Biodegradabilities and Microbial Activities During Composting of Oxidation Ditch Sludge

Abstract

Best design of a compost system is dependent on knowing the degradability of the waste. Although many bulking agents used to adjust moisture and porosity consist of organic matter, it is usually assumed they contribute only a small proportion of the total degradable material in a compost mix. As the microorganisms degrade the organic compounds during composting, it is generally presumed that they grow, and increase in biomass and numbers. In this study, bench-scale compost reactors were used to determine the relative contributions of sewage sludge and the bulking agent (pine sawdust) to the biodegradability of a compost mix. Although the overall level of microorganisms did not change markedly during composting, subpopulations able to degrade selected macromolecules were present at varying levels. Populations capable of degrading bacterial cell walls and thereby of contributing to recycle of inorganic nutrients through biomass turnover were present throughout the composting period.