Investigating the mechanism of sludge reduction in activated sludge with an anaerobic side-stream reactor.
ABSTRACT To investigate the mechanism of sludge reduction in activated sludge (AS) with an anaerobic side-stream reactor (ASSR), four AS systems with different digestion schemes were operated in the laboratory. The four systems are: a) AS+ASSR; b) AS+aerobic digester; c) AS+anaerobic digester; and d) AS with no solids wastage. The average sludge yield of AS+ASSR from two phases was 0.14 mgVSS/mgCOD, which is 22-54% less than that from the three other systems. The accounting of biomass in AS+ASSR system revealed that 50% of sludge is degraded in ASSR while the other half is degraded in the aeration basin. Furthermore, both whole sludge and centrate from ASSR led to a significant oxygen uptake in AS, indicating the importance of aerobic biodegradation in AS+ASSR system. The extracellular polymeric substances (EPS) data showed that base-extractable EPS was much smaller for AS with ASSR than with no wastage. In contrast, cation exchange resin-EPS was similar for both systems. These results indicate that degradation of base-extractable EPS accounts for the lower sludge yield in AS+ASSR, and based on the literature this organic pool is believed to be aluminium and/or iron-bound EPS. The microbial profile data suggests that recirculation in AS+ASSR selects some unique microorganisms. Further research is warranted to study their role in sludge reduction.
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ABSTRACT: Enzyme additives are believed to improve septic tank performance by increasing the hydrolysis and digestion rates and maintaining a healthy microbial population. Previous studies reported mixed results on the effectiveness of enzymes on mesophilic and thermophilic digestion, and it is not clear whether enzymes would be effective under septic tank conditions where there is no heating or mixing, quantities of enzymes added are small, and they can be washed out quickly. In this study, batch reactors and continuous-flow reactors designed and operated as septic tanks were used to evaluate whether enzymatic treatment would increase the hydrolysis and digestion rates in primary sludge. Total solids, volatile solids, total suspended solids, total and soluble chemical oxygen demand, concentrations of protein, carbohydrate, ammonia and volatile acids in sludge and effluent samples were measured to determine the differences in digestion rates in the presence and absence of enzymes. Overall, no significant improvement was observed in enzyme-treated reactors compared with the control reactors.Bioprocess and Biosystems Engineering 05/2012; 35(9):1577-89. · 1.87 Impact Factor