Solid Waste Recycling Composting

Solid Waste Recycling Composting

	Soild Waste Recycling Composting- The utilisation of human and animal solid wastes is of great importance both from the public health and agricultural point of view. Composting is the conversion of the organic fraction of solid waste materials through microbiological processes leading to the production of a humus-like end product that is used primarily as a soil conditioner. The art of composting is very old but in recent years progress has been made in understanding this biological process. These studies have enabled the production of a finished compost which is both valuable and safe from the view point of public health.
There are basically two methods of composting; in the first method, compostable material is placed in pits or in stacks on the ground and the material is turned over at intervals to allow adequate aeration and mixing. This method has proved most satisfactory. In the second method, the waste is filled in pits or trenches in layers and allowed to decompose without being turned over during the composting period of 4.6 months. In big cities where the amount of waste is large, highly mechanized composting plants which handle large quantities of heterogenous wastes containing both compost able and non compostable materials exist. In these plants, garbage is first sorted out, the organics are then crushed, sprayed with sewage and heaped to allow decomposition.
The quality, composition and nature of the wastes available for composting vary widely with the season and region. In villages, the type of waste depends on the type of agriculture, size of the farm, the animals used and the economic condition of the area. In cities, the quantity and quality of waste is determined by the waste products of industry, street sweepings, ash and garbage. There are several factors which affect the composting process since these affect the microbial activity during decomposition. These include the quality of waste, carbon to nitrogen ratio (C/N ratio), moisture content, pH, temperature, aeration, and climatic conditions.
Segregation of waste into compost able and non-compostable materials is often desirable specially with town wastes which contain metal cans, glass, china pieces, concrete, plastics etc. Metal cans and other ferrous metals can be separated by magnetic separators, while other objects can be mechanically removed by screening or by hand picking. Shredding or grinding of organic material for composting is beneficial since shredding makes the material more accessible to microbial attack through increase in the surface area. Decomposition of such shredded material occurs at a faster rate. The decomposition of organic matter is brought about by microorganisms which utilize carbon and nitrogen in the waste for synthesizing cellular constituents. The C/N ratio is, therefore, an important factor determining the rate and extent of decomposition. When excess of carbon is available (C/N ratio is high), the rate of decomposition is slow. Generally, a C/N ratio of 30-40 is considered as optimum.
	During decomposition, a part of the carbon is assimilated and a part is oxidized to carbon dioxide. As a consequence, there is a decrease in the C/N ratio and this decrease in the C/N ratio is an useful index of composting. Moisture is an important factor that determines successful composting. For satisfactory aerobic composting a moisture content of 40-60 percent is desirable. If the moisture content is 40 percent or lower, water can be sprayed during turning. In anaerobic composting (as in the pit method), the maintenance of moisture content is not necessary since there is not much loss from the initial moisture level.

During decomposition, due to microbial activity, a large amount of heat is generated. Normally, a temperature of 45-50°C is reached in the first 24 hours of composting and temperatures of 60-70°C are obtained in 2-5 days.

The decline in temperature is gradual and the high temperature does not persist if the material becomes anaerobic. The creation of aerobic conditions is, therefore, essential to maintain high temperature during the early course of decomposition.

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