Investigating the mechanism of sludge reduction in activated sludge with an anaerobic side-stream reactor

摘要

To investigate the mechanism of sludge reduction in activated sludge (AS) with an anaerobicnside-stream reactor (ASSR), four AS systems with different digestion schemes were operated innthe laboratory. The four systems are: a) ASþASSR; b) ASþaerobic digester; c) ASþanaerobicndigester; and d) AS with no solids wastage. The average sludge yield of ASþASSR from twonphases was 0.14 mgVSS/mgCOD, which is 22–54% less than that from the three other systems.nThe accounting of biomass in ASþASSR system revealed that 50% of sludge is degraded in ASSRnwhile the other half is degraded in the aeration basin. Furthermore, both whole sludge andncentrate from ASSR led to a significant oxygen uptake in AS, indicating the importance of aerobicnbiodegradation in ASþASSR system. The extracellular polymeric substances (EPS) data showednthat base-extractable EPS was much smaller for AS with ASSR than with no wastage. In contrast,ncation exchange resin-EPS was similar for both systems. These results indicate that degradation ofnbase-extractable EPS accounts for the lower sludge yield in ASþASSR, and based on the literaturenthis organic pool is believed to be aluminium and/or iron-bound EPS. The microbial profile datansuggests that recirculation in ASþASSR selects some unique microorganisms. Further research isnwarranted to study their role in sludge reduction.