Most common method of disposing of wastes is to dump them in low-lying areas on the outskirts of towns which is very haphazard and unscientific. This has serious environmental impacts like water pollution, methane emissions, and soil degradation. The average density of Indian municipal waste at the point of collection varies from 400 to 600 kg per cubic metre. At the landfill site, however, the density is much higher because of compaction and putrefaction.
Compactors were introduced in India in the late 1970s by a few large corporations to make the transportation of waste more efficient. The waste is compacted with a hydraulic press fitted within a truck or at the landfill site. If the waste is not compacted, it putrefies with time. The density of dumped refuse can increase two folds in about six months due to putrefaction and self-compaction of biodegradable organic matter. It has been observed that soil can be contaminated with soluble salts and metals from solid wastes which may cause dispersion of soil particles, thus adversely affecting soil structure.
On the other hand, the compostable part of municipal solid waste if separated can be a good source of manure. As traditional disposal sites do not have an impermeable lining, contamination to surface water and groundwater is by far the most serious environmental impact. Surface run-off and leachate from dump-sites can easily contaminate natural sources of water. The composition of leachate depends on many factors such as the composition of waste, elapsed time, temperature, moisture, available oxygen, and management practices. Leachate characteristics at disposal sites reveal that values of TDS (total dissolved solids), chloride, TOC (total organic carbon), and COD (chemical oxygen demand) are always more for pit leachates than for extractable pollutants from degradable solid waste.
However, there is a lot of variation in toxic heavy metals in pit leachate and in extractable pollutants, indicating that degraded solid waste generates very strong leachate containing high organic and inorganic pollutants and may contaminate the water bodies. Once contaminated, the cost of treating groundwater and surface water is prohibitive. And the cost, in terms of ill health and the subsequent loss in productivity are even higher.
The other source of air pollution is due to decomposition of the biodegradable component in landfills. Waste in landfills is initially degraded aerobically, using up oxygen and converting the organic matter to carbon dioxide. After sometime further degradation is anaerobic, during which methanogenic bacteria generate methane. Landfill gas typically contains 40% to 60% methane by volume and carbon dioxide. Methane can be an environmental hazard by migrating from landfills either laterally or upward into the atmosphere. At low concentration, it can damage vegetation and cause unpleasant odors but at higher concentrations it forms explosive mixtures. The role of methane in global atmospheric changes has received increasing attention recently. Methane from landfills contributes significantly to annual global emissions of methane. Although actual emission is estimated with a great deal of uncertainty, yet methane has a global warming potential up to 63 times to that of carbon dioxide (depending on the time horizon) and accounts for about 15% of the global warming due to anthropogenic emissions
A large proportion of recyclable components, i.e., paper, plastics, metal, etc. is collected by rag pickers from the garbage bins, from roadside, or in streets, market places, etc. in metropolitan cities, thus supplying raw material to the flourishing recycling units. About 0.75 million tones of plastics wastes are recycled every year in India. In metro cities , this business is very lucrative and can fetch anything between Rs 3 to Rs 15 per kg at each stage of the transfer. In smaller cities and towns, about 14%-20% of the total garbage consists of recyclable items (TERI, 1998). This excludes the plastics and paper retained in the households to be sold. The plastics recycling industry in India is valued at 25 billion rupees at the pre-granulation stage and 39 billion rupees at the post-granulation stage.
The landfill gas can be used as substitute of fossil fuels, generating additional revenue and reducing pollution. Lately, conversion of landfill gas into powder has become a lucrative business in the developed world. Composting the organic portion of municipal solid waste can produce 0.6 million tones of organic fertilizer every year, which could partially offset the degradation of land and pollution due to indiscriminate application of chemical fertilizers.
Due to foul odors emanating from landfills and explosion hazards due to emissions of methane, a 1- to 2- km-wide strip around the site is unsuitable either for habitation or for plant life. As a result, the land is left unused, despite acute scarcity of land in cities and the soaring land prices.
IMPACTS ON HUMAN HEALTH
The poor waste management is associated with increased health problems ranging from epidemics of vector-borne or food/borne diseases to the adverse effects due to contamination of groundwater. The effects of such health hazards are difficult to quantify because of limited epidemiological studies. The health hazards can be categorized as follows:
• Direct contact with waste in the case of rag pickers who separate recyclable material from the waste.
• Direct contact with waste in the case of workers involved in waste disposal.
• Indirect effects because of contamination of soil, air, and water as a result of poor management of landfill sites.
The municipal workers handle wastes mostly without protective devices like gloves or waterproof boots. The workers can be infected at all stages, from collecting the waste at source to handling it at landfill sites. The pathogens can enter either through skin and mucous membranes or along with inhaled air. Flies are the most visible indicator of unsanitary conditions. If the garbage contains night-soil, pathogens like enteropathogens, Shigella, Salmonella, and Entamoeba adhere to the feet of these flies. The flies then alight on food kept in the open and thus transmit the pathogens to those who eat the contaminated food.
As far as the management aspects of wastes are concerned, the following possibilities are of significance to us:
1. Reduction in raw material use
2. Reduction in generation solid waste quantities
3. Reuse of solid waste materials
4. Recovery of materials/metals
5. Generation of energy/biogas
6. Conversion into useful products such as fertilizers, fuel pellets etc
7. Reduction in quantity of solid wastes through incineration/pyrolysis
8. Disposal of solid wastes (land filling)
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