Effects of side-stream, low temperature phosphorus recovery on the performance of anaerobic/anoxic/oxic systems integrated with sludge pretreatment.

Introduction of sludge reduction practices in enhanced biological phosphate removal (EBPR) often leads to a decrease in phosphorous (P) removal efficiency. In this study, an attempt has been made to develop sustainable P removal in an anaerobic/anoxic/oxic (AAO) system integrated with sludge reduction by incorporating side-stream P recovery. Two AAO reactors, one acting as a control (CAAO) and the other as an experimental system (EAAO), were used in our experiment. The average P solubilisation efficiency and its recovery from thermally pre-treated sludge were found to be 28% and 99%, respectively. The P recovery process prevented the biomass in the EAAO system from reaching its threshold level and resulted in sustainable P removal throughout the study period. Thermochemical pre-treatment, at a rate of 1.5% Q in the EAAO reactor, was responsible for a 28% reduction in the amount of sludge produced. The yield observed (Y obs) values for the system with and without pre-treatment were found to be 0.28 and 0.22 kg MLSS/kg COD, respectively. An initial 50 days of reactor operation was utilised to stabilise the systems (Phase 1). The total nitrogen removal during Phase 2 (51-225 days) was slightly higher than that in Phase 1 (76-80% and 68-75%, respectively). The MLSS/MLVSS ratios of both systems were identical and were between 78% and 83% for both the CAAO and EAAO. The effluent COD concentration was not significantly affected by the proposed method of treatment. From the results of the present study, it is concluded that the proposed mode of treatment was capable of both sustainable removal of P and control of excess sludge production.