BIODEGRADABILITIES AND MICROBIAL ACTIVITIES DURING COMPOSTING OF OXIDATION DITCH SLUDGE

Best design oil a compost system is dependent on knowing the degradabi lity of the waste. Although many bulking agents used to adjust moistur e and porosity consist of organic matter, it is usually assumed they c ontribute only a small proportion of the total degradable material in a compost mix. As the microorganisms degrade the organic compounds dur ing composting, it is generally presumed that they grow, and increase in biomass and numbers. In this study, bench-scale compost reactors we re used to determine the relative contributions of sewage sludge and t he bulking agent (pine sawdust) to the biodegradability of a compost m ix. Although the overall level of microorganisms did not change marked ly during composting, subpopulations able to degrade selected macromol ecules were present at varying levels. Populations capable of degradin g bacterial cell walls and thereby of contributing to recycle of inorg anic nutrients through biomass turnover were present throughout the co mposting period.