Biological Degradation

Biological Degradation

	Biological Degradation - There are different methods of composting the commonly used local method involves piling up of the substrates into large heap. Bulking agents like large wood chips or barks can be mixed with the substrates to facilitate aeration. After the required period of composting, about 21 days, bulking agents are separated from the compost and the compost is ready for use. The most primitive and simplest method is to pile the material into windrows, which are heaps resembling pyramids. Windrows are of about 3cm high with a base of 9m width. The mixture is turned regularly with mechanical shovels to promote aeration. After four to six weeks, depending on moisture and climate, a stable compost is formed.
Windrow composting has a number of disadvantages. Since it is done in the open air it is significantly affected by the local climate. Often the compost generates odors which may be difficult to control and this may rise complaints from local people. Windrow composting requires large land area and therefore unsuitable for urban. An alternative method of composting involves mechanical mixing and aeration inside closed digesters. A number of processes are used in mechanical composting and all of them have equipments to control temperature, pH and C : N ratio. The most well known process is the Dano process. This employs drums which are about 30m long and 5 m in diameter. The drums rotate slowly to facilitate mixing and aeration. The advantages of these mechanical composting are (1) they do not suffer the problems of windrow composting (2) with better control over mixing, aeration and temperature the composting process can be completed in a shorter period than that required for windrow composting.

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