COMPOSITION AND ACTIVITY OF ACTIVATED-SLUDGE UNDER STARVATION CONDITIONS

The response of activated sludge to starvation was studied in aerobic conditions during a 10 days starvation period. The 30% sludge mass dec rease was related to the degradation of both proteins and polysacchari des as well as to the release of biopolymers in the water surrounding the biomass. After 8 days, organic carbon release as a result of the s ludge degradation was relatively low (almost-equal-to 2%) compared to the respired carbon (42%). The decrease of the total number of bacteri al cells followed the degradation of the solids only after 4 days. The degradation of the sludge constituents occurred with a rapid decrease of the respiratory activity. After 11 days the sludge was still able to use an easily biodegradable substrate (yeast extract) contrary to t he organic matter from primary wastewater. From our results, about 4 d ays of storage of the sludges may represent a limit to be considered f or a high mass reduction and a low biochemical activity loss (allowing the recycling of a viable biomass).