Effects of Sludge Holding Tank on the Effluent Quality and Sludge Settling Potential in Conventional Activated Sludge

Excess sludge treatment and disposal is a major challenge for wastewater treatment plants worldwide. In this study, sludge reduction was evaluated using pilot scale sequencing batch reactors (SBRs). Two SBRs were operated alongside each other over a period of 12 months during which time measurements were performed to determine COD, MLSS, MLVSS, pH, DO, SV1, SOUR, and ORP. The results showed that among the different SRT durations (5, 10, 15, 20, 25 days), the 10-day sludge retention time yielded maximum COD removal efficiency (90%) without any bulking or foaming problems. Prior to any reactions taking place in the reactor, the sludge was exposed to various oxidation reduction potentials for 1 to 8 hours in order to determine the effects of uncoupling metabolism on biomass production under different anoxic and anaerobic conditions. COD was observed to decrease from 600 to 33 mg/l while MLSS increased from 1350 to 1500 mg/l over a retention time of 7 hours and for an ORP value of -238 mv. The effluent COD obtained as a result of operating this process was below the limits set by environmental regulations for surface waters and reuse in agriculture. For an ORP value of -238mv, SOUR and SVI were measured to be 22 mgO2/h.gVSS and 40 ml/g, respectively.