Optimisation of Anaerobically Digested Primary Sludge as a Composting Substrate

The treatment of municipal wastewater in Australia results in the production of 250,000 dry tonnes of raw sewage sludge annually (Beavers, 1993). Two types of raw sewage sludge are produced. Primary sludge consists of settled organic matter from primary wastewater treatment. Secondary sludge is microbial matter produced from the activated sludge process in aeration tanks. In Western Australia, both types of raw sewage sludge are anaerobically digested to reduce pathogens, volatile solids and odour. The residual sludge is then blended for use in potting mixes, prior to land application.