The waste may be defined as material for which no use or reuse is intended. The wastes generated from the natural Processes and anthropogenic activities which pollute the environment and make the earth an unhealthy planet, is termed as environmental wastes, depending upon the physical states of wastes, these are of three types:
(1) Solid waste,
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(2) Liquid waste
(3) Gaseous waste.
The accumulation of wastes in different forms causes serious environmental hazards. So it’s high time for the present society to take appropriate steps for the management of waste, possibly through its recycling. The management of waste is another way of conservation of resources.
1. Management of Solid Waste:
Solid wastes include solid portions of the discarded material such as glass bottles, crockeries, plastic containers, metals and radioactive wastes. The solid wastes may be biodegradable or non-biodegradable. The biodegradable solid wastes are agricultural wastes, food wastes, paper, food processing by products, manure, yard wastes etc. The non-biodegradable wastes include plastics, metals, synthetic materials, polythene, radioactive wastes etc.
The solid waste management involves disposal of solid waste to land (or ocean) or recovering and reproducing useful substances from the waste through recycling.
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The entire methodology of solid waste management is based on:
(A) Collection of Waste,
(B) Disposal,
(C) Resource recovery.
(A) Collection of Waste:
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The solid wastes are usually collected by a covered truck.
(B) Disposal of Waste:
After the collection of wastes, the wastes are disposed of by any one of the methods described below
(i) Dumping:
It is a process of controlled and final disposal of waste at land fill sties which must be done using state of the art methods, {base sealing, treatment of percolated water, landfill gas disposal/utilisation etc.)
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(ii) Sanitary land fill:
It is a method of disposing of the waste without creating nuisances or hazards to public health by using the principles of engineering. In the process, the waste is confined to smallest practical volume by covering it with a layer of earth, at the conclusion of each day’s operation.
(iii) Incineration:
It is a method of converting the volume of waste to ashes by burning. This method is adopted when the cost of land filling is very high.
(iv) Pyrolysis:
It is a method of burning waste in absence of oxygen or air. The process reduces volume of the waste and produces stable end products.
(v) Composting:
This process involves preparation of refuse and degrading the organic matter in waste in to bio-fertilizer by aerobic micro-organisms. After about 3 to 4 weeks of the operation, the composting product becomes ready for curing, blending with additives, bagging and marketing.
(vi) Biogas technology:
The organic matter present in solid waste is decomposed by putrefactive bacteria in absence of air (anaerobic condition) to biogases in a biogas digestor. The approximate composition of biogas is 60% methane (CH4) and 40% C02 For better yield of biogas, the organic solid waste may be mixed with poultry waste, grass, leaves, straw, kitchen waste etc.
(C) Resource recovery (Recycling):
By the process of recycling a number of useful products can be obtained from the solid wastes.
Some important products obtainable from solid wastes are described below:
1. Electricity can be generated from incinerated plastics.
2. Synthetic oil can be produced from plastic wastes.
3. Waste papers and cardboards from sugar cane bagasse can be used for the preparation of unbreakable dolls, packing cardboards etc.
4. Metals can be recycled from the industrial scrap.
5. Ethyl alcohol can be produced from agricultural wastes.
6. Heavy metals can be extracted by bioleaching technology.
7. Waste glasses can be used for the preparation of new glass bottle.
8. Bricks and concretes can be prepared by using ash generated by power plants, slit from water works and red mud from aluminum industry.
Some industrial wastes and their subsequent uses are shown in Table 11.1.
2. Management of Liquid Wastes:
Liquid wastes are the liquid part of the waste material. Liquid waste includes effluents of industries, fertiliser and pesticide solutions from agricultural fields, leachate from landfills, urban runoff of untreated waste water and garbage, mining wastes etc. The liquid waste may contain nontoxic inorganic substances or toxic organic substances.
Some important liquid waste management methods are described below:
1. Sewage treatment:
The process of sewage treatment involves the following methodology:
(a) Dilution:
In this method, the sewage is subjected to perfect dilution so that the dissolved oxygen in natural water decomposes the organic wastes completely, thereby reducing the turbidity. The reduction of turbidity favours easier penetration of sun light and natural ecosystem is restored.
(b) Mechanical treatments:
The sewage is allowed to pass through different screens, filters, grit chambers, sedimentation basins etc. At first the sewage is filtered to remove suspended Particles. Then the sewage is subjected to grinding followed by some chemical treatment.
By this operation, the minute solid Particles present within the sewage get coagulated and settle at the bottom. The precipitates are separated either by filtration or by gravity settling. The sediments obtained above are then put in sludge digester where it is digested in absence of air to release biogas.
(c) Biological treatments:
In this method, the sewage is passed through trickling filters where aerobic bacteria degrade the sewages as it seeps through large vat beds filled with crossed stones covered with bacterial growth. Alternatively, the sewage is pumped into a large tank, mixed with bacteria rich sludge and agitated heavily in presence of sufficient amount of oxygen for several hours which causes bacterial degradation of organic waste.
The waste is then pumped into sedimentation tank where the suspended solids settle as sludge. The entire solution is filtered to separate sludge and effluent. The sludge is taken in an anaerobic digester and broken down. After suitable treatment, the sludge can be used as fetiliser. The effluent may be chlorinated to kill the pathogenic microbes and discharged in to water -bodies.
(d) Chemical treatments:
The sewage obtained after mechanical or biological treatments is subjected to specific chemical treatment followed by some physical operation:
(i) Precipitation:
The sewage may be treated with calcium oxide to precipitate up to 90% of phosphates and suspended particles. The precipitate separates and settles at the bottom.
(ii) Adsorption:
The effluent is treated with activated charcoal which adsorbs colour, odour and dissolved organic compounds.
(iii) Osmosis:
The dissolved organic and inorganic substances can also be separated by the process of osmosis.
(iv) Chemical oxidation:
The effluent may be subjected to oxidation in presence of ozone or hydrogen peroxide to remove dissolved organic compounds.
(v) Removal of ammonia:
After the first operation, the waste water is introduced into a metal tower from which it trickles down over a series of plastic baffles plates and air is forced upwards which removes ammonia gas.
2. Removal of ammonia:
The treatment of industrial effluents in ‘Effluent Treatment involves chemical or primary treatment (by methods of neutralization, sedimentation, coagulation, precipitation etc.) followed by biological or secondary treatment (by activated sludge and trickling filter method) and tertiary treatment (by methods of ion exchange, reverse osmosis, chemical oxidation).
3. Effluent water can be used to grow algae and aquatic plants to produce biomass for biogas plants.
4. The effluents containing heavy metals like cadmium, mercury, lead etc. can be purified by growing water hyacinth plants.
5. The sewage with organic nutrients is stored in specially constructed shallow ponds called as oxidising or stabilizing pond. In the pond, green algae and bacteria grow in presence of sun light, consuming organic nutrients. This water contains enough nitrogen, phosphorous and potassium and is highly helpful for the growth of plants.
3. Management of Gaseous Wastes:
The gaseous wastes are generated in to environment mainly due to anthropogenic activities. The gaseous wastes include carbon dioxide (CO2), methane (CH4), chlorofluorocarbon (CFC), oxides of nitrogen (NOx), carbon monoxide (CO), oxides of sulphur (SOx) etc. These gaseous wastes can cause serious environmental hazards. Therefore, it is highly essential to take appropriate steps for the proper management and control of gaseous wastes in the environment.
Some important control measures are described below:
(i) The gaseous pollutant like SO2, H2S, HC1, Cl2, NH3, ec. can be removed by absorption in (using appropriate liquid) wet scrubbers.
(ii) The use of smokeless chulhas, solar cookers and biogas can reduce the production of smoke.
(iii) The industries should use precipitators, scrubbers and filters to check production of particulate matter.
(iv) The emission of hydrocarbons from vehicles can be checked by the use of unleaded petrol.
(v) There should be large scale of plantation which will reduce CO2 level and increase O2 level of atmosphere.
(vi) There should be large chimneys in industries.
(vii) The automobile emission can be controlled by:
(a) Control of exhaust emission,
(b) Control of evaporation emission,
(c) Control of crank case emission,
(d) Using engine alternative to gasoline engine,
(e) Use of CNG instead of diesel.
(viii) Air cleaning devices like gravity settlers, cyclone separators, wet collectors, electrostatic precipitators etc. should be used for the cleaning of air before their discharge into atmosphere.
(ix) Public awareness should be created regarding hazards of air pollutant accumulation in environment.
(x) Adequate legislation (Air act) should compel to control air pollution. Severe punishment should be specified for the defaulters.