strongest oxidation agents technical available for use to oxidize solutes. The extra-added oxygen atom will bind (=oxidation) in a split second to every component that comes into contact with ozone. Ozone can be used for a broad of area of purification. For the biggest part ozone is applied in the municipal wastewater and potable water treatment plants (for disinfection). However ozone is used more and more in the industrial branch. In the food industry for example ozone is used for disinfection and in the paper- and textile industry it is used for the oxidation of wastewater. The main benefit of ozone is its clean character, because it only oxidizes materials, with forming almost no byproducts. Because ozone has a strong recognizable odor, very low concentrations will soon be perceived. This makes it generally safe to work with ozone.

This is the Picture of Ozone Layer Is Diminishing Rapidly

MEMBRANE TECHNIQUES-Electrodialysis

2009-03-09T06:57:00.001+05:30

Electrodialysis The ions in a water solution can be made to migrate by applying an electric field to the solution. By arranging various barriers to the flow of ions, it is possible to directly desalinate water with electricity. Such barriers are called ion-exchange membranes. Membranes that allow a reasonable flow of cations, but block or reduce the flow of anions, are called cationic-exchange membranes. Membranes that allow a reasonable flow of anions, but block or reduce the flow of cations, are called anion-exchange membranes. Membranes that pass both anions and cations are called neutral membranes. a. Theory. In solutions containing dissolved ions, electric currents are carried by movement of the ions.Positive ions migrate in the direction of the current flow, and negative ions migrate against the current direction.When the anions are blocked by a cationic-exchange membrane, they stop and form a localized charge at the membrane face. This accumulated negative charge is neutralized by the flow of cations across the cationic membrane. This generates a concentrated solution on the side of a cationic-exchange membrane that faces the negative electrode. It also generates a dilute solution on the side of the cationic membrane that faces the positive electrode as shown in figure.
b. Electrodialysis stack. If both a cationic and anionic membrane are placed across a current flow in an electrolyte solution, the side of the cationic membrane facing the positive electrode and the side of the anionic membrane facing the negative electrode will
become less saline. If the cationic membrane is closer to the negative electrode and the anionic membrane is closer to the positive electrode, the solution between the membranes will become less saline as the ions migrate in their respective directions. Any number of pairs of cationic and anionic membranes can be placed across a current-carrying solution, such that the cationic membrane is closest to the negative electrode, and the solution between will be diluted Fig. A battery of several such membrane pairs is called an electrodialysis stack. Several variations of the standard electrodialysis stack have been developed, but none have been proven superior to this standard stack of alternating cationic and anionic-exchange membranes to desalinate natural brackish water

c. Electrodialysis reversal. One important improvement now used in electrodialysis installations is to reverse the polarity periodically and move the ions in the opposite direction. This returns anions across the anionic membranes and helps break up scale formed on the concentrating face of the membranes. Water will flow osmotically across both membranes from the dilute product stream to the concentrated brine stream in an electrodialysis-reversal stack. This osmotic product water loss concentrates uncharged material, such as turbidity and bacteria. This concentration effect must be considered during the design to ensure meeting water turbidity and product water bacterial count requirements.Most electrodialysis membranes are not tolerant of chlorine. When possible, water desalinated by electrodialysis reversal should be disinfected after desalination is completed. The membranes should be protected by a 10-micron cartridge filter.

BIOLOGICAL TREATMENT OF DIFFICULT WASTES

2009-02-25T05:37:00.001+05:30

Toxicity
Things that can cause toxicity include many of the following:
     Metals: lead, antimony, copper, zinc, chromium, cadmium, nickel, manganese
(permanganate), sliver,
    Oxidizers: chlorine, chloramines, any of the group VII compounds in the
periodic table, permanganates, ozone, fluorine, iodine, peroxides, and
so on.
             All of these compounds are direct toxins, because they directly interfere
with the biological cycles in the cell and the cell enzymes.Some organic materials are resistant because they are chlorinated, and chlorination makes them substantially harder to deal with. Others are toxic because they are phenolics. Phenol was the first major disinfectant. It can be biodegraded readily but it takes some work.
The point is that complex organic materials have some ability to biodegrade, if the conditions are correct. However, all biological treatment is as follows: The art of engineering a system so that the bacteria do what they will and want to do in a manner that coincides with your objectives. Stated in another way: ‘‘Given any combination of temperature, pressure, nutrients,and substrate, the bugs will do as they damn well please.’’3 You have to understand what you are treating and how it degrades.
              One of the best sources for information on biodegradability of all organic
compounds is Karl Verschueren’s Book, ‘‘Handbook of Environmental Data on Organic Chemicals,’’ by Van Nostrand Rheinhold, NY. The book is quite complete and has excellent data on biodegradability for specific organic compounds. Much of the rate information in the book is unavailable elsewhere.

Calculation of Bacterial Density

2009-02-17T07:27:00.001+05:30

Calculation of bacterial density.

The determination of indicator bacteria, total coliform, fecal coliform, and fecal streptococcus or enterococcus is very important for assessing the quality of natural waters, drinking-waters, and wastewaters. The procedures for enumeration of these organisms are presented elsewhere (APHA et al., 1995). Examinations of indicator bacterial density in water and in wastewater are generally performed by using a series of four-decimal dilutions per sample, with 3 to 10, usually 5, tubes for each dilution. Various special broths are used for the presumptive, confirmation, and complete tests for each of the bacteria TC, FC, and FS, at specified incubation temperatures and periods. MPN method. Caliform density is estimated in terms of the most probable number (MPN). The multiple-tube fermentation procedure is often

Waste Water Treatment

2009-02-12T04:51:00.001+05:30

1.What is Waste water

“Wastewater,” also known as “sewage,” originates from household wastes, human and animal wastes, industrial wastewaters, storm runoff, and groundwater infiltration. Wastewater, basically, is the flow of used water from a community. It is 99.94% water by weight.The remaining 0.06% is material dissolved or suspended in the water. It is largely the water supply of a community after it has been fouled by various uses.

2.Characteristics of waste water

An understanding of physical, chemical, and biological characteristics of wastewater is very important in design, operation, and management of collection, treatment, and disposal of wastewater. The nature of waste-water includes physical, chemical, and biological characteristics which depend on the water usage in the community, the industrial and commercial contributions, weather, and infiltration/inflow.

3.Physical properties of wastewater

When fresh, wastewater is gray in color and has a musty and not unpleasant odor. The color gradually changes with time from gray to black. Fouland unpleasant odors may then develop as a result of septic sewage. The most important physical characteristics of wastewater are its temperature and its solids concentration. Temperature and solids content in wastewater are very important factors for wastewater treatment processes. Temperature affects chemical reaction and biological activities. Solids, such as total suspended solids (TSS), volatile suspended solids (VSS), and settleable solids, affect the operation and sizing of treatment units.

Solids. Solids comprise matter suspended or dissolved in water and wastewater. Solids are divided into several different fractions and their concentrations provide useful information for characterization of waste-water and control of treatment processes.

Total solids. Total solids (TS) is the sum of total suspended solids and total dissolved solids (TDS). Each of these groups can be further divided into volatile and fixed fractions. Total solids is the material left in the evaporation dish after it has dried for at least 1h or overnight (prefer-ably) in an oven at 103 to 105°C and is calculated according to Standard Methods.

Total suspended solids. Total suspended solids (TSS) are referred to as nonfilterable residue. The TSS is a very important quality parameter for water and wastewater and is a wastewater treatment effluent standard. The TSS standards for primary and secondary effluents are usually set at 30 and 12 mg/L, respectively. TSS is determined by filtering a well-mixed sample through a 0.2 mm pore size, 24 mm diameter membrane; the membrane filter is placed in a Gooch crucible, and the residue retained on the filter is dried in an oven for at least 1h at a constant weight at 103 to 105°C.

Calculation of Chemical Oxygen Demand (C.O.D)

2009-02-05T06:15:00.001+05:30

Calculation of Chemical Oxygen Demand (C.O.D)

Apparatus:

Round bottom flask, water condenser, Burette, Pipette,Heating mantle.

Reagents:

* Mercuric sulphate (< 1gm)

* Sulfuric Acid (1 Kg H₂SO₄ + 5.5 gm Ag₂SO₄ ) dissolve for 24 hrs.

* 0.25 N Potassium Dichromate (12.259 gm K₂Cr₂O₇ dried at 103⁰C + 1 Liter D.W.)

* 0.1 N Ferrous Ammonium Sulphate (39.2 gm Fe (NH₄)₂(SO₄)₂.6H₂O + 20 ml Conc.H₂SO₄ + 1 Ltr D.W.)

* Glass beads.

Procedure

* Wash all the apparatus with distilled water

* Dry the round bottom flask by keeping in oven for 10-15 minute

* Follow the steps as per protocol mentioned below.

Protocol

Reagent Blank Sample

Hg₂SO₄ Pinch Pinch

K₂Cr₂O₇ 10 ml 10 ml

Distilled water 20 ml Sample + D.W = 20 ml

1 Kg H₂SO₄ + 5.5 gm Ag₂SO₄30 ml 30 ml

Note: - for accuracy in results take raw effluent Sample of 0.2 ml to 0.5 ml.

* While adding acid keep the flask in ice bath to avoid loss of volatile Substances due to heat liberation.

* Add 1 – 2 glass beads to avoid the bumping during heating.

* Keep the flask for refluxing for 2 hours.

* Cool the flask thoroughly.

* Titrate with 0.1 N FAS (Ferrous Ammonium Sulphate) using Ferroin indicator

* Continue to titrate till colour turns wine red which is the end point

Calculations:

COD as mg/l of oxygen consumed =(A-B) x Normality of FAS x 8000 / ml. of sample taken

Where

A = ml. of FAS used for titration of blank

B = ml. of FAS used for titration of sample

Standardization of FAS

* 0.05 N Potassium Dichromate

(2.452 gm Anhydrous K₂Cr₂O₇ in 1 Ltr of Distilled water)

* 0.25 N Potassium Dichromate

(12.259 gm Anhydrous K₂Cr₂O₇ in 1 Ltr of Distilled water)

* Whenever a new solution of FAS or Potassium Dichromate is prepared it has to be standardized using Potassium Dichromate as primary Standard.

* Weigh 39.2 gms of FAS and dissolve it in 1000ml of distilled water by adding 20.0ml of concentrated sulphuric acid drop wise by cooling.

* Transfer to 1000ml volumetric flask and dilute it up to mark to get 0.1N FAS solution

* Take 10 ml of 0.25N Potassium Dichromate & 90 ml of distilled water

* Then add 30 ml of concentrated Sulphuric Acid (addition should be done by cooling

Simultaneously)

* Titrate this solution against freshly prepared FAS using Ferroin indicator

* Continue titrating till wine red colour appears which the end point is.

Calculations:-

FAS K₂Cr₂O₇

N₁V₁ = N₂V₂

Where N₁ = Normality of FAS

V₁ = Volume of FAS used for titration of Dichromate

N₂ = Normality of Potassium Dichromate

V₂ = Volume of Potassium Dichromate taken for titration

By putting the above values the Normality of FAS can be calculated

Precision & Bias: For COD of 200mg/lit in absence of chloride the standard

Deviation was found to be + / - 13 mg /lit of O₂ consumed.

Note: * The chief limitation of the COD test is its inability to differentiate between Biologically Oxidisable

And Biologically Inert Organic matter.

* It does not provide any evidence of the rate at which the Biologically active material would be

Stabilized under condition that exists in nature. ( Ref : Page 545 – Perry L. McCarty )

%mixture	Range of BOD	ml. of sample	Range of BOD
0.01	20,000-70,000	0.02	30,000-105,000

0.02	10,000-35,000	0.05	12,000-42,000
0.05	4,000-14,000	0.10	6,000-21,000
0.1	2,000-7000	0.20	3,000-10,500
0.2	1,000-35,000	0.50	1200-4200
0.5	400-1400	1.0	600-2100
1.0	200-700	2.0	300-1,050
2.0	100-350	5.0	120-420
10.0	20-70	20.0	30-105
5.0	40-140	10.0	60-210
20.0	10-35	50.0	12-42
50.0	4-14	100	6-21
100	0-17	300	0-7

(Reference – Table 3-10, Page – 72, Metcalf & Eddy)

Check Procedure for C.O.D.

Lightly crush & Dry Potassium Hydrogen Phthalate at 120⁰C, Dissolve 425mgs in Distilled water and Dilute to 1000ml.
This Solution has a theoretical C.O.D. of 500 ppm.
This solution to be used as sample to cross check the procedure as well as the chemicals being added whether it gives the correct result.

(This solution could be preserved for 3 months under refrigerated condition.)

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Calculation of Total Dissolved Soilds(TDS)

2009-02-01T07:48:00.001+05:30

Calculation of Total Dissolved Solids (TDS) of given water sample.

Apparatus:

Oven, desiccators, filter paper, pipettes.

Procedure:

* Heat clean dish for 1hour in an oven

* Store in desiccators and weigh immediately before use.

* Stir the sample and pipette a measured volume onto a glass fiber filter.

* Wash with three successive 10ml volumes of reagent grade water,Allow complete drainage between washings and continue suction for about 3 min after filtration.

* Collect the filtrate in the weighed dish and dry for atleast 1 hr in the oven at 180⁰C

* Cool in desiccators to balance temperature and weigh.

* Repeat cycle of drying, cooling, desiccating & weighing until a constant Weight is obtained.

Calculation: Total Dissolved Solids, mg /lit = (A-B) x1000 / Sample volume,ml

Where:

A = weight of dried residue + dish

B = weight of empty dish

Coagulation and Flocculation Calculations

2009-01-25T17:49:00.001+05:30

COAGULATION AND FLOCCULATION CALCULATIONS

Calculations are performed during operation of the coagulation and flocculation unit processes to determine chamber or basin volume, chemical feed calibration, chemical feeder settings, and detention time.
CHAMBER AND BASIN VOLUME CALCULATIONS
To determine the volume of a square or rectangular chamber or basin, we use:
Volume (cu ft) = length (ft) x width (ft) x depth (ft)
Volume (gal) = length (ft) x width (ft) x depth (ft) x 7.48 gal/cu ft

Example 16.1
Problem
A flash mix chamber is 4 ft square with water to a depth of 3 ft. What is the volume of water (in gallons) in the chamber?
Solution
Referring to Equation
Volume (gal) = 4 ft x 4 ft x 3 ft x 7.48 gal/cu ft
= 359 gal

Basic Pumping Calculations

2009-01-25T17:30:00.001+05:30

BASIC PUMPING CALCULATIONS
Certain computations used for determining various pumping parameters are important to the water/wastewater operator. In this section, we use basic-pumping calculations relevant to the subject matter.
PUMPING RATES
Important Point:
$The rate of flow produced by a pump is expressed as the volume of water pumped
during a given period.The mathematical problems most often encountered by water/wastewater operators when determining pumping rates are often determined by using Equations

Pumping rate (gpm)=gallons / minutes

Pumping rate (gph)=gallons / hours

Example:
Problem
The meter on the discharge side of the pump reads in hundreds of gallons. If the meter shows a reading of 110 at 2:00 p.m. and 320 at 2:30 p.m., what is the pumping rate expressed in gallons per minute?
Solution
The problem asks for pumping rate in gallons per minute (gpm), so we use Equation
• Step 1: To solve this problem, we must first find the total gallons pumped (determined
from the meter readings).
32,000 gal – 11,000 gal = 21,000 gal
• Step 2: This quantity was pumped between 2:00 p.m. and 2:30 p.m. for a total of 30
minutes. From this information, calculate the gpm pumping rate:

Pumping rate (gpm)=21,000 gal / 30 min
=700 gpm pumping rate

Calculation of Normality

2009-01-25T17:06:00.001+05:30

Calculation of Normality

Equivalent weight (EW) = Molecular weight (MW) / Valency (Z)

Normality (N) =Equivalent weight (EW) / Volume of Solution (1000 ml.)

Meq = Actual weight (W) / Equivalent weight (EW)

Example: Molecular wt of K₂Cr₂O₇ is 294.148 gm

Valency = 6 (because of Cr ^-6)

EW = 294.148/6 = 49.025

N = 49.025/1000 ml = 0.049025.

To make 0.25 N solution:

= 0.25 x EW = 0.25 x 49.025

= 12.256 gm. of K₂Cr₂O₇is required.

Molarity = Molecular Weight, gms / One Liter of Distilled Water

Example

1 M NaCl = 58.5 gm NaCl in 1 Ltr of D.W. = 58500 mg/Ltr

0.5 M NaCl = 29250 mg/Ltr toxic for Bacteria

Food-to-Microorganism Ratio(F/M Ratio)

2009-01-11T18:38:00.001+05:30

Food-to-Microorganism ratio (F/M ratio)

The food-to-microorganism ratio (F/M ratio) is a process control method/calculation based upon maintaining a specified balance between available food materials (BOD or COD) in the aeration tank influent and the aeration tank mixed liquor volatile suspended solids (MLVSS) concentration The chemical oxygen demand test is sometimes used, because the results are available in a relatively short period of time. To calculate the F/M ratio, the following information is required:

Aeration tank influent flow rate (MGD)
Aeration tank influent BOD or COD (mg/L)
Aeration tank MLVSS (mg/L)
Aeration tank volume (MG)

F/M ratio= primary effluent COD/BOD (mg/L) x Flow (MGD) x 8.34 lb/mg/L/MG /MLVSS (mg/L) x aerator volume (MG) x 8.34 lb/mg/L/MG
Example:-

The aeration tank influent BOD is 145 mg/L, and the aeration tank influent flow rate is 1.6 MGD.What is the F/M ratio if the MLVSS is 2300 mg/L and the aeration tank volume is 1.8 MG?

F / M ratio= 145mg/L x1.6 MGD x 8.34 lb/mg/L /MG
2300 mg /L x1.8 MG x 8.34 lb/mg/L/MG
= 0.06 BOD (lb) / MLVSS (lb)

Key Point:
If the MLVSS concentration is not available, it can be calculated if the percent volatile matter (%VM) of the mixed liquor suspended solids (MLSS) is known.
MLVSS = MLSS x % (decimal) volatile matter (VM)
Key Point:
The food (F) value in the F/M ratio for computing loading to an activated biosolids process can be either BOD or COD. Remember, the reason for biosolids production in the activated biosolids process is to convert BOD to bacteria. One advantage of using COD over BOD for analysis of organic load is that COD is more accurate.

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