Windrowing: The windrowing is an aerobic composting system in which long trapezoidal shaped heaps known as windrow are placed on hard clay base/concrete floor with the provision of drains. Impervious water from the surface of windrows are collected in effluent treatment plant (ETP). All unprotected windrow areas are provided with an impermeable base that is made of concrete or of compacted clay. Such base should have a thickness of not less than 50 centimeters and the permeability less than 10 cm per second. The slope of the floor base must be in the ratio of 1: 2 and must be accompanied by lined drains so that leach ate and runoff water can be collected. The lined drains are connected with lined settling pond, where qualities of waste-water are tested on a weekly basis. A treatment unit is provided to regulate the standard of the waste water before it is discharged to open drains. The photograph of the windrow piles from Global Waste Research Institute (GWRI) is shown in Figure 4.
In this system, waste of 50 tons can be processed per day, but for this large area land of about 100 m x 90 m is requiring. For windrow composting of 50 ton waste around 20 windrows will require. The size of each windrow is 3m long x 2m wide x 1.5m high, the total volume should not exceeding 9.0cu.m (Saleem, 2009).
Each windrow must be turned at every 6th & 11th days either by mechanical or manually means. While doing this insect’s larvae get destroyed and help in aeration. On the 16th day, broken windows are passed through a manually operated rotary screens square mesh of size about 25mm to remove the oversize materials. The material retained in 25 mm sieve is rejected and dump to land fill site. The material that is passing through 10mm sieves, but retained on 4 mm sieve is grade II compost. The material that passes through 4 mm sieve is grade I compost. The screened compost is kept on stored for about 30 days in heaps to ensure stabilization before the sale (Saleem, 2009).