Composting of municipal sewage sludge mixed with rice hulls

A mixture of undigested sludge cake with ground rice hulls as a bulking material was composted, and the changes in various properties of the mixture during active composting and curing were studied using a newly devised experimental apparatus for composting. The essential results obtained were as follows. 1. The temperature of the mixture was rapidly raised to 60°C by active composting and this level was maintained for more than 10 hr.2. The concentration of gaseous NH3 and CO2 in the off-gases increased soon after initiation of the active composting and decreased to a low constant level on the 14th day, when the active composting was judged to be finished.3. The BOD3 sharply decreased until the end of the active composting and maintained a low constant level thereafter.4. The ignition loss gradually decreased during curing. These changes were found to be useful as indices for checking the process of composting.