Excess sludge disposal is one of the serious challenges in biological wastewater treatment. Reduction of sludge production would be an ideal way to solve sludgeassociated problems rather than the post-treatment of the sludge produced. In this study, a new wastewater treatment process combining anaerobic/anoxic/oxic system with thermochemical sludge pretreatment was tested in a laboratory scale experiment. In this study, the effects of the sludge pretreatment on the excess sludge production in anaerobic/anoxic/oxic were investigated. The system was operated in two Runs (1 and 2). In Run 1, the system was operated as a reference and in Run 2, a part of the mixed liquid was pretreated thermochemically and was returned to the bioreactor. The average solubilization efficiency of pretreated sludge was found to be about 35 % during the study period of 220 days. Sludge production rate in Run 2 was less than that in Run 1 by about 52 %. Total phosphorous was removed by enhanced biological phosphorous removal with the removal efficiency of 83-87 % and 81-83 % for Run 1 and Run 2, respectively. Total nitrogen removal in Run 2 (79-82 %) was slightly higher than that in Run 1 (68-75 %). The mixed liquor suspended solids/ mixed liquor volatile suspended solids ratio was identical after both runs in the range 78-83 %. The effluent water qualities were not significantly affected when operated with thermochemical pretreatment at pH 11 and 60°C for 3 h during 7 months. From the present study it is concluded that thermochemical sludge pretreatment of anaerobic/anoxic/ oxic process plays an important role in reduction of sludge production.

ABSTRACT:In the present study, two bench-scale anaerobic/ anoxic/ oxic submerged membrane bioreactors were used to study the effect of thermochemical sludge disintegration system on the excess sludge production. Among the two membrane bioreactors, one was named experimental membrane bioreactor and another one was named as control membrane bioreactor, where a part of the mixed liquor was treated with thermo chemical and was returned back to membrane bioreactor. Thermo chemical digestion of sludge was carried out at fixed pH (11) and temperature (75 °C) for 24 % chemical oxygen demand solution. The other one was named control membrane bioreactor and was used as control. The reactors were operated at three different mixed liquor suspended solids range starting from 7500 mg/L to 15000 mg/L. Both of membrane bioreactors were operated at a flux of 17 LMH over a period of 240 days. The designed flux was increased stepwise over a period of one week. During the 240 days of reactor operation, both of membrane bioreactors maintained relatively constant transmembrane pressure. The sludge digestion had no impact on chemical oxygen demand removal efficiency of the reactor. The results based on the study indicated that the proposed process configuration has potential to reduce the excess sludge production as well as it didn't deteriorate the treated water quality.

In this present study, an aerobic submerged membrane bioreactor (MBR) was used to study the effect of thermochemical pretreatment on the efficiency of sludge reduction. For this purpose, two MBRs were fabricated. Between the two MBRs, one acted as a control reactor (CMBR) and the other acted as an experimental reactor (EMBR). The MBRs were operated with a mixed liquor suspended solids (MLSS) concentration in the range of 6,800-7,200 mg/L for a period of 160 days. In the EMBR, part of the MLSS was withdrawn at a ratio of 1% of Q and was pretreated by low temperature thermochemical treatment. The sludge pretreatment was carried out at 60 W C and an alkali dosage in the range of 0.49 to 0.56 mg NaOH/mg MLSS. During the pretreatment, 42% of COD solubilization and 22% of SS reduction were observed. The pretreated sludge was returned to the reactor for further degradation where it was found to be 42% reduced. During the 160 days of reactor operation, both of the MBRs maintained a relatively constant transmembrane pressure. The sludge digestion does not have any impact on the COD removal efficiency of the reactor.