Flowsheet
In the pre-fermentation type of plant which are preferred, in a majority of Indian urban centres, the incoming trucks can directly discharge their contents in the windrow area.
During composting, the temperature of the mass has to be continuously monitored. This can be done by using probes. The optimum moisture content for composting is between 50-60%, while that in the incoming waste is much lower. The addition of moisture can hence be done through a hose connected to a fire hydrant. During composting, the moisture content tends to reduce and necessary moisture can be similarly added during turning.
After 20 days, the organic matter would be stabilised and the waste can then be taken for further processing.
The Indian waste characteristics indicate a low content of metals and glass.
Further, when the recommendations of the committee appointed by Hon’ble Supreme Court regarding source separation are implemented, this proportion will be very small. Magnetic separators hence need not be provided. The glass, plastics and other inorganics can easily be removed using the manual separation process and ballistic separators will not be required. After pre-fermentation, the waste is transferred to a hopper using tractor trailor system. A conveyor at the bottom of the hopper transfers it to the sorting area where workers standing on either side of the conveyor belt remove the contraries and deposit them in bins placed alongside. As majority of Indian urban centres are not completely sewered, human excreta and cowdung are often mixed with the waste. After prefermentation, the material is no more offensive and hence does not pose any problem during manual separation.
The compost thus prepared can be sold directly to the farmers as raw or green compost. However, as the lignin content of the waste has not yet been stabilised, it should not be applied to the farms for at least two more months. In case adequate space is available at the plant, the material should be stored in large size maturation windrows for 2-3 months. During this period, lignin and other resistant material is stabilised and the product can then be sold as ripe compost.
In case the ripe compost is to be sold in bulk it can be sold as it is.
Sometimes it is sold in small packets. In such cases, from marketing point of view, size reduction using a simple hammer mill is carried out and the material is bagged and sold. As the material is already stabilised, the required Horse Power of the hammer mill is less, thus reducing the energy consumption and maintenance problem.
In the North East Indian states, to protect the windrows from heavy rainfall, the windrow area will have to be covered. For urban centres in Kashmir and Himachal Pradesh covering of windrows will be necessary to protect the plant from low external temperatures.
