Download As for choosing whether or not to carry on recycling waste water

Report on:
Waste water treatment
Submitted to:
Dr. Sahar Mohamed El Marsafy
Chemical Engineering Department
Faculty of Engineering Cairo University
Prepared by:
Name:
Amr El-sayed Ahmed
Bassam Amr Ibrahim
Dina Atef Shehata
Mai Galal Moawad
Serag Saaid Sabery
Sherif Ezz El-din
Sherif Magd El-din
section:
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June , 2009
B.N:
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Table of contents
Summary
List of figures
List of tables
Aim of work
1. Introduction
1.1 drinking water treatments
1.2 industrial waste water treatments
2. Drinking water treatment
2.1 treatment and conditioning
2.2 water treatment steps
2.3 disinfecting water
2.4 emergency disinfection measures
2.5 ultraviolet light disinfection
2.6 distillation disinfection
2.7 filtration
2.8activated carbon filtration
2.9 oxidizing filtration
2.10 neutralization filtration
2.11 reverse osmosis
2.12 fiber filters
2.13 water softeners
3 industrial water treatment
3.1 treatment of industrial waste water
3.2 solid removal
3.3 oils and grease removal
3.4 removal of biodegradable organics
3.5 activated sludge process
3.6 trickling filter process
3.7 treatment of other organics
3.8 treatment of acids and alkalis
3.9 treatment of toxic materials
References
page
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III
III
IV
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I
 Summary
Water is extremely vital for man-kind, either for daily usage or
in industrial processes; regarding limited water supplies Water
treatment is necessary to acquire maximum benefit of available
water.
Various processes of water treatment are used to remove existing
contaminants from the used water:
Drinking water treatment helps ensuring health and safety,
Industrial waste water treatment is used to reduce and filter
harmful contaminants before unleashing in the public sewer
system.
No water is 100 percent pure. It contains contaminants from
natural and man-made sources, such as minerals, gases, bacteria,
metals and chemicals. Many of these contaminants are harmless.
However, some impurities can adversely affect your health. Others
damage equipment, stain laundry and fixtures and emit odors.
And for the treatment of water for drinking and day using
purposes, the process should be carried in a manner that insure the
complete removal of any harmful impurities, that can have bad
effects on public health, as mentioned above, no water is 100
percent pure, but the report presented, stood on many methods that
can be used to guarantee producing pure water safe to be used for
drinking and daily activities.
II
List of figures and tables :
Figures:
page
Fig.1 API
18
Fig.2 Typical parallel plate separator
19
Fig.3
19
Fig.4 & Fig.5 trickling filter
21
Tables:
Table 1 Typical Water Quall Problems and Recommended
Treatment Systems (page .12)
Table 2 Recommended Amounts of Laundry Bleach for Well
Disinfection Height of standing (page. 13)
III
 Aim of Work
Effort is boosted towards studying state of the art in waste
water treatment, and the drinking water treatment, and to
show both methods and techniques used for each case, also
to stand on the most reliable data and figures that show
how each method work.
As for choosing whether or not to carry on recycling waste
water from industrial sources, it’s very important for any
industrial unit or plant, to investigate the probability of
reusing the waste water resulting from the industrial
process, and through further search and analysis,
calculating coast and benefits, reusing waste water can
become effective for the whole process, and help save any
nearby natural water sources.
And for the treatment of water for drinking and day using
purposes, the process should be carried in a manner that
insure the complete removal of any harmful impurities, that
can have bad effects on public health, as mentioned above,
no water is 100 percent pure, but the report presented, stood
on many methods that can be used to guarantee producing
pure water safe to be used for drinking and daily activities.
IV
1. Introduction
In a modern society, water is one of the things in life we often
take for granted. When we turn on the tap, we expect water that
is clean, safe and suitable for all household tasks. But in recent
years, there has been a growing concern about contamination of
our water supplies. We hear unsettling news accounts that make
us question the safety of our water.
This publication provides a few guidelines for deciding whether
you need to install a home water treatment system, and if so,
how to select a system appropriate to your specific need.
1.1. DRINKING WATER TREATMENT
No water is 100 percent pure. It contains contaminants from
natural and man-made sources, such as minerals, gases, bacteria,
metals and chemicals. Many of these contaminants are harmless.
However, some impurities can adversely affect your health. Others
damage equipment, stain laundry and fixtures and emit odors.
The first step in eliminating exposure to water-borne contaminants
is to assess your situation. If your water comes from a public or
municipal system, it is regularly tested for contaminants regulated
by federal and state standards, such as microbial pathogens,
radioactive elements and certain toxic chemicals. These are the
contaminants that affect the safety of water and may cause health
problems. Since public and municipal systems are regulated, a
home water treatment system is seldom needed for health
protection. Water quality problems such as hardness, corrosively,
foaming, staining or bad tastes, smell or color are undesirable.
However, these factors do not necessarily make the water
unhealthful.
1
1.2. Industrial wastewater treatment
It covers the mechanisms and processes used to treat waters that
have been contaminated in some way by anthropogenic
industrial or commercial activities prior to its release into the
environment or its re-use.
Most industries produce some wet waste although recent trends in
the developed world have been to minimize such production or
recycle such waste within the production process. However, many
industries remain dependent on processes that produce wastewaters
2
2. DRINKING WATER TREATMENT
Methods used to improve the quality of water are referred to as
treatment or conditioning. What is the difference? Water treatment
refers to systems that reduce harmful contaminants in the water,
dealing with health and safety of the water. High levels of
coliform, nitrates, arsenic, lead and pesticides are examples of
harmful contaminants that must be treated before water is safe to
drink.
2.1. Treatment and Conditioning Systems
Water conditioning refers to water problems that effect water taste,
color, odor, hardness and corrosivity rather than health and safety.
The presence of high levels of magnesium, calcium, iron,
manganese and silt are common contaminants that require water
conditioning. It is not uncommon to use both treatment and
conditioning methods to improve water quality.
Here is a list of possible treatment and conditioning methods:
 Mechanical or Sedimentation Filtration
 Activated Carbon Filtration
 Oxidation Filtration
 Neutralizing Filtration
 Reverse Osmosis or Membrane Filtration
 Distillation
 Ultra-violet Treatment
 Water Softener or Cation Exchange
 Chlorination Disinfection
3
2.2. Water Treatment Steps
1. Have water tested.
2. Remove fine sand, silt, clay and other particles, using a
mechanical filter or sedimentation.
3. Treat bacterial contamination, using chlorination or other
forms of disinfection.
4. Remove hydrogen sulfide gas and other odor-causing
substances, using chlorination, an oxidizing filter, or
activated carbon.
5. Remove insoluble iron and manganese particles using a
mechanical filter; a water softener, for small amounts of
dissolved iron and manganese; an oxidizing filter for higher
amounts of dissolved iron and manganese; or a chlorinator
followed by a mechanical filter or an activated carbon filter
for very high amounts of dissolved iron and manganese.
6. Treat for hardness using a water softener.
7. Neutralize acidity using a neutralizing filter.
8. Remove volatile organic chemicals, trihalomethanes, certain
pesticides and radon using an activated carbon filter.
9. Remove heavy metals, such as lead, mercury, arsenic or
cadmium, with reverse osmosis units or a distiller.
Let's look at several common treatment systems and the
contaminants they are capable of removing to provide safe water.
4
2.3. Disinfecting Water
Drinking water should be free of coliform bacteria. The EPA
drinking water standards indicate that water should contain less
than one coliform organism in 100 milliliters. If your coliform test
was reported as contaminated, take these steps:
1. Disinfect your well
2. Resample the well and have a second coliform test run.
3. If possible, locate and correct the source of bacteria
contamination.
There are a number of ways of disinfecting water but remember,
treatment of a water supply is a safety factor, not a corrective
measure. Don't install a permanent means of disinfection unless
you are sure the contamination originates from the groundwater
and that it is not a temporary condition.
The use of chlorine is the oldest and most common disinfection
method for private water supplies. Chlorine is inexpensive and
readily available, reliable, easy to use and monitor, and effective
against most pathogenic bacteria, virus and cyst organisms. It also
kills non-pathogenic iron, manganese and sulfur bacteria.
Chlorine is also a strong oxidizing agent which causes a problem
mineral such as soluble iron and manganese to change to an
insoluble precipitate so it can be filtered from the water.
For use in the home, chlorine is readily available as sodium
hypochlorite commonly known as household bleach. This product
contains 5 percent available chlorine. Chlorine is also available as
calcium hypochlorite, which is sold in the form of dry pellets. In
this form it has about 70 percent available chlorine.
5
2.4. Emergency Disinfection Measures
During an emergency and to disinfect small quantities of water for
drinking, cooking, and brushing teeth, temporary methods are
sometimes necessary. These methods are not recommended for
general or regular use.
Boiling - First clear the water by letting it settle and filter through
a clean cloth. Boil the water vigorously for one full minute; boiling
will kill all bacteria. Over boiling, however, can concentrate
chemical impurities such as nitrates. Store the boiled water in
sterilized containers if possible. The boiled water will have a "flat"
taste which you can eliminate by aeration.
Chlorine Bleach - Add 10 drops of chlorine bleach to one quart of
water mix the treated water thoroughly and let it stand for 30
minutes. If the water does not have a slight chlorine odor, repeat
the dosage and allow it to stand for another 15 minutes. If the
water tastes too strongly of chlorine, expose it to the air for a few
hours or pour it from one container to another several times.
Granular Calcium Hypochlorite - Add a heaping teaspoon of
calcium hypochlorite to 2 gallons of water. Use one pint of this
chlorine solution in 200 gallons of water.
Chlorine Tablets (Halazone) - Add 1 tablet per quart of water. Be
sure to read the manufacturer's directions carefully.
Iodine Tablets - Add 1 tablet per quart of water - check label for
quantity to use.
6
2.5. Ultraviolet Light Disinfection
Ultraviolet light is a relatively new method of disinfecting private
water systems. Ultraviolet radiation adds nothing to the water and
does not produce any taste or odor. The UV light is produced by a
mercury vapor lamp which produces a disinfecting dose rated in
microwatt-seconds per square centimeter (MWs/cm2). Values of
20,000 MWs/cm2 will kill most types of pathogenic bacteria.
However, viruses are more resistant and variable and may need up
to 45,000 MWs/cm2...
To be effective as a disinfection treatment, ultraviolet radiation
must pass through every particle of water. The thinner the water
film and the slower the water flow, the more effective the system
will be. Also, the water cannot have any turbidity, suspended soil
particles, or organic matter. As a consequence, ultraviolet light
treatment should only be attempted on clear water. A profiler is
recommended on ultraviolet systems as is periodic inspection and
lamp cleaning. As a result, without regular inspection and
maintenance, water treated by UV cannot be guaranteed to be
bacteria free. In fact, one major distributor of the system adds this
disclaimer of liability to its literature: "This product is designed for
use only on water known to be of acceptable bacterial quality. Its
intended use is as a safety device on private and non-municipal
potable supplies already identified as safe to drink. If you think
your water may be unsafe, please contact your local public health
agency."
The cost will be at least $900 for a 47,000 microwatt-second
household UV treatment system with a flow rate of 8 gallons per
minute.
7
2.6. Distillation Disinfection
Distillation provides another water disinfection option as a pointof-use system. Distillers are also used to reduce nitrates, remove
dissolved salts like chlorides, sulfates and carbonates of sodium,
potassium and magnesium, organic matter and other soluble and
suspended materials. Distillation units boil water, making steam
that is condensed and collected as purified water.
Home distillers vary in design. However, the countertop singlebatch version is most common. These distillers cost $250 to
$1,200. All home electric distillers use 100-120 volt a.c. current.
The water output of a home distiller ranges from 3 to 12 gallons
per day. The power consumption of these systems varies from 3 to
5 kilowatt hours of electricity per gallon of distilled water
produced. Thus the electric cost of distilled water can be high.
There are drawbacks to distillation. The most serious is that liquids
with organic molecules whose boiling point is less than that of
water will be carried with vapor into the condensate chamber and
distillate reservoir. Chloroform, phenol and trichloroethylene have
been found in the finished water.
Because distilled water is mineral free, it tends to taste flat and is
hard on metals. Draw water directly from the distiller and not
through any metal piping. Distiller tanks, if not properly used and
maintained, can also become notorious breeders of bacteria
because of the presence of warm water. To remove bacteria and
concentrated salts, disinfect and clean regularly.
8
2.7. Filtration
Filtration represents a broad category of treatment systems used to
remove particles, taste, odor, some organics and minerals, and
some bacteria from the water. Filtration systems fall into several
categories:




Mechanical or Sedimentation Filtration
Oxidation Filtration
Neutralizing Filtration
Reverse Osmosis or Membrane Filtration
In many cases, these filtration systems are an integral component
of other water treatment systems. To remain effective, all filtration
systems must be regularly inspected and maintained.
Mechanical or sedimentation filters simply retain debris as water
passes through the filter unit. Mechanical filters are most effective
for removing particles such as sand, silt, ferric iron, algae and
some bacteria. Their effectiveness will depend on the particle size
and the exit clearance of the filter.
9
2.8. Activated Carbon Filtration
Activated carbon filtration is a common treatment to remove
offensive tastes and odor, color, chlorine and volatile organic
chemicals, pesticides and trihalomethanes (a group of suspected
carcinogens). Activated carbon will not remove bacteria, dissolved
metals such as iron, lead, manganese and copper, or chlorides,
nitrates and fluorides.
Activated carbon filters, usually made up of granulated, powdered
or block carbon, act like a sponge with a large surface area to
absorb contaminants in the water. Activated carbon, made from
coal and nutshells, has a tremendous surface area - as much as 125
acres per pound of carbon. The efficiency of an activated carbon
filter is dependent on the amount of carbon in it and the flow rate
of water through the filter. The typical carbon filter is about 10
inches high and 3 inches in diameter - enough charcoal to treat
about 1,000 gallons of water.
Home-use activated carbon filters are most commonly sold as
faucet-mounted, stationary and line bypass systems. The stationary
system is connected directly to the cold water faucet. The line
bypass system has a separate faucet, but is tapped into the cold
water pipe for its water supply. These systems are typically
installed under the sink and can be purchased for $50 to $375.
Pour-through carbon filters are also on the market. However, due
to the small amount of carbon and minimal water contact time with
the carbon, this system has limited effectiveness. This is also true
of the faucet-mounted carbon filter costing about $25. A carbon
unit for radon removal resembles a water softener tank and costs
about $1,500 plus installation. Without periodic replacement,
carbon filters may provide a breeding ground for bacteria. To
assure maximum effectiveness, replace any carbon filter
frequently, following the manufacturer's recommendations.
10
2.9. Oxidizing Filtration
Oxidizing filters are used mainly to remove iron, manganese and
hydrogen sulfide. Manganese greensand is a common chemically
reactive medium designed to remove iron and manganese that is in
solution. The greensand will also act as a filter and catch iron and
manganese precipitates that have been oxidized. The unit works by
providing oxygen to the iron and manganese from the greensand
bed. As a result, these minerals change from their soluble to
insoluble form. The precipitated minerals become trapped as rust
particles within the greensand filter bed. To remain effective,
manganese greensand filters must be periodically backwashed to
thoroughly remove iron precipitate, and regenerated when the
oxygen is depleted.
2.10. Neutralizing Filtration
Neutralizing filters are typically used for pH modification, or
treating acidic water. A neutralizing filter is normally a pressure
filter tank filled with limestone chips. As the water passes through
the filter bed, calcium carbonate is dissolved into the water and the
water pH is increased, reducing its acidity.
2.11. Reverse Osmosis Filtration
Reverse Osmosis or "R.O." filtration systems for home water
treatment are relatively new, although the process has been used
extensively for industrial processes. Reverse osmosis treatment
decreases dissolved minerals in the water. It successfully treats
water with high salt content, and dissolved minerals such as nitrate,
sulfate, calcium, magnesium, potassium, manganese, aluminum,
fluoride, silica, boron and bicarbonate. R.O. is also effective with
some taste, color and odor-producing chemicals, certain organic
contaminants, and specific pesticides.
11
Some systems treat all the water in the house, while others
primarily improve safety and quality of drinking water. Before
buying water-treatment equipment, have your water supply tested
by a recognized, certified water-testing lab. You need to identify
the type and level of contaminants if you are to get the rightsystem.
Table 1. Typical Water Quall Problems and Recommended
Treatment Systems
Recommended Treatment
Problem
Systems Disinfection
Bacteria and other
Disinfection
microorganisms
Taste and odor
Carbon filter
Oxidizing filter followed by carbon
Hydrogen sulfide gas (rotten
filter; chlorination followed by
egg odor)
sediment filter
Sediment (suspended particles) Fiber filter
Hardness (calcium and
Softener
magnesium)
Softener for up to 5 milligrams per
liter); Iron filter; chlorination
Dissolved iron
followed by sand filter and carbon
filter
Neutralizing filter or chemical-feed
pH (acid or alkaline conditions)
pump
Organic chemicals (pesticides,
Carbon filter
fuel products)
Metals (lead, mercury, arsenic,
cadmium), and other minerals Reverse osmosis unit; distillation
(nitrate, sulfate, sodium)
12
2.12. Fiber Filters
Fiber filters contain spun cellulose or rayon. They remove
suspended sediment (or turbidity). The water pressure forces water
through tightly wrapped fibers around a tubular opening leading to
the faucet. These filters come in a variety of sizes and meshes from
fine to course, with the lower micron rating being the finer. The
finer the filter, the more particles are trapped and the more often
the filter must be changed. Fiber filters may not remove all
contaminants. If taste and odor problems remain, use a carbon
filter after the fiber filter. Fiber filters and replacement cartridges
range in price from a few dollars to several hundred dollars.
Remember, filters do not purify or soften water - they only remove
some suspended particles and dissolved organic compounds that
cause disagreeable odors and tastes.
.
Table 2. Recommended Amounts of Laundry Bleach for Well
Disinfection Height of standing
Height of
4-inch 6-lnch 8-inch 12-inch 24-inch
standing water
well
well
well
well
well
(feet)
50
1 quart 2quarts 1 gallon 2 gallons 8 gallons
2
16
100
2 quarts 1 gallon
4 gallons
gallons
gallons
4
32
200
1 gallon 2 gallons
8 gallons
gallons
gallons
13
2.13. Water Softeners
Hard water is caused by dissolved calcium and magnesium in the
water. Hard water interferes with laundering, washing dishes,
bathing, and personal grooming. It also affects appliances. For
example, scale builds up in water heaters, increasing the costs of
heating water and reducing the life of the appliance.
The calcium and magnesium that cause hardness are reported as
grains per gallon, milligrams per liter (mg/ L), or parts per million
(ppm). Hard water, when used with soap, causes soap deposits that
will not dissolve.
Water is softened by passing through a bed of ion-exchange resin.
The softening process exchanges calcium and magnesium ions in
the water for sodium ions in the resin. About 15 mg of sodium are
added per gallon for each grain of hardness reduced.
When the sodium is used up, the softener needs to be regenerated.
This is done by backwashing to clean the ion-exchange material,
brining with salt (sodium chloride) to replace sodium ions, and
rinsing to remove any excess salt.
A water softener removes small amounts of dissolved iron (5 to 10
ppm). However, if there is oxidized iron or iron bacteria in the
water, the ion exchange resin becomes coated or clogged and loses
its softening ability. In this case, use an iron filter or chlorination to
remove iron.
The size water softener needed depends on the hardness of water,
the quantity to be softened, and the length of time between
recharging. There are three types of ion-exchange softeners for the
home.
14
MANUAL. Each step for recharging the unit must be activated by
hand. Salt is added directly to the single tank of this softener.
SEMI-AUTOMATIC. The homeowner sets the switches when
the system needs recharging. The system completes the process by
itself. A second tank is needed for the brine system.
AUTOMATIC. All steps of the recharging process are controlled
by a timing mechanism that the homeowner sets, based on water
usage. Some models can measure water usage or remaining
softening capacity and recharge themselves only when needed.
Most water softeners have a fully automatic recharging feature.
These softeners also require a second tank for the brine solution.
Water softeners can be installed in various ways. Most people
soften hot and cold water but bypass outside water lines.
The increased sodium in softened water is a concern to people on a
sodium-restricted diet. Therefore, some water softener installations
bypass the cold water line in the kitchen only.
Water softeners can be rented or purchased. Renting a softener or
ion-exchange resin tank is convenient since the user does not
worry about maintenance or regeneration. The dealer regularly
replaces the ion-exchange resin tank, so a second tank for the brine
solution for recharging is not needed.
A water softener can cost $500 to over 41,500, but owning the
equipment could be more economical in the long run than renting
it. The cost of the water softener is balanced against the savings of
soft water. Using soft water reduces the quantity of cleaning
products needed by as much as 500 percent. The home's plumbing
system and water-using appliances will last longer. Other benefits
include the time saved in cleaning and removing scale and better
results in laundry, dish washing, and personal grooming
15
3. INDUSTRIAL WATER TREATMENT
Most industries produce some wet waste although recent trends in
the developed world have been to minimize such production or
recycle such waste within the production process. However, many
industries remain dependent on processes that produce wastewaters
3.1. Treatment of industrial wastewater
The different types of contamination of wastewater require a
variety of strategies to remove the contamination.
3.2. Solids removal
Most solids can be removed using simple sedimentation techniques
with the solids recovered as slurry or sludge. Very fine solids and
solids with densities close to the density of water pose special
problems. In such case filtration or ultrafiltration may be required.
Alternatively, flocculation may be used, using alum salts or the
addition of polyelectrolytes.
3.3. Oils and grease removal
Many oils can be recovered from open water surfaces by skimming
devices. However, hydraulic oils and the majority of oils that have
degraded to any extent will also have a soluble or emulsified
component that will require further treatment to eliminate.
16
Dissolving or emulsifying oil using surfactants or solvents usually
exacerbates the problem rather than solving it, producing
wastewater that is more difficult to treat.
The wastewaters from large-scale industries such as oil refineries,
petrochemical plants, chemical plants, and natural gas processing
plants commonly contain gross amounts of oil and suspended
solids. Those industries use a device known as an API oil-water
separator which is designed to separate the oil and suspended
solids from their wastewater effluents. The name is derived from
the fact that such separators are designed according to standards
published by the American Petroleum Institute (API).
The API separator is a gravity separation device designed by using
Stokes Law to define the rise velocity of oil droplets based on their
density and size. The design is based on the specific gravity
difference between the oil and the wastewater because that
difference is much smaller than the specific gravity difference
between the suspended solids and water. The suspended solids
settles to the bottom of the separator as a sediment layer, the oil
rises to top of the separator and the cleansed wastewater is the
middle layer between the oil layer and the solids. Typically, the oil
layer is skimmed off and subsequently re-processed or disposed of,
and the bottom sediment layer is removed by a chain and flight
scraper (or similar device) and a sludge pump. The water layer is
sent to further treatment consisting usually of a dissolved air
flotation (DAF) unit for additional removal of any residual oil and
then to some type of biological treatment unit for removal of
undesirable dissolved chemical compounds.
17
API(Fig.1)
Parallel plate separators are similar to API separators but they
include tilted parallel plate assemblies (also known as parallel
packs). The parallel plates provide more surfaces for suspended oil
droplets to coalesce into larger globules. Such separators still
depend upon the specific gravity between the suspended oil and the
water. However, the parallel plates enhance the degree of oil-water
separation. The result is that a parallel plate separator requires
significantly less space than a conventional API separator to
achieve the same degree of separation.
18
Typical parallel plate separator (fig 2)
3.4. Removal of biodegradable organics
Biodegradable organic material of plant or animal origin is usually
possible to treat using extended conventional wastewater treatment
processes such as activated sludge or trickling filter. Problems can
arise if the wastewater is excessively diluted with washing water or
is highly concentrated such as neat blood or milk. The presence of
cleaning agents, disinfectants, pesticides, or antibiotics can have
detrimental impacts on treatment processes.
Fig.3
19
3.5. Activated sludge process
Activated sludge is a biochemical process for treating sewage and
industrial wastewater that uses air (or oxygen) and microorganisms
to biologically oxidize organic pollutants, producing a waste
sludge (or floc) containing the oxidized material. In general, an
activated sludge process includes:


An aeration tank where air (or oxygen) is injected and
thoroughly mixed into the wastewater.
A settling tank (usually referred to as a "clarifier" or "settler")
to allow the waste sludge to settle. Part of the waste sludge is
recycled to the aeration tank and the remaining waste sludge
is removed for further treatment and ultimate disposal.
3.6. Trickling filter process
A trickling filter consists of a bed of rocks, gravel, slag, peat
moss, or plastic media over which wastewater flows downward
and contacts a layer (or film) of microbial slime covering the bed
media. Aerobic conditions are maintained by forced air flowing
through the bed or by natural convection of air. The process
involves adsorption of organic compounds in the wastewater by
the microbial slime layer, diffusion of air into the slime layer to
provide the oxygen required for the biochemical oxidation of the
organic compounds. The end products include carbon dioxide gas,
water and other products of the oxidation. As the slime layer
thickens, it becomes difficult for the air to penetrate the layer and
an inner anaerobic layer is formed.
The components of a complete trickling filter system are:
fundamental components:
20




A bed of filter medium upon which a layer of microbial slime
is promoted and developed.
An enclosure or a container which houses the bed of filter
medium.
A system for distributing the flow of wastewater over the
filter medium.
A system for removing and disposing of any sludge from the
treated effluent.
The treatment of sewage or other wastewater with trickling filters
is among the oldest and most well characterized treatment
technologies.
A trickling filter is also often called a trickle filter, trickling
biofilter, biofilter, biological filter or
biological trickling filter.
Fig .4 (Trickling filter)
Fig .5
A schematic cross-section of the contact face of the bed media in a
trickling filter
a typical complete
trickling filter system
21
3.7. Treatment of other organics
Synthetic organic materials including solvents, paints,
pharmaceuticals, pesticides, coking products and so forth can be
very difficult to treat. Treatment methods are often specific to the
material being treated. Methods include Advanced Oxidation
Processing, distillation, adsorption, vitrification, incineration,
chemical immobilisation or landfill disposal. Some materials such
as some detergents may be capable of biological degradation and
in such cases; a modified form of wastewater treatment can be
used.
3.8. Treatment of acids and alkalis
Acids and alkalis can usually be neutralized under controlled
conditions. Neutralization frequently produces a precipitate that
will require treatment as a solid residue that may also be toxic. In
some cases, gasses may be evolved requiring treatment for the gas
stream. Some other forms of treatment are usually required
following neutralization.
Waste streams rich in hardness ions as from de-ionization
processes can readily lose the hardness ions in a buildup of
precipitated calcium and magnesium salts. This precipitation
process can cause severe furring of pipes and can, in extreme
cases, because the blockage of disposal pipes. A 1 meter diameter
industrial marine discharge pipe serving a major chemicals
complex was blocked by such salts in the 1970s. Treatment is by
concentration of de-ionisation waste waters and disposal to landfill
or by careful pH management of the released wastewater.
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3.9. Treatment of toxic materials
Toxic materials including many organic materials, metals (such as
zinc, silver, cadmium, thallium, etc.) acids, alkalis, non-metallic
elements (such as arsenic or selenium) are generally resistant to
biological processes unless very dilute. Metals can often be
precipitated out by changing the pH or by treatment with other
chemicals. Many, however, are resistant to treatment or mitigation
and may require concentration followed by landfilling or recycling.
Dissolved organics can be incinerated within the wastewater by
Advanced Oxidation Processes.
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References:
1. ^ European Environment Agency. Copenhagen,
Denmark. "Indicator: Biochemical oxygen demand in
rivers (2001)."
2. ^ a b Tchobanoglous, G., Burton, F.L., and Stensel, H.D.
(2003). Wastewater Engineering (Treatment Disposal
Reuse) / Metcalf & Eddy, Inc. (4th ed.). McGraw-Hill
Book Company. ISBN 0-07-041878-0.
3. ^ a b c d Beychok, Milton R. (1967). Aqueous Wastes from
Petroleum and Petrochemical Plants (1st ed.). John Wiley
& Sons. LCCN 67019834.
4. ^ American Petroleum Institute (API) (February 1990).
Management of Water Discharges: Design and Operations
of Oil-Water Separators (1st ed.). American Petroleum
Institute.
5. ^ a b Beychok, Milton R. (December 1971). "Wastewater
treatment". Hydrocarbon Processing: 109–112. ISSN
0818-8190.
6. http://en.wikipedia.org/wiki/Water_treatment( cited in 19
June 2009 )
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