The Comparison of Biological Sludge Reduction Processes

Five Activated Sludge Process (ASP) systems with different side-stream bioreactor (SSR) and digestion schemes were operated in the laboratory to compare biological sludge reduction processes. The five systems are: #1) ASP+AerSSR; #2) ASP+AnaSSR; #3) ASP+aerobic digester; #4) ASP+anaerobic digester; and #5) ASP with no solids wastage. In Phase I, the overall sludge yields of #1(ASP+AerSSR) and #2 (ASP+AnaSSR) was 0.11 and 0.18 mgVSS/mgCOD, respectively. In Phase II, the accounting of biomass in AS+ASSR system revealed that about 54% of sludge is degraded in ASSR while about 46% of sludge is degraded in the ASP. The extracellular polymeric substances (EPS) data showed that base-extractable EPS was much smaller for AS with AnaSSR (#2) than the others. These results indicate that degradation of base-extractable EPS accounts for the lower sludge yield in AS+AnaSSR, and based on the literature these organic pool are believed to be aluminum and/or iron-bound EPS. The overall sludge yield of #1 (ASP+AerSSR) was similar with #2. CER-extractable EPS of #1 was smaller than the others. It is thought that divalent cations associated EPS was degraded through #1. Microbial community data from DGGE analysis showed that there are some common and different microbial cells between side-stream bioreactors and the conventional digesters. This result may suggest that side-stream bioreactors are able to select some unique microbial cells. Further research is underway to study their identification and role and fate in biological sludge reduction system.