unit ii. part -b. waste water engineering

7/31/2019 Unit II. Part -b. Waste Water Engineering

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Unit II

a. Pollution engineering: Types of pollution, Air pollution: sources, effects, technology to combat

air pollution and air quality standards. Technology to combat soil pollution: bioremediation, organicfarming. 02 Hrs

b. Waste water engineering: Waste water characteristics, primary water treatment technologies,Secondary water treatment technologies: trickling filter, rotating biological contactor, activated sludge

process, aeration pond and Tertiary waste water treatment technologies: nitrogen removal,

phosphorous removal and disinfection. 02 Hrs

c. Water Resources Management: water recharging, water conservation and management. Drinkingwater standards, water purification technologies: flash evaporation, electrodialysis and reverse osmosis,

production of mineral water. 01 Hrs

WATER POLLUTION

Water is essential for life. Over 97% of water is present in the oceans but being brackish unfit for human

consumption. Only a limited amount of this is available for human use. Triggered by enormous increase inpopulation and shrinking resources per capita availability of water is decreasing. While per capita

availability of water in the U.S.A is 400 litres in developing countries it is only a1/4 or 1/5 th the amount.

Added to the lower availability is the high incidence of pollution of water supplies in the developing

world.

What is water pollution?

A change in the quality of water resulting from human (anthropogenic) activity that is detrimental to

sustenance of life is called water pollution. Polluted water is unfit for human use- drinking, swimming or

fishing. Contamination is a temporary or incidental change in water quality for the same usage as above.

1. Sources of water pollution

a) Point sources: pollutants are discharged from sewers, sewage plants, meat and dairy industries

through pipes at specific points into the discharge waters( stream, pond, lake or ocean)b) Non-point sources: pollutants present in soil are carried away as run offs by rain water into

streams, rivers or oceans at several points

Types of water pollution

They are of four types;

i) Agricultural wastes- Rain water carries them off as run offs from fields and animal farms.Pollution results from agrochemicals such as fertilizers, organic and inorganic

manure/compost, pesticides, hormones and nutrients. Such run offs are rich in nitrogen, organicmatter, phosphorous and pesticides.

ii) Industrial wastes- Waste water discharges from food, paper, leather, and distillery industriesare heavy in terms of organic load. Metallurgical electroplating industries contribute chromium

and cyanide. Chemical industries throw up heavy metals, acids, alkalis, salts, drugs and Nuclear

reactors pose threat due to radioactive chemical. Pesticide industries contribute insecticides,herbicides rodenticides and fungicides Polymer industries contribute to volatile organic

compounds such as vinyl chloride that is carcinogenic.

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iii) Domestic sewage- It is 99% water with 1% solids (dry matter). The solids are made up of 70%

organic and 30% inorganic chemicals( grits, salt metal oxides)

The organic component is made up of 65% protein, 25% carbohydrates and 10% fat/lipids.Besides these it has turbidity due to suspended matter, off or fowl odourous compounds and

pathogens (microorganisms causing disease)

iv) Natural sources / run offs- Run offs from virgin forests (free of human activities) or those

due to earthquakes or cyclones are not considered as pollution. Run offs from villages and urban

areas are markedly different in terms of pollutants.

2. Classification or types of pollutants in water

2.1 Oxygen demanding pollutants

An important criterion for water quality is the dissolved oxygen or DO in the sample which is usually 8 to

15 mg/L. Do is essential for sustenance of aquatic life. Minimum DO required for aquatic life is 5 mg/L.

Polluted waters are heavily loaded with organic matter which get oxidized in natural water bodies anddeplete the DO content. This leads to anaerobic condition, eventually death of all the aquatic life. This

Oxygen demanding pollutants is a mixture of number of chemical which is measured and represented bytwo parameters

a) Biochemical oxygen demand (BOD), and

b) Chemical oxygen demand (COD)

a. Biochemical oxygen demand (BOD),BOD is defined as the amount of oxygen required by microorganisms to decompose or oxidize organicmatter in the waste water under aerobic (in presence of air or oxygen) conditions producing CO2 and H2O

and non objectionable stable products.

Microorganisms (aerobic decomposition)Organic matter + O2 ---------------------------------- CO2 + H20 + New cells + stable products such

as N03, PO4, SO4

Under conditions of insufficient oxygen supply the decomposition of organic matter is brought about by anentirely different group of microorganisms producing unstable odourous products

Microorganisms (anaerobic decomposition)Organic matter + O2 -------------------------------- CO2 + H20 + New cells + unstable products

( H2S, NH3, CH4 etc)

BOD Test: The total amount of O2 required for decomposition or biodegradation of organic matter inwaste water or polluted water is of prime concern in assessing the impact of discharging the water sample

into the receiving body of water.

The time required for complete oxidation would be too long to be practicable. Hence a 5-day BOD test isdone at 200C which is the total O2 consumed by microorganisms in the sample during the first five days of

biodegradation which is represented as BOD5 200C.

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Test is performed by placing a sample of waste water in a 300 ml standard well stoppered BOD bottle

preferably coated black to prevent access to sunlight(Why?. Because access to photosynthesis will result in

release of oxygen and affect BOD values) The sample is diluted to 300 ml with pure water and the mix iswell aerated to incorporate as much O2 as possible. The amount of dissolved O2 is measured at the

beginning of the experiment and after five days incubation at 200C.by using the O2 electrode or by

titration.

BOD5 = DOi - DOf/ P,where,

DOi = initial DO of the sample,DOf = final DO after 5days, and

P = Dilution fraction = Volume of sample / volume of sample + volume of dilution water.

Problem

A 10 ml sample of waste water was mixed with enough water to fill a 300 ml, BOD bottle. The initial DOwas 9mg./l and final DO after 5days at 20 0Cwas 2mg./L Calculate BOD5 20

0C.

BOD5 = DOi DOf / P = (9 2) mg/L / 10/300,

= 210mg./LRelease of such waters with very high BOD into a stream would kill all aquatic life.

b. Chemical oxygen demand (COD)It is the quantity of oxygen required to chemically oxidize the dissolved organic matter in water. It

requires less time to perform compared to BOD test. Oxidation is brought about by potassium dichromate.The sample is treated with known amount of dichromate, acidified and boiled for two hours and cooled.

The organic matter is oxidized by consuming dichromate.

Catalyst, heat

( CaHbOc) + Cr2O7 + H+ -------------- Cr3

+ + CO2 +H20The remaining/residual amount of dichromate is measured by titration with ferric ammonium sulphate.

The difference between the added and the remaining dichromate gives the COD value.

COD test is useful in cases of samples containing toxic compounds that are harmful to microorganisms or

compounds that are non biodegradable such as phenols, benzene, tannic acid and acid pesticides or that are

slowly biodegradable such as cellulose, lignocelluloses, etc.

Generally COD values are higher than BOD5 values (Why). Typical untreated domestic waste water has a

COD / BOD values of 1.5 to 2.5 and a higher ratio will mean that the waste water is difficult to

biodegrade.

2.2 PathogensPathogens are disease-causing organisms. Primary hosts are human beings that harbour these organisms intheir intestinal tract. Many have had such infections and recovered but act as carriers of the disease

without showing any symptoms. Infected persons or carriers shed these pathogens in their stools andthrough hands which ultimately find their way into drinking water supplies causing severe epidemics.

They enter the human body through the water taken in, grow or multiply in the host(man) resulting in

disease or infection.

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decomposition contribute to the colour, turbidity, odours and objectionable tastes of water which are

difficult to remove, thereby decreasing its acceptability as a source of good drinking water.

Three important nutrients required for growth of aquatic species are: carbon, nitrogen and phosphorus in

relatively large amounts. Carbon is readily available from various sources e.g., alkalinity (HCO3, CO3),

dissolved CO2 (from atmosphere) and decaying organic matter and so it is not a limiting nutrient. It isusually nitrogen or phosphorus that controls algal growth and therefore they are called limiting nutrients.

Sources of nitrogen are municipal waste water, water discharges from agricultural land and nitrogendeposition from atmosphere as acid rain especially near power plants. Certain microorganisms

(cyanobacteria and nitrogen fixing bacteria) can take nitrogen from air directly and form ammonia. Some

nitrogen may be present in water as nitrate which gets reduced to nitrite by certain bacteria present in

waters. Nitrate combines with haemoglobin molecule with greater affinity than oxygen resulting in adisease called methemoglobinemia, commonly referred to as blue baby.

Limiting nutrient is phosphorus which enters waters from human faeces and laundry detergents, mainly as

sodium tri-polyphosphate (STP - Na5 P3 O10). These slowly releases orthophosphate ion, PO43-

:P3O105- + 2H2O 3PO4

3- + 4H+

Orthophosphate is a form of phosphorus that can be directly assimilated by plants which begins to actimmediately as it is released as a fertilizer. Use of phosphorus is banned by several countries in view of its

environmental impact.

2.4 SaltsAs water flows through soils and rocks it accumulates a variety of dissolved solids or salts on its way to

the sea. Salts include cations- Na, Ca, Mg, K and anions Cl, SO4, HCO3. Careful measurement of

concentration of these ions gives an idea of the salinity of water. However, a simpler and more commonlyused measure of salinity is the concentration of total dissolved solids or TDS.

TDS values of waters are as follows:

Type of water TDS mg/L

Fresh water < 1500Brackish (salty) water 5000

Sea water 30,000 34000Drinking water < 500

Source of salt in water: Mainly two sources- a) From urban runoffs and industries and,

b)Removal of fresh water by evaporationIn reservoirs, ponds and tanks as water evaporates salts are left behind and there is less fresh water

available to dilute the sample. Irrigated agriculture especially in arid areas is vulnerable to accumulation of

salt due to evaporation.

2.5 Thermal pollution

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Power plants generate tremendous amounts of heat from their cooling towers. A typical nuclear plant

could warm 150,000 m3/hr of cooling by 100C as it passes through the condenser. If such warm water is

dumped into a lake or river the resulting rise in temperature would affect all life in the vicinity. Somefishes such as trout and salmon such temperature increases would spell disaster while for some others

exposure to warm water could be beneficial.

Another important aspect of thermal pollution is the increase in growth rate at higher temperatures causing

an increase in BOD and a lowering of DO.

2.6 Heavy metalsHeavy metals are those having specific gravity greater than 4 or 5. In terms of environmental impact

important heavy metals are mercury(Hg), lead(Pb), cadmium(Cd) and arsenic(As).Metals may be inhaled as vapour or ingested (swallowed). Liquid mercury is not very toxic as most of

what is ingested is excreted from the body. Mercury vapour, on the otherhand, is highly toxic. When

inhaled the vapour is absorbed into the blood stream in the lungs and reaches the brain causing severe

damage to the central nervous system. In contrast lead vapour is not harmful but is most dangerous when

ingested in its ionic form Pb2+

. Heavy metals cause kidney damage. Cadmium, lead and mercury arenephrotoxic metals. Metals can exist in three forms: elemental form, salt form and organic form (bound to

organic compounds) and nowadays all forms of these metals are considered hazardous when present inhigh levels (beyond what is approved by authorities).

2.7 PesticidesThe U.S Environmental Protection Agency defines pesticides as any substance or mixture of substances

intended for preventing, destroying, repelling or mitigating any pest. A pest is a living organism that are

found where they are not wanted or that causes damage to crops, or humans or other animals. The termcovers insecticides, herbicides weedicides, rodenticides, fungicides etc. Some examples:

- Insecticides: Organochlorines (Chlorinated hydrocarbons) e.g., DDT (para dichloro diphenyltrichloro ethane

- Organophosphates e.g., Parathionmalathion, diazinon etc,

- Carbamates e.g., Propoxur, Carbaryl and Aldicarb

Organochlorines are an environmental hazard because they persist in the enviromment for long and so

their bioaccumulation increases to dangerous levels to render species extinct.

Organophosphates are not persistent but are readily absorbed through the skin, lungs and gastro-intestinal

tract. Symptoms include tremors, slurred speech, muscle twitching abnd convulsions.

Carbamates are short lived and do not accumulate in the food chains, but have high human toxicity e.g.,Propoxur, Carbaryl and Aldicarb. Symptoms are: nausea, vomiting, blurred vision, convulsions and death

in extreme instances.

2.8 Volatile organic compoundsIn ground water they are the most commonly found pollutants. These chemicals are used as solvents in

industrial processes. A number of them are known carcinogens or mutagens. Because they are volatile they

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are not found in more than a few g/L in surface waters, but in ground waters concentration can be

hundreds or thousands of times higher.

Five volatile organic compounds are of concern.

Vinyl chloride: carcinogen. Used in the production of polyvinyl chloride resin.

Tetrachloroethylene: used as a solvent, heat transfer medium and in the manufacture of

chlorofluorocarbons. Causes tumours in animals. No evidence of carcinogenicity in humans. Mostcommonly found VOC in ground water.

Trichloroethylene: Used as a solvent to clean electronic parts to jet engines and septic tanks. A

suspected carcinogen.

1,2 Dichloroethane: Used as a metal degreaser in the manufacture of fumigants, varnish removers

and soap compounds. Not a carcinogen but high doses can affect central nervous system, liver and

kidneys. Common ground water contaminant. Quite soluble and hence difficult to remove bystripping.

Carbon tetrachloride: Used in grain fumigants, fire extinguishers and as a Solvent. Toxic when

ingested, a few ml can produce death. Relatively insoluble so only occasionally found in groundwater

2.9 RadionuclidesRadioactive compounds or radionuclides can occur as pollutants in waters. Their levels in drinking water

is regulated by Safe Drinking Water Act. Radon and radium-226 are nuclides commonly found in ground

water, while Sr-90 and Tritium are surface water contaminants resulting from atmospheric nuclear tests.The hazard comes not from drinking radon contaminated water but from breathing the gas generated after

heating such as in a shower or in a washing machine. Inhaled radon gas is an important cause of lung

cancer.

2.10 Oil pollutantsPetroleum products often contaminate water supplies due to oil spills resulting from tanker collisions,

leakages from engines of ships and boats and automotive wastes. They are toxic to aquatic life.

2.11 Summary of effects of water pollution1. Pollutants impart colour, off-odour and off-taste to water rendering it unfit for consumption.2. Organic matter causes a decrease in DO affecting aquatic life.

3. Release of nutrients into waters leads to eutrophication and algal blooms. Shell fish feeding on

toxic algae have caused paralytic shell-fish poisoning.4. Pathogens as pollutants lead to gastroenteritis and dysentery.

5. Heavy metals cause nephro toxicity.

6. Presence of pesticides,VOC and radio nuclides are harmful; in drinking water supplies and aquatic

life.

3. Sewage treatment Water after use becomes sewage or waste water.

Sewage includes all waste waters- from toilets, kitchen and laundry washings, rain water flowing

into municipal drains, industrial wastes from citi drains etc.

Municipal wastewater is 99.9 % water , balance made up of suspended and dissolved solids:Total solids = Total suspended solids + Total dissolved solids

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(suspended solids can be removed by filtration ,while total dissolved solids cannot be removed

In large metropolitan cities this small percentage of solids

may account for more than 1000tons of solids per day.

Such waste waters or sewage cannot be discharge into rivers and oceans due to its very high BOD.

And are therefore treated to reduce BOD to manageable levels that does little harm to theecosystem of our environment.

3.1 Sewage treatmentTreatment comprises of:

1) Primary treatment: Based on physical properties of the contaminants and the water2) Secondary treatment: relays on biological processes, and

3) Tertiary treatment or advanced treatment: a combination of chemical and biological processes.

3. 1 Primary treatment

Involves following steps:

Raw sewage

Screening

Grit chamber

Primary settling tank

Screening is to remove large floating objects(rags, sticks, leaves, plants, small paper boxes,

cups etc) to prevent clogging of pipe lines and damage to pumps.

Sewage flows into a grit chamber where oil and greasy material can be removed.

Flow rate of the sewage is now reduced as it enters the primary settling tank. Suspended

solids settle by gravity. Detention times are 2 3 hrs. In this step 50 -65% suspended solids and25- 40 % BOD is removed. Solids that settles down called sludge is collected for further

processing.

3. 2 Secondary treatment

Objective of secondary treatment is to further remove BOD and suspended solids beyond what is

achievable by primary settling tank. Depends on the number of microbes and the residence time available for microbes to consume the

contaminants

There are following designs to optimize the treatment

a) Trickling filters

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Consist of large circular tanks filled with a bed of fist sized rocks or moulded plastic. A circularly

rotating arm sprays the treated sewage over the bed of rocks. The spaces between the rocks allowenough air to circulate and maintain aerobic conditions.

Microorganisms in the sewage utilize or decompose organic matter in presence of air and grow

forming a biofilm on the rocks. The biofilm is actually a slimy layer that consists of mostly

bacteria, although other organisms such as fungi, algae, protozoa, worms, insect larvae and snailsmay also be present.

The accumulated slime (biofilm) on the rocks occasionally slides off the rocks and settles at the

bottom forming sludge.

The sludge along with the treated waste water enters the secondary settling tank. The sludge settles

down and is removed.

Trickling filters remove 80 85 % of BOD. Although less effective than Activated sludge process,it is less troublesome. However, flow rate must be controlled since with slowing of the rate of

flow, the film on the rocks may dry up reducing the efficiency of the process. (Note that there is

actually no filtration here; the word trickling filters is a misnomer).

b. Rotating Biological contactors (RBC) It consists of a series of plastic discs 3.6 m diam mounted on a central shaft.(Fig.3)

The discs rotate slowly with their lower 40% portion submerged in the pretreated waste water or

sewage. Biofilms, mostly of bacteria, develop on the discs.

As the discs rotate the biofilms in the submerged portion absorb the organic nutrients and when the

discs are not submerged they are exposed to O2 and the biofilm will oxidize the organic matter andreduce BOD.

By employing several RBCs in series reduction of BOD to levels exceeding that obtained in

conventional Trickling filters can be achieved.

c) Activated sludge process

The key to the process is the aeration tank.

The treated waste water from the primary settling tank enters the aeration tank along with a mass

of sludge from the secondary settling tank. The sludge contains a large number of active aerobic

sewage(organic matter) metabolizing organisms that decompose sewage to H20 and CO2. Hencethe name activated sludge process. Bacteria belonging to the family Zoogloea are important

members of the community of organisms in the sludge. These organisms grow in the aeration tank

forming a fluffy, slimy and flocculant biomass, called zoogloeal mat. The organic matter in thesewage is incorporated into the zoogloeal mat which settles down. More organic matter is removed

by this settling process than by the oxidation process in Trickling filters.

Aeration is usually done for 4-8 hrs.

From the aeration tank the floc plus the treated sewage is taken to settling tanks where the flocsettles down. The treated sewage or effluent is disinfected with chlorine and discharged.

d) Oxidation ponds

These are large, shallow ponds, 1 to 2 m deep. Raw or partially treated sewage is fed into theseponds, where it is decomposed by microorganisms.

The decomposition taking place near the surface of the ponds is aerobic, while that near the

bottom is anaerobic. Algae growing near the surface generate oxygen as a result of photosynthesiswhich aids in aerobic decomposition.

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Lagoons are deeper ponds which are mechanically agitated by paddle type wheels.

Ponds are easy to build and manage and their efficiency matches that of conventional biological

treatments (TF or ASP) but at lower cost.

While raw sewage can be directly taken to oxidation ponds, the effluent may not meet the EPA

secondary treatment guidelines of BOD5 of 30mg/L and presence of suspended solids(algae).

They are simple and very effective in destroying pathogenic microorganisms, making these pondsespecially useful in developing countries.

However, it is best to use them to augment secondary treatment, in which case they are calledpolishing ponds.

3.3 Tertiary treatment

Primary and secondary treatments do not remove all the biologically degradable organic matter.For instance, effluent from secondary treatment may contain ~50% of the organic matter and 70 %

of the original phosphorus. Discharging such an effluent into a lake or river would prove

catastrophic to aquatic life.

Tertiary treatment is given to remove nitrogen and phosphorus nutrients from the effluent.

Nitrogen removalOnly about 30% N2 is removed in secondary treatment. Organic N2 is broken down to ammonia bymicroorganisms and to remove ammonia it has to be oxidized which requires O2, which in turn

creates a decrease DO. To avoid these O2 depletion and eutrophication problems, treatment plants

have to be provided with additional facilities to achieve higher rates of N 2 removal.

Overall process for N2 removal is achieved by nitrification / denitrification as follows:

Nitrosomonas

NH4 + 2O2 -------------------- NO2- + 2 H2O

Nitrobacter

2NO2- +O2 ---------------------- 2NO3-

Anaerobic denitrifying bacteria

2NO3- + organic matter ---------------- N2 + CO2 + H2O

Organic matter is converted to harmless N2 gas.

Phosphorus removal

70% P is still present in the effluent after primary and secondary treatment. In biological materials

all P gets converted to ortho phosphate, PO43-.

Phos[phate is removed by precipitation with alum, [Al2(SO4)3] or lime, Ca(OH)2 forming AlPO4

or Ca3(PO4)2.

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contact with water. Handling the solid, however, requires greater routine human contact through opening

bags and pouring than the use of gas cylinders or bleach which are more easily automated. The generation

of liquid sodium hypochlorite is both inexpensive and safer than the use of gas or solid chlorine. All formsof chlorine are widely used despite their respective drawbacks. One drawback is that chlorine from any

source reacts with natural organic compounds in the water to form potentially harmful chemical by-

products trihalomethanes (THMs) and haloacetic acids (HAAs), both of which are carcinogenic in largequantities and regulated by the United States Environmental Protection Agency (EPA) and the Drinking

Water Inspectorate in the UK. The formation of THMs and haloacetic acids may be minimized by

effective removal of as many organics from the water as possible prior to chlorine addition. Althoughchlorine is effective in killing bacteria, it has limited effectiveness against protozoa that form cysts in

water (Giardia lamblia and Cryptosporidium, both of which are pathogenic).

4.2 Ozone disinfection

O3 is an unstable molecule which readily gives up one atom of oxygen providing a powerful oxidizingagent which is toxic to most waterborne organisms. It is a very strong, broad spectrum disinfectant that is

widely used in Europe. It is an effective method to inactivate harmful protozoa that form cysts. It also

works well against almost all other pathogens. Ozone is made by passing oxygen through ultraviolet light

or a "cold" electrical discharge. To use ozone as a disinfectant, it must be created on-site and added to thewater by bubble contact. Some of the advantages of ozone include the production of fewer dangerous by-

products (in comparison to chlorination) and the lack of taste and odour produced by ozonisation.Although fewer by-products are formed by ozonation, it has been discovered that the use of ozone

produces a small amount of the suspected carcinogenbromate, although littlebromine should be present in

treated water. Another of the main disadvantages of ozone is that it leaves no disinfectant residual in thewater. Ozone has been used in drinking water plants since 1906 where the first industrial ozonation plant

was built inNice, France. The U.S. Food and Drug Administration has accepted ozone as being safe; and

it is applied as an anti-microbiological agent for the treatment, storage, and processing of foods.

4.3 Ultraviolet disinfection

Ultraviolet light is very effective at inactivating cysts, in low turbidity water. UV light's disinfection

effectiveness decreases as turbidity increases, a result of the absorption, scattering, and shadowing caused

by the suspended solids. The main disadvantage to the use of UV radiation is that, like ozone treatment, itleaves no residual disinfectant in the water; therefore, it is sometimes necessary to add a residual

disinfectant after the primary disinfection process. This is often done through the addition of chloramines,

discussed above as a primary disinfectant. When used in this manner, chloramines provide an effectiveresidual disinfectant with very few of the negative aspects of chlorination.

4.4 Solar water disinfection

One low-cost method of disinfecting water that can often be implemented with locally available materials

is solar disinfection (SODIS). Unlike methods that rely on firewood, it has low impact on the environment.

One recent study has found that the wild Salmonella which would reproduce quickly during subsequent

dark storage of solar-disinfected water could be controlled by the addition of just 10 parts per million of

hydrogen peroxide.[13]

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http://en.wikipedia.org/wiki/Trihalomethanehttp://en.wikipedia.org/wiki/Haloacetic_acidhttp://en.wikipedia.org/wiki/Carcinogenichttp://en.wikipedia.org/wiki/United_States_Environmental_Protection_Agencyhttp://en.wikipedia.org/wiki/Drinking_Water_Inspectoratehttp://en.wikipedia.org/wiki/Drinking_Water_Inspectoratehttp://en.wikipedia.org/wiki/Giardia_lambliahttp://en.wikipedia.org/wiki/Cryptosporidiumhttp://en.wikipedia.org/wiki/Ozonehttp://en.wikipedia.org/wiki/Chlorinationhttp://en.wikipedia.org/w/index.php?title=Ozonisation&action=edit&redlink=1http://en.wikipedia.org/wiki/Bromatehttp://en.wikipedia.org/wiki/Brominehttp://en.wikipedia.org/wiki/Nicehttp://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiationhttp://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Scatteringhttp://en.wikipedia.org/wiki/Solar_disinfectionhttp://en.wikipedia.org/wiki/Firewoodhttp://en.wikipedia.org/wiki/Hydrogen_peroxidehttp://en.wikipedia.org/wiki/Water_purification#cite_note-12http://en.wikipedia.org/wiki/Water_purification#cite_note-12http://en.wikipedia.org/wiki/Trihalomethanehttp://en.wikipedia.org/wiki/Haloacetic_acidhttp://en.wikipedia.org/wiki/Carcinogenichttp://en.wikipedia.org/wiki/United_States_Environmental_Protection_Agencyhttp://en.wikipedia.org/wiki/Drinking_Water_Inspectoratehttp://en.wikipedia.org/wiki/Drinking_Water_Inspectoratehttp://en.wikipedia.org/wiki/Giardia_lambliahttp://en.wikipedia.org/wiki/Cryptosporidiumhttp://en.wikipedia.org/wiki/Ozonehttp://en.wikipedia.org/wiki/Chlorinationhttp://en.wikipedia.org/w/index.php?title=Ozonisation&action=edit&redlink=1http://en.wikipedia.org/wiki/Bromatehttp://en.wikipedia.org/wiki/Brominehttp://en.wikipedia.org/wiki/Nicehttp://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiationhttp://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Scatteringhttp://en.wikipedia.org/wiki/Solar_disinfectionhttp://en.wikipedia.org/wiki/Firewoodhttp://en.wikipedia.org/wiki/Hydrogen_peroxidehttp://en.wikipedia.org/wiki/Water_purification#cite_note-12

unit ii. part -b. waste water engineering

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