Organic Chemistry

1. Treatment of Waste Water
Submitted to: Sir Ghulam Mustafa
Submitted by: Hafiz Muhammad Athar Rizwan
09050607-008
BS Chemistry 3rd
Department of Chemistry
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2. Treatment of Waste Water
Waste water treatment is the process of removing contaminants from wastewater and
household sewage, both runoff (effluents) and domestic. It includes physical, chemical, and
biological processes to remove physical, chemical and biological contaminants. Its objective is to
produce an environmentally-safe fluid waste stream (or treated effluent) and a solid waste (or
treated sludge) suitable for disposal or reuse (usually as farm fertilizer). Using advanced
technology it is now possible to re-use sewage effluent for drinking water, although Singapore is
the only country to implement such technology on a production scale in its production of
NEWater.
Wastewater treatment is the process of taking wastewater and making it suitable for discharge
back into the environment. Wastewater can be formed by a variety of activities, including
washing, bathing, and using the toilet. Rainwater runoff is also considered wastewater. No matter
where it comes from, this water is full of bacteria, chemicals, and other contaminants.
Wastewater treatment reduces the contaminants to acceptable levels so as to be safe for discharge
into the environment.
Wastewater is any water that has been adversely affected in quality by anthropogenic influence.
It comprises liquid waste discharged by domestic residences, commercial properties, industry,
and/or agriculture and can encompass a wide range of potential contaminants and concentrations.
In the most common usage, it refers to the municipal wastewater that contains a broad spectrum
of contaminants resulting from the mixing of wastewaters from different sources.
Sewage is correctly the subset of wastewater that is contaminated with feces or urine, but is often
used to mean any waste water. "Sewage" includes domestic, municipal, or industrial liquid waste
products disposed of, usually via a pipe or sewer or similar structure, sometimes in a cesspool
emptier.
The physical infrastructure, including pipes, pumps, screens, channels etc. used to convey
sewage from its origin to the point of eventual treatment or disposal is termed sewerage.
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3. Wastewater or sewage can come from:
Human waste (feces, used toilet paper or wipes, urine, or other bodily fluids), also known
as blackwater, usually from lavatories;
Cesspit leakage;
Septic tank discharge;
Sewage treatment plant discharge;
Washing water (personal, clothes, floors, dishes, etc.), also known as greywater or
sullage;
Rainfall collected on roofs, yards, hard-standings, etc. (generally clean with traces of oils
and fuel);
Groundwater infiltrated into sewage;
Surplus manufactured liquids from domestic sources (drinks, cooking oil, pesticides,
lubricating oil, paint, cleaning liquids, etc.);
Urban rainfall runoff from roads, carparks, roofs, sidewalks, or pavements (contains oils,
animal feces, litter, fuel or rubber residues, metals from vehicle exhausts, etc.);
Seawater ingress (high volumes of salt and micro-biota);
Direct ingress of river water (high volumes of micro-biota);
Direct ingress of manmade liquids (illegal disposal of pesticides, used oils, etc.);
Highway drainage (oil, de-icing agents, rubber residues);
Storm drains (almost anything, including cars, shopping trolleys, trees, cattle, etc.);
Black water (surface water contaminated by sewage);
Industrial waste
industrial site drainage (silt, sand, alkali, oil, chemical residues);
o Industrial cooling waters (biocides, heat, slimes, silt);
o Industrial process waters;
o Organic or bio-degradable waste, including waste from abattoirs, creameries, and
ice cream manufacture;
o Organic or non bio-degradable/difficult-to-treat waste (pharmaceutical or
pesticide manufacturing);
o extreme pH waste (from acid/alkali manufacturing, metal plating);
o Toxic waste (metal plating, cyanide production, pesticide manufacturing, etc.);
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4. o Solids and Emulsions (paper manufacturing, foodstuffs, lubricating and hydraulic
oil manufacturing, etc.);
o agricultural drainage, direct and diffuse.
The composition of wastewater varies widely. This is a partial list of what it may contain:
Water ( > 95%) which is often added during flushing to carry waste down a drain;
Pathogens such as bacteria, viruses, prions and parasitic worms;
Non-pathogenic bacteria;
Organic particles such as faeces, hairs, food, vomit, paper fibers, plant material, humus,
etc.;
Soluble organic material such as urea, fruit sugars, soluble proteins, drugs,
pharmaceuticals, etc.;
Inorganic particles such as sand, grit, metal particles, ceramics, etc.;
Soluble inorganic material such as ammonia, road-salt, sea-salt, cyanide, hydrogen
sulfide, thiocyanates, thiosulfates, etc.;
Animals such as protozoa, insects, arthropods, small fish, etc.;
Macro-solids such as sanitary napkins, nappies/diapers, condoms, needles, children's
toys, dead animals or plants, etc.;
Gases such as hydrogen sulfide, carbon dioxide, methane, etc.;
Emulsions such as paints, adhesives, mayonnaise, hair colorants, emulsified oils, etc.;
Toxins such as pesticides, poisons, herbicides, etc.
Treatment:
There are numerous processes that can be used to clean up waste waters depending on the type
and extent of contamination. Most wastewater is treated in industrial-scale wastewater treatment
plants (WWTPs) which may include physical, chemical and biological treatment processes.
However, the use of septic tanks and other On-Site Sewage Facilities (OSSF) is widespread in
rural areas, serving up to one quarter of the homes in the U.S. The most important aerobic
treatment system is the activated sludge process, based on the maintenance and recirculation of a
complex biomass composed by micro-organisms able to absorb and adsorb the organic matter
carried in the wastewater. Anaerobic processes are widely applied in the treatment of industrial
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5. wastewaters and biological sludge. Some wastewater may be highly treated and reused as
reclaimed water. For some waste waters ecological approaches using reed bed systems such as
constructed wetlands may be appropriate. Modern systems include tertiary treatment by micro
filtration or synthetic membranes. After membrane filtration, the treated wastewater is
indistinguishable from waters of natural origin of drinking quality. Nitrates can be removed from
wastewater by microbial denitrification, for which a small amount of methanol is typically added
to provide the bacteria with a source of carbon. Ozone Waste Water Treatment is also growing in
popularity, and requires the use of an ozone generator, which decontaminates the water as Ozone
bubbles percolate through the tank.
Disposal of wastewaters from an industrial plant is a difficult and costly problem. Most
petroleum refineries, chemical and petrochemical plants have onsite facilities to treat their
wastewaters so that the pollutant concentrations in the treated wastewater comply with the local
and/or national regulations regarding disposal of wastewaters into community treatment plants or
into rivers, lakes or oceans. Other Industrial processes that produce a lot of waste-waters such as
paper and pulp production has created environmental concern leading to development of
processes to recycle water use within plants before they have to be cleaned and disposed of.
The Primary Treatment Process:
1. Screening:
Wastewater entering the treatment plant includes items like wood, rocks, and even dead animals.
Unless they are removed, they could cause problems later in the treatment process. Most of these
materials are sent to a landfill.
2. Pumping:
The wastewater system relies on the force of gravity to move sewage from your home to the
treatment plant. So wastewater-treatment plants are located on low ground, often near a river into
which treated water can be released. If the plant is built above the ground level, the wastewater
has to be pumped up to the aeration tanks (item 3). From here on, gravity takes over to move the
wastewater through the treatment process.
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6. 3. Aerating:
One of the first steps that a water treatment facility can do is to just shake up the sewage and
expose it to air. This causes some of the dissolved gases (such as hydrogen sulfide, which smells
like rotten eggs) that taste and smell bad to be released from the water. Wastewater enters a
series of long, parallel concrete tanks. Each tank is divided into two sections. In the first section,
air is pumped through the water.
As organic matter decays, it uses up oxygen. Aeration replenishes the oxygen. Bubbling oxygen
through the water also keeps the organic material suspended while it forces 'grit' (coffeegrounds,
sand and other small, dense particles) to settle out. Grit is pumped out of the tanks and taken to
landfills.
4. Removing sludge
Wastewater then enters the second section or sedimentation tanks. Here, the sludge (the organic
portion of the sewage) settles out of the wastewater and is pumped out of the tanks. Some of the
water is removed in a step called thickening and then the sludge is processed in large tanks called
digesters.
5. Removing scum:
As sludge is settling to the bottom of the sedimentation tanks, lighter materials are floating to the
surface. This 'scum' includes grease, oils, plastics, and soap. Slow-moving rakes skim the scum
off the surface of the wastewater. Scum is thickened and pumped to the digesters along with the
sludge.
Many cities also use filtration in sewage treatment. After the solids are removed, the liquid
sewage is filtered through a substance, usually sand, by the action of gravity. This method gets
rid of almost all bacteria, reduces turbidity and color, removes odors, reduces the amount of iron,
and removes most other solid particles that remained in the water. Water is sometimes filtered
through carbon particles, which removes organic particles. This method is used in some homes,
too.
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7. 6. Killing bacteria:
Finally, the wastewater flows into a 'chlorine contact' tank, where the chemical chlorine is added
to kill bacteria, which could pose a health risk, just as is done in swimming pools. The chlorine is
mostly eliminated as the bacteria are destroyed, but sometimes it must be neutralized by adding
other chemicals. This protects fish and other marine organisms, which can be harmed by the
smallest amounts of chlorine.
The treated water (called effluent) is then discharged to a local river or the ocean
7. Wastewater Residuals:
Another part of treating wastewater is dealing with the solid-waste material. These solids are
kept for 20 to 30 days in large, heated and enclosed tanks called 'digesters.' Here, bacteria break
down (digest) the material, reducing its volume, odors, and getting rid of organisms that can
cause disease. The finished product is mainly sent to landfills, but sometimes can be used as
fertilizer.
The following consist of a list of wastewater treatment technologies:
1.Activated sludge systems 2.Advanced Oxidation
Process
3.Distillation
1.Activated sludge:
Activated sludge is a process for treating sewage and industrial wastewaters using air and a
biological floc composed of bacteria and protozoans.
The process: The process involves air or oxygen being introduced into a mixture of primary
treated or screened sewage or industrial wastewater (called wastewater from now on) combined
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8. with organisms to develop a biological floc which reduces the organic content of the
sewage.This material, which in healthy sludge is a brown floc, is largely composed of
saprotrophic bacteria but also has an important protozoan flora mainly composed of amoebae,
Spirotrichs, Peritrichs including Vorticellids and a range of other filter feeding species. Other
important constituents include motile and sedentary Rotifers. In poorly managed activated
sludge, a range of mucilaginous filamentous bacteria can develop including Sphaerotilus natans
which produces a sludge that is difficult to settle and can result in the sludge blanket decanting
over the weirs in the settlement tank to severely contaminate the final effluent quality. This
material is often described as sewage fungus but true fungal communities are relatively
uncommon.
The combination of wastewater and biological mass is commonly known as mixed liquor. In all
activated sludge plants, once the wastewater has received sufficient treatment, excess mixed
liquor is discharged into settling tanks and the treated supernatant is run off to undergo further
treatment before discharge. Part of the settled material, the sludge, is returned to the head of the
aeration system to re-seed the new wastewater entering the tank. This fraction of the floc is
called return activated sludge (R.A.S.). Excess sludge is called surplus activated
sludge(S.A.S.) or waste activated sludge(W.A.S). S.A.S is removed from the treatment process
to keep the ratio of biomass to food supplied in the wastewater in balance. S.A.S is stored in
sludge tanks and is further treated by digestion, either under anaerobic or aerobic conditions
prior to disposal.
Many sewage treatment plants use axial flow pumps to transfer nitrified mixed liquor from the
aeration zone to the anoxic zone for denitrification. These pumps are often referred to as internal
mixed Liquor recycle pumps (IMLR pumps). The raw sewage, the RAS, and the nitrified
mixed liquor are mixed by submersible mixers in the anoxic zones in order to achieve
denitrification.
Activated sludge is also the name given to the active biological material produced by activated
sludge plants.
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9. A generalized, schematic diagram of an activated sludge process.
2. Advanced oxidation process:
Advanced Oxidation Processes (abbreviation: AOPs), refers to a set of chemical treatment
procedures designed to remove organic and inorganic materials in waste water by oxidation.
Contaminants are oxidized by four different reagents: ozone, hydrogen peroxide, oxygen, and
air, in precise, pre-programmed dosages, sequences, and combinations. These procedures may
also be combined with UV irradiation and specific catalysts. This results in the development of
hydroxyl radicals. A well known example of AOP is the use of Fenton's reagent.
The AOP procedure is particularly useful for cleaning biologically toxic or non-degradable
materials such as aromatics, pesticides, petroleum constituents, and volatile organic compounds
in waste water [1]. The contaminant materials are converted to a large extent into stable inorganic
compounds such as water, carbon dioxide and salts, i.e. they undergo mineralization. A goal of
the waste water purification by means of AOP procedures is the reduction of the chemical
contaminants and the toxicity to such an extent that the cleaned waste water may be reintroduced
into receiving streams or, at least, into a conventional sewage treatment.
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10. 3. Distillation
Distillation is a method of separating mixtures based on differences in their volatilities in a
boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a
chemical reaction.
Commercially, distillation has a number of applications. It is used to separate crude oil into more
fractions for specific uses such as transport, power generation and heating. Water is distilled to
remove impurities, such as salt from seawater. Air is distilled to separate its components—
notably oxygen, nitrogen, and argon—for industrial use. Distillation of fermented solutions has
been used since ancient times to produce distilled beverages with a higher alcohol content. The
premises where distillation is carried out, especially distillation of alcohol, are known as a
distillery.
Steps in Wastewater Treatment
1. Pretreatment:
i. Coarse Screening:
Often the first step in wastewater treatment is coarse screening to remove large materials (rags,
logs and other large objects) from the wastewater that could interfere with the treatment process.
Coarse screens (also known as bar racks) are made up of vertical or inclined bars with openings
one to three inches wide. These screens are raked cleaned from time to time. Some wastewater
treatment plants have automated equipment that clean the screens automatically. At other plants,
the screens are manually raked.
ii. Grit Chambers:
The next step is to remove smaller objects (such as sand, broken glass, silt and pebbles). If these
objects are not removed, they can damage pumps and other mechanical devices. These objects
also have a tendency to settle in corners and bends, thus reducing flow capacity and eventually
clogging pipes and channels.
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11. Many grit chambers are concrete-lined ponds, similar to swimming pools, where the wastewater
enters one end and leaves at the opposite end. These grit chambers are typically sized so that the
speed of the wastewater flowing through the chamber is kept well below one foot per second.
Flows this slow allow sand- and silt-sized particles to settle out of the wastewater.
Another design that is sometimes used is an aerated grit chamber. In am aerated grit chamber, air
bubbles are injected into a wastewater basin to force a spiral, or rolling, flow. The air bubbles are
supposed to strip organic material off the surfaces of the inert grit, and the grit settles in the
bottom.
Each wastewater treatment plant usually has at least two grit chambers. This allows each one to
be closed for cleaning. Mechanical devices are usually installed to clean each grit chamber.
Normally, the grit is buried in a sanitary landfill.
iii. Comminutors:
Comminutors are mechanical devices with revolving cutting bars. Comminutors are placed
downstream of the grit chambers to cut and shred any remaining solids.
iv. Flow Equalization:
Wastewater seldom flows into wastewater treatment plants at the same rate throughout each day.
In many cities, the greatest flows reaching the wastewater treatment plants arrive mid-morning.
Such uneven flow volumes reduce wastewater treatment plants' efficiency.
To even out these periods of high and low flow, large basins are constructed at some wastewater
treatment plants to store the wastewater flow from peak periods and release it for treatment.
These basins require aeration and mixing to prevent odors and deposition of solids.
2.Primary Treatment:
After screening the solids and removing the grit, the wastewater still contains light organic
suspended solids. Some of these can be removed by gravity in a sedimentation tank. These tanks
are typically twelve feet deep and hold the wastewater for two or three hours. What settles out is
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12. called sludge. The sludge is removed from the primary treatment tank with mechanical scrapers
and pumps. Grease, oil, and other floating substances rise to the top, where they are removed by
surface skimming equipment.
3.Secondary Treatment:
Secondary treatment removes soluble materials that require oxygen for decay, as well as further
removal of suspended solids.
a. BOD:
Many of the pollutants in city wastewater, if not treated and dumped directly into streams, kill
fish and other wildlife by depriving them of oxygen. These pollutants naturally rot, or
decompose, on their own; but require oxygen to do so. These pollutants steal dissolved oxygen
from the water as they decompose, and fish and other aquatic wildlife die from oxygen
starvation.
The amount of these oxygen-stealing pollutants present in wastewater is measured in terms of
biochemical oxygen demand (BOD, pronounced "bee-oh-dee"). BOD is the amount of oxygen,
usually measured in milligrams of oxygen per liter of wastewater, required to decompose the
organic pollutants found in the wastewater.
Because these organic pollutants decompose on their own in the presence of oxygen and
common microorganisms, these pollutants can be decomposed by merely forcing oxygen into the
wastewater and giving these pollutants time to decompose by natural processes. This is the
procedure used in secondary treatment.
The two most common secondary treatment methods are trickling filters and activated sludge.
b. Trickling Filters:
A trickling filter is a bed of coarse stone or perforated plastic material over which wastewater is
sprayed. The most common design is a bed of stones three to ten feet deep inside a large circular
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13. concrete tank. Some tanks are more than 200 feet in diameter. The wastewater is sprayed over
the filter from rotating arms.
As the wastewater trickles through the bed, microorganisms establish themselves on the stone or
plastic surfaces as slime. The wastewater picks up oxygen as it is sprayed over the filter and
passes over these microorganisms. These microorganisms, in the presence of high amounts of
oxygen, feed on the organic materials in the wastewater.
The microbial slime on the filter bed will grow and eventually clog the filter if not washed out.
Thus, the flow from the filter is sent to a sedimentation basin to allow these solids to settle out.
This sedimentation basin is called a secondary clarifier or a final clarifier to distinguish it from
the sedimentation basin used for primary treatment.
c. Activated Sludge:
Activated sludge is another method of providing secondary treatment to wastewater, whereby a
mixture of wastewater and biological sludge (microorganisms) is agitated and aerated. The
biological solids are then allowed to settle out.
The name "activated sludge" comes from the biological mass formed when oxygen (in the form
of air) is continuously injected into the wastewater. In this process, microorganisms are
thoroughly mixed with organics under conditions that stimulate their growth. As the
microorganisms grow and are mixed by the agitation of the air, the individual microorganisms
clump (or flocculate) together to form a mass of microbes called activated sludge. About eight
cubic feet of air are required for every cubic foot of wastewater.
In the activated sludge process, wastewater flows continuously into an aeration tank where air is
injected into the wastewater to mix the wastewater with the activated sludge, and also to provide
the oxygen needed for the microorganisms to break down the organic pollutants. The mixture of
wastewater and activated sludge is called mixed liquor. The mixed liquor flows to a secondary
clarifier (settling tank) where the activated sludge settles out. Some (usually twenty or thirty
percent) of the settled sludge is returned to the aeration tank (and hence is called return sludge)
to maintain a high population of microbes to break down the organics.
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14. Since more activated sludge is produced than is needed for return sludge, the excess sludge is
removed and disposed of.
d. Secondary Clarifiers:
Regardless which method of secondary treatment is used, the end result is a mixture of
microorganisms and partially treated wastewater that is essentially free of dissolved and
suspended organic material. The organic material that was dissolved or suspended in the
wastewater has now been broken down and consumed by these microorganisms. These
microorganisms, while very small, are still large enough to settle out of the wastewater.
Wastewater leaving trickling filters and activated sludge aeration tanks is then sent to secondary
clarifiers (settling tanks) where the microorganisms settle out. At this point, the wastewater
treatment process is nearly completed.
e. Disinfection:
The next step in secondary wastewater treatment is disinfection. In the United States, the most
common method of disinfection is chlorination. Chlorine is injected into the wastewater and the
wastewater is held in a basin for about fifteen minutes to allow the chlorine to react with any
remaining pathogens.
Since chlorine is toxic to fish, the chlorine is often removed from the wastewater as a last step.
The treated wastewater can then be released into a stream.
4. Sludge:
Both the primary and the secondary treatment processes produce large amounts of sludge. Sludge
is commonly disposed of by storing it in a tank (called a digester) where it undergoes anaerobic
digestion. Methane gas is one by-product of anaerobic digestion, which can be burned off or
used as fuel. Another commonly used method of disposal is incineration.
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15. 5. Advanced Wastewater Treatment:
Although secondary treatment can remove over eighty-five percent of the BOD, suspended
solids and nearly all pathogens, sometimes additional treatment is required. Sometimes a higher
level of BOD removal is required. Sometimes other pollutants, such as nitrogen, phosphorus,
non-biological chemical oxygen demand (COD), or heavy metals may be present that require
removal. Besides removing these other pollutants, advanced wastewater treatment (AWT) can be
so effective in removing pollutants that the treated wastewater can be reused. In many parts of
the world, water is too valuable a resource to be thrown away.
Some processes used in AWT include filtration, carbon adsorption, phosphorus removal and
nitrogen removal.
a) Filtration:
Secondary treatment processes are highly effective in reducing the BOD in wastewater.
However, the secondary clarifiers used to settle out microorganisms in the secondary treatment
process are not totally effective. Some of these microorganisms remain in the wastewater after it
leaves the secondary clarifier, and they add BOD since the decay of these microorganisms will
exert its own oxygen demand.
Sand filters, similar to those used for producing drinking water, are sometimes used for
additional removal of microorganisms and other solids. Unlike water treatment sand filters,
however, the filters used in wastewater treatment often use large, lightweight aggregates (such as
coal) at the top to improve efficiency and facilitate cleaning. Partially treated wastewater usually
contains higher concentrations of solids than does water in a water treatment plant, so these
filters must be designed for greater efficiency and for more frequent cleaning.
b) Carbon Adsorption:
Even after secondary treatment and filtration, soluble organics may still be present in the
wastewater. These remaining materials are called refractory organics. The most practical way to
remove refractory organics is by adsorbing them on activated carbon.
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16. Adsorption (not to be confused with absorption) is the accumulation of materials on an interface
(in this case, the liquid/solid boundary layer). Carbon is activated by heating it in the absence of
oxygen. This activation process creates many small pores in each carbon particle. Activation thus
increases the surface area of each carbon particle, making it more effective as an adsorption
agent.
After the adsorption capacity of the carbon has been exhausted, it can be restored by re-heating it
in the absence of oxygen. This process drives off the adsorbed organics, which can be consumed
in an afterburner.
c) Phosphorus Removal:
Phosphorus, in wastewater, is considered a pollutant because it encourages the growth of algae.
Phosphorus removal usually involves the addtion of ferric chloride, alum or lime to the
wastewater, mixing it in a reaction basin, and then sending the mixture to a clarifier to allow the
phosphorus-containing precipitate to settle out.
d) Nitrogen Control:
Nitrogen in any soluble form is a plant nutrient and may need to be removed from the
wastewater to control the growth of algae. In addition, nitrogen in the form of ammonia exerts an
oxygen demand and can be toxic to fish. Nitrogen can be removed from wastewater by both
biological and chemical means. The biological process is called nitrification/denitrification and
the chemical process is called ammonia stripping.
6. Nitrification/Denitrification:
The natural nitrification process can be forced to occur in the activated sludge process by
maintaining a cell detention time of at least fifteen days. Bacteria can convert nitrates into water
and the gases nitrogen and carbon dioxide. Small amounts of organic materials (such as
methanol, or raw or settled sewage) is added to provide a food source for the bacteria for this
denitrification process.
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17. I. Ammonia Stripping:
Nitrogen in the form of ammonia can be removed chemically by raising the pH (often, by adding
lime) to convert the ammonium ion into ammonia, which can be stripped from the water by
blowing large quantities of air through the water.
Waste Water treatment
Stormwater Treatment and Management:
Stormwater treatment includes (1) storage in retention ponds where evaporation and seepage take
place, and diversion to natural or artificial wetlands , where pollutants are removed by
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18. vegetation and sedimentation and water is returned to the atmosphere by evapotranspiration.
These methods take advantage of the ability of natural filtration and biological processes to aid
in restoring water quality. Under certain circumstances, chemicals may also be introduced as
treatment aids.
As noted above, the principal method used for stormwater treatment is storage wherein natural
processes of sedimentation, evaporation, and nutrient removal take place. Because of the large
volumes of water generated by storms, it usually is not practical to divert these waters to
treatment plants such as those used to process municipal and industrial wastewaters. However, a
number of devices can be inserted into stormwater systems to achieve various levels of removal
of solids and other constitutents. These devices employ features of some of the components of
wastewater treatment plants described previously.
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