Q.20. What are ‘Solid Wastes’. Discuss their
types, effects and name the various methods used to dispose solid wastes.
Explain any one of them with its merits and demerits. (AKTU. - 2005-06)
Related Questions
-
Q. Write short waste management. (AKTU. - 2010 - 11)
Q. What is solid wasted? Discuss in
brief the various ways of solid waste disposal methods. (AKTU. - 2008-09, 11 - 12, 12 -
13)
Q. What are the sources and effects of
solid waste? Explain waste minimization technique. (AKTU. - 2010 -11)
Ans. Solid Waste: -
Human and animal activities generate many
wastes that are discarded as useless or unwanted. These wastes are normally
solid and result in landscape pollution. The term ‘refuse’ is often used
interchangeably with the term ‘solid-wastes. The term solid wastes encompasses
the highly heterogenous mass of discarded materials or throwaways from the
urban community (i.e. residential and commercial activities) as well as the
more homogenous accumulation of wastes generated by agricultural and industrial
activities.
Types:
-
There are three general
categories of solid-wastes:
(i)
Municipal Wastes: -
Municipal wastes are those wastes which
arise from household activities, restaurants, public places, institutions,
markets, street-sweepings etc. and typically include garbage, rubbish, ashes
(due to burning of coal, wood etc.) demolition and construction wastes,
street-sweepings, dead animals, etc. and also treatment plant waste.
(ii)
Industrial Wastes: -
Industrial wastes are those wastes which
arises from industrial activities, and typically include rubbish, ashes,
construction and demolition wastes, special wastes and toxic wastes.
(iii)
Hazardous Waste: -
Are those wastes that pose a substantial
danger immediately or over a period of time to human, plant or animal life? A
waste is said to be hazardous if it exhibits any of the following
characteristics, viz ignitability, corrosivity, reactivity or toxicity. Typical
hazardous wastes are radioactive substances, chemical, biological wastes,
flammable wastes and explosives. The sources of hazardous wastes are
industries, nuclear plants, hospitals, research institutes, laboratories, etc.
Effects:
-
The improper handling and transfer of the
solid wastes results in various health and environmental hazards, such as:
1. Diseases like bacillary
dysentery, diarrhoea and amoebic dysentery may result in humans from food and
water contamination through files, which breed on the refuse dump and solid waste.
2. Rats depending upon these
solid wastes may also cause plague, salmonellosis, trichinosis, endemic typhus
like diseases through direct bite.
3. The crops and water supply
may also get contaminated and may result in large scale epidemic of cholera,
jaundice, gastrointestinal diseases, hepatits etc.
4. Solid wastes may also chock
the drains and gully pits resulting in water logging, which in turn results in
the breeding of mosquitoes and thus danger of malaria and dengue.
5. Percolation of decomposed
garbage dumps into soil may result into pollution of underground water and
land.
Methods
of Solid-wastes Disposal: -
Various
Methods for the Disposal of Solid Wastes: -
The various methods of
solid-wastes disposal are:
(i) Land
filling (ii) Incineration (iii)
Pulverization (iv) Composting (v)
Pyrolysis and (vi) Disposal into sea.
(i)
Disposal of Solid-Wastes by Land Filling: -
In this method, solid wastes are
carried and dumped into the low lying areas. The refuse is filled up or dumped
in layers of 1.5 m or so and each layer is covered by good earth of at least 20
cm thickness, so that refuse is not directly exposed. Each layer is left out
for at least seven days and compaction by trucks is carried out for its
settlement, before starting filling the next layer. Insecticides like DDT
should be sprayed on top to prevent breeding of mosquitoes and files.
Advantages:
-
1. Simple and economical.
2. No costly plant and equipment is required.
3. Skilled labour is not required.
4. Separation of different kinds of solid
wastes is not required.
5. No residue or by product; hence no further
disposal.
6. Low-lying areas can be reclaimed and put to
better use.
Disadvantages:
-
1. Large land area requirement.
2. Continuous revolution of foul smell near the
site of disposal.
3. Use of insecticides is required.
4. Covering good earth required for top layer
may sometimes be difficult to obtain.
5. The biggest disadvantage is formation of
‘leachate’. It is a coloured liquid formed due to seepage of rainy water into
the land fill. This water may dissolve the harmful and carcinogenic compounds
present in the refuse. When such a polluted water contaminates the ground
water, it may lead to diseases like Cholera, Typhoid, Polio etc.
(ii)
Incineration: -
Incineration means burning of
the solid-wastes in properly constructed hearth of furnaces. This method is
generally used when suitable dumping land areas are not available and disposal
in sea is not possible. When solid-waste is collected together, it is better to
separate the non-combustible and inert material like earth, broken glass,
chinaware, metals etc. So as to reduced the load on the hearth. The combustible
garbage rubbish and dead animals are only burnt.
The final products will be ashes
and clinkers. The ashes are dispersed by dumping in low lying areas, while the
clinkers can be used as aggregate for low grade concrete or as road material.
Advantages:
-
1. The method is sanitary, as all the pathogens
and insects are destroyed.
2. No odour and dust nuisance.
3. Same revenue can be generated by raising
steam power and selling of the clinkers.
Disadvantages:
-
1. Relatively high initial cost.
2. Nuisance of smoke, odour and ash during the
improper functioning of incinerators.
(iii)
Pulverization: -
In this method , the solid waste
is pulverized in grinding machines so as to reduce its volume and change its
physical character. By doing so it becomes practically odourless and
unattractive to insects. The method is quite costly, and hence not commonly
used, particularly in India.
(iv)
Composting: -
Bacterial decomposition of the
organic compounds of the municipal solid waste result in formation of humus or
compost and the process is known as composting. It is a hygenic method which
converts the solid-wastes into manure through anaerobic bacterial action. This
method is best suited to Indian conditions, especially for small and medium
size towns; Since it solves three problems simultaneously-disposal of
solid-wastes, disposal night soil (where there is no water carriage system of
sanitation), and production of valuable manure for crops.
(v)
Pyrolysis: -
In pyrolysis, the chemical constituents
and chemical energy of some organic wastes is recovered by destructive
distillation of the solid waste. In pyrolysis, the combustible constituents of
the solid-waste are heated in a specially designed retort like chamber, known
as pyrolysis reactor at 650 to 10000C in an oxygen free (or low oxygen)
environment. Its merits and demerits are same as that of incineration process
discuss earlier.
(vi)
Disposal into sea: -
This method of solid-waste disposal can be
used in coastal areas having deep sea water (> 30 m) at a reasonable
distance (< 16 to 20 km), and with strong forward currents. This is quite a
simple and cheap method, but it has following disadvantages:
1. The bulky and lighter components of
solid-wastes float, spread, and tend to return to the shores during high tides.
2. During monsoons or stromy weather,
solid-waste has to be either stored or disposed of by some other methods.
3. Some portion of the solid-wastes may return
and spoil the beaches, despite all the necessary precautions.
