1. Waste Treatment
Books Ref:
1. Environmental Chemistry, A.K. DE
2. Fundamentals of Environmental Chemistry, S.
E. Manahan, Lewis Publisher, NY
3. Environmental Chemistry, Ajay Kumar Bhagi
and G.R.Chatwal
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Course No-424
7th
Chapter
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2. Definition of Wastes
Human society produces some unwanted and discarded
materials which are called wastes.
Wastes are produced from different activities such as
household activities, agricultural activities industrial activities,
hospitals, educational institutions, mining operations, and so
on.
These sources generate different types of wastes, many of
which are hazardous in nature. They cause spread of many
diseases.
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3. Definition of Wastes
In general, the wastes maybe categorized as follows:
Solid wastes:
The solid wastes are the useless and unwanted substances
discarded by human society. These include urban wastes,
industrial wastes, agricultural wastes, biomedical wastes and
radioactive wastes. The term refuse is also used for solid waste.
Liquid wastes:
Wastes generated from washing, flushing or manufacturing
processes of industries are called liquid wastes. Such a waste is
called sewage. The most common practice is to discharge it on
the ground, nallahs, rivers and other water bodies, often without
any treatment.
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4. Definition of Wastes
Gaseous wastes:
These wastes are released in the form of gases from
automobiles, factories, burning of fossil fuels etc. and get
mixed in the atmosphere. These gases include carbon
monoxide, CO2, sulphur dioxide, nitrogen dioxide, ozone,
methane, etc.
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5. Sources of Wastes
Wastes produced are classified as follows:
1. Urban or Municipal wastes
2. Industrial wastes
3. Commercial wastes
4. Agricultural wastes
Municipal Solid Waste:
The wastes, collected from the residential houses, markets,
streets and other places mostly in the urban areas and
disposed of by municipal bodies are called municipal solid
wastes (MSW).
In general, the urban solid wastes are called refuse. The
Municipal solid wastes are a mixture of paper, plastic, clothes,
metals, glass, organic matter etc. generated from households,
commercial establishments and markets.
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7. Sources of Wastes
Industrial Wastes:
Industrial wastes are released from chemical plants, paint
industries, cement factories, power plants, metallurgical plants,
mining operations, textile industries, food processing industries
petroleum industries and thermal power plants. These
industries produce different types of waste products. Industrial
solid wastes can be classified into two groups.
1) Non-hazardous wastes:
These wastes are produced from food processing plants, cotton
mills, paper mills, sugar mills and textile industries.
2) Hazardous wastes:
Hazardous wastes are generated by nearly every industry.
Metals, chemical, drugs, lather, pulp, electroplating, dye, rubber
are some of important examples. Liquid Industrial waste that
runs into a stream from a factory can kill the aquatic fauna and
also cause health problems for humans. 7
9. Sources of Wastes
Agricultural Wastes:
Agricultural areas produce plants and animals wastes.
Excess use of fertilizer, pesticides and other chemicals used in
agriculture and the wastes formed from these cause land and
water pollution. They also contaminate the soil.
Among pesticides chlorinated hydrocarbons, DDT, endrin, dieldrin,
lindane, parathion, malathion and endosulphon are important
which are absorbed by the soil and contaminate crops grown in
the soil.
Other agriculture wastes are produced from sugar factories,
tobacco processing units, slaughter houses, livestock, poultry
etc.
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10. Sources of Wastes
Commercial Wastes:
With the advancement of modem cities, industries and
automobiles, huge amount of wastes are generated daily.
These include markets, roads, buildings, hotels, commercial
complexes, hostels, auto workshops, printing press etc.
Hospitals, nursing homes and medical institutes also release
tremendous amount of wastes which are hazardous and are
much toxic in nature.
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11. Classification of Wastes
Biodegradable Wastes:
These wastes are natural organic compounds which are
degraded or decomposed by biological or microbial action.
Biodegradable wastes are generated in food processing units,
cotton mills, paper mills, sugar mills, textile factories and
sewage.
Waste of slaughterhouses is biodegradable and some part of it
is used, for example, skin is used to make shoes.
Most of the wastes from these industries are reused. When
these wastes are in excess they act as pollutants and are not
easily decomposed and they take much time for their
decomposition.
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12. Classification of Wastes
Non-Biodegradable Wastes:
These are not decomposed by microbes but are oxidized and
dissociated automatically.
Coal stone, metal scraps, sludge are generated from colliery
operations.
Refineries produce inert dry solids and varieties of sludge
containing oil. Fly ash is the major solid waste from thermal
power plants.
Generally, these wastes are not reused and accumulate in the
ecosystem and some of it move through biogeochemical
cycles.
Non-biodegradable wastes also include lead, plastics, mercuric
salts etc.
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13. Classification of Wastes
Hazardous wastes:
Many chemical, biological, explosive or radioactive wastes,
which are highly reactive and toxic, pose a severe danger to
human, plants or animal life and are called hazardous wastes.
They are highly toxic in nature. Hazardous wastes, when
improperly handled, can cause substantial harm to human
health and to the environment.
Hazardous wastes may be in the form of solids, liquids, sludge’s
or gases.
They are generated primarily by chemical production,
manufacturing and other industrial activities.
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14. Classification of Wastes
Hazardous wastes:
The important hazardous wastes are lead, mercury, cadmium,
chromium, many drugs leather, pesticides, dye, rubber and
effluents from different industries.
They may cause danger during inadequate storage,
transportation, treatment or disposal operations.
The hazardous waste materials may be toxic, reactive, ignitable,
explosive, corrosive, infectious or radioactive.
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15. Waste treatment or management
Sanitary Landfill:
Miscellaneous refuse materials are those from household,
hotels, stores, markets, restaurants etc. (e.g. food wastes,
vegetables and animal wastes, paper, cardboard, wood,
boxes, rubber, leather, plastics, tin cans, crockery glass,
metals etc.) ashes (from fires used for cooking, heating,
buildings etc.), dead animals, industries and agricultural fields,
etc.
A method of disposing of solid waste on land without creating
nuisances or hazards to public health or safety, by utilizing
the principles of engineering to confine the solid waste to the
smallest practical area, to reduce it to the smallest practical
volume, and to cover it with a layer of earth at the conclusion
of each day's operation or at more frequent intervals as may
be necessary.
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16. Waste treatment or management
Sanitary Landfill:
Most of the solid waste is dumped on land in heaps in
uncontrolled manner in developing countries.
Some waste is used for land filling in abandoned quarries or
mines.
For sanitary landfill, the following principles should be followed;
✔ Solid wastes should be deposited in a regulated manner.
✔ Solid wastes should be spread in thin layers with ground
cover of at least 15 cm.
✔ All factors likely to contribute to water pollution should be
eliminated.
✔ The waste should not be burnt openly.
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18. Waste treatment or management
Composting:
This is the biological process where fresh organic wastes are
allowed to be decomposed into humus-like substances.
The process is conducted by a complete automatic system
which consists of several steps:
The crude refuse is dumped into a container or a belt conveyor.
Iron or metallic particles are removed by a magnetic separator.
The material is then transferred in a wet condition to a rotatory
cylinder.
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19. Waste treatment or management
Composting:
Control humidity – Ventilation and agitation systems of
composter help carry away excess moisture produced from
the digestion and hence avoid drowning the micro-organisms.
The cylinder rotates slowly on large tyres and the wastes move
from one end to the other. They are thoroughly mixed and
pulverized by abrasion.
Air is continuously drawn into the composters to provide
sufficient oxygen for the micro-organisms. Periodical turning
or stirring of the waste can enhance the exposure of the micro-
organisms to the air.
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20. Waste treatment or management
Composting:
Maintain suitable temperature – Temperature control device
together with the agitator ensure an optimum thermal zone
for the digestion process.
Here aerobic micro-organisms ensure rapid decomposition of
the wastes under aerobic conditions.
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22. Waste treatment or management
Incineration:
This is the preferred technique for waste management,
particularly in the developed countries.
It reduces the waste volume by 90 percent at 9000
– 10000
C.
Incineration offers environmental friendly technique – free from
corrosion, emission of offensive odours and also free from
bacteria and wet organic matter which gives off foul orders
and gases.
The waste heat from incineration can be utilized for
supplementing electricity generation for domestic heating etc.
The only drawbacks is that the technique is costly at present
requiring expensive equipment.
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23. Waste treatment or management
Incineration:
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Waste
Feed
Flue
Gas Out
Burner
Combustion
Air Inlet
Grate
Ash
Door
24. Physical Method of Hazardous Waste Treatment
Physical waste treatment may occur at three major levels-
primary, secondary and polishing.
Primary treatment is usually preparation for further treatment,
although it can result in the removal of by-products and
reduction of the quantity and hazard of the waste.
Secondary treatment detoxifies, destroys and removes
hazardous constituents.
Polishing usually refers to treatment of water removed from
wastes before discharge. The term may also apply to the
treatment of other products so that they may be safely
discharged or recycled.
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26. Recycling
Recycling is the process of converting waste materials into new
materials. It is an alternative to "conventional" waste disposal,
can save material and help lower greenhouse gas emissions.
Wherever possible, recycling and reuse should be accomplished
on-site because it avoids having to move wastes, and
because a process that produces recyclable materials is often
the most likely to have use for them.
The four broad areas in which something of value may be
obtained from wastes are the following:
✔ Direct recycle as raw material to the generator, as with the
return to feedstock of raw materials not completely consumed
in a synthesis process
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27. Recycling
✔ Transfer as a raw materials to another process; a substance
that is a waste product from one process may serve as a raw
material for another sometimes in an entirely different industry
✔ Utilization for pollution control or waste treatment, such as
use of waste alkali to neutralize waste acid
✔ Recovery of energy, for example, from the incineration of
combustible hazardous wastes
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28. Examples of Recycling
✔ Ferrous metals composed primarily of iron and used largely as
feedstock for electric-arc furnaces.
✔ Nonferrous metals, including aluminum, copper and copper alloys,
zinc, lead, cadmium, tin, silver and mercury.
✔ Metal compounds, such as metal salts
✔ Inorganic substances, including alkaline compounds, acids and
salts
✔ Glass, which makes up about 10% of municipal refuse
✔ Paper, commonly recycled from municipal refuse
✔ Plastic, consisting of a variety of moldable polymeric materials and
composing a major constituent of municipal wastes
✔ Rubber
✔ Organic substances, especially solvents and oils, such as
hydraulic and lubricating oils
✔ Catalysts from chemical synthesis or petroleum processing
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