Towards a reduction in excess sludge production in activated sludge processes: biomass physicochemical treatment and biodegradation

To decrease activated sludge production, microbial cell lysis can be amplif ied to enhance cryptic growth (biomass growth on lysates). Cell breakage te chniques (thermal, alkaline, acid) were studied to generate Alcaligenes eut rophus and sludge lysates and to evaluate their biodegradability. Gentle tr eatment conditions produced the best results. Complete cell deactivation wa s obtained for temperatures higher than 55 degrees C. The release kinetics were similar for temperatures varying from 60 degrees C to 100 degrees C. A 20-min incubation was suitable for reaching 80% of the maximum releasable carbon. In thermal-chemical hydrolysis, NaOH was the most efficient for ind ucing cell lysis. Carbon release was a two-step process. First an immediate release occurred, which was of the same order of magnitude for A. eutrophu s and sludge [100-200 mg dissolved organic C (DOC) g total suspended solids (TSS)(-1)], followed by a post-treatment release. The second step was virt ually equivalent to the first for sludge, and weaker for A. eutrophus (< 50 mg DOC g TSS-1). The biodegradability of the soluble fraction, both the im mediate and the posttreatment carbon release, was investigated. The optimal degradation yield, obtained with sludge cells, reached 55% after 48 h of i ncubation and 80% after 350 h. The most consistent lysis and biodegradation results occurred at pH 10 and 60 degrees C after a 20-min incubation.