Factors affecting Composting Process - 3
14.4.6 Aeration
It is necessary to ensure that oxygen is supplied throughout the mass and aerobic activity is maintained. During the decomposition, the oxygen gets depleted and has to be continuously replenished. This can be achieved either by turning of windrows or by supplying compressed air. During the turning, it is necessary to bring inner mass to the outer surface and to transfer the outer waste to the inner portion. (Fig. 14.2) . In case of artificial air supply the quantity of air supply is normally maintained at 1-2 cu.m./day/kg of volatile solids.
Artificial air supply requires enclosing decomposing mass in containers which is quite costly. Hence in Indian conditions the decomposition is commonly carried out in open windrows. Studies at NEERI have shown that the optimum turning interval which will reduce the cost and simultaneously maintain aerobic conditions is 5 days.
14.4.7 Addition of Sewage and Sewage Sludge
The optimum C/N ratio for composting is 25-30. MSW in developed countries has a C/N ratio of nearly 80. To bring it down to the optimum value and to reduce the cost of sewage sludge treatment, it is mixed with sewage sludge (C/N = 5 to 8). MSW in India, on the other hand has an initial C/N ratio of around 30 which does not need blending. If such a mixing is done, C/N value may reduce below 20, when a loss of nitrogen in the form of ammonia occurs. (Table 14.2)
Addition of sewage sludge increases smell and odour problems. It will also increase handling and transportation cost. Even if sewage is used as a source of moisture, bulk of sewage will still have to be treated. The sewage often contains waste waters from industries which contain hazardous constituents which will pose problems in the composting process and compost quality. In view of the above, addition of sewage and sludge is not desirable in India.
