Waste disposal – A burning problem to be resolved to save environment:
The disposal of garbage in the world is a problem. This problem continues to grow with the growth of population and development of industries. Disposal of waste in open pits has become routine in majority of places.
Waste can be many different types. The most common methods of classification are by wastes’ physical, chemical and biological characteristics. One important classification is by their consistency, such as solid, liquid and semisolid or sludge.
(i) Solid wastes are waste materials that contain less than 70% water. This class includes such materials as household garbage, some industrial wastes, some mining wastes, and oilfield wastes such as drill cuttings.
(ii) Liquid wastes are usually wastewater's that contain less than 1% solids. Such wastes may contain high concentrations of dissolved salts and metals.
(iii) Sludge is a class of waste between liquid and solid. They usually contain between 3% and 25% solids, while the rest of the material is water dissolved materials.
There are many different methods of disposing of waste; such as Landfills, refuse burning in incinerators etc.
(a) Landfill is the most common and probably accounts for more than 90 percent of the nation's municipal refuse. Landfills have been proven contaminates of drinking water in many areas. Landfills are the most cost affective method of disposal, with collection and transportation accounting for 75 percent of the total cost. In a modern landfill, refuse is spread thin, compacted layers covered by a layer of clean earth. Pollution of surface water and groundwater is minimized by lining and contouring the fill, compacting and planting the uppermost cover layer, diverting drainage, and selecting proper soil in sites not subject to flooding or high groundwater levels. The best soil for a landfill is clay because clay is less permeable than other types of soil. Materials disposed of in a landfill can be further secured from leakage by solidifying them in materials such as cement, fly ash from power plants, asphalt, or organic polymers.
(b) Refuse is also burned in incinerators. It is more expensive but relatively safer method of disposal than landfills. It has also been reported that, garbage burned in incinerators has poisoned air, soil, and water. Modern incinerators are designed to destroy at least 99.9% of the organic waste material they handle. Numerous thermal processes recover energy from solid waste. Companies burn in-plant wastes in conventional incinerators to produce steam. Pyrolysis, a process of chemical decomposition, produces a variety of gases and inert ash. These gases then are used for manufacturing some useful chemicals. Recently, in some countries oil also has been produced successfully from plastic garbage. This conversion is a very useful conversion and we should try to convert plastic garbage into useful oil.
(c) Organic materials that have little or no heavy metals can be detoxified biologically. Composting and land farming, in which materials are spread out over a large land area so that microbes can decompose them, are examples of biological treatment of hazardous waste. If the materials are not detoxified before they percolate into groundwater than obvious repercussions may occur. Composting includes preparing refuse and breakdown of organic matter by aerobic microorganisms.
(d) The practice of recycling solid waste is an old one. Metal implements were melted down and recast in prehistoric times. Today, recyclable materials are recovered from municipal refuse by a number of methods, including shredding, magnetic separation of metals, screening, and washing.
(e) Hazardous wastes pose a danger to humans or other living organisms. Management of radioactive and other hazardous wastes is subject to Govt. regulation. No satisfactory method has yet been demonstrated for disposing permanently of radioactive wastes.
Further discussions on problems waste disposal: There is a strong movement in many countries to reduce the volume of wastes to be dumped. The increase of composting sites is an indication that organic fraction of garbage can be converted into a useful and commercial product with a higher value. For inert materials, technologies are needed to use wastes as raw materials to produce new products. Development of new materials from recycled materials will also encourage sorting of solid wastes. "Zero Waste" movement also targets industries and waste exchange. 40 % of landfilled wastes in most of the countries come from building materials and this suggests that such wastes can be avoided by developing long-lasting materials and dwellings to reduce wastes from need to rebuild. Other alternatives and efforts indicate that
(i) Onsite treatment and utilization will reduce need for transport.
(ii) Waste minimization is a socially desirable goal.
(iii) Subsidy on products generated from recycled materials will encourage socio-economic changes.
(iv) Centers with technologies that use collected waste materials are needed.
(v) Wastes that have severe risks and excessive problems in disposal should be identified and those which cannot be neutralized may need to be restricted at the point of creation or entry.
(vi) A database on wastes that are available will provide information to possible users of wastes.