Upgrading the MBBR Process to Reduce Excess Sludge Production in Activated Sludge System Treating Sewage

Abstract

Excess sludge production is one of the limitations of the biological activated sludge process. Therefore, the study’s objective is to upgrade the MBBR process to an integrated fixed film-activated sludge (IFAS) process to reduce excess sludge production. Two scenarios were followed in this study to eliminate sludge production in the biological activated sludge process: first, modifying the moving bed biofilm reactor (MBBR) system by increasing the solid retention time (SRT) from 5 to 15 days; and second, upgrading the MBBR process to the integrated fixed-film activated sludge (IFAS) process by applying return activated sludge (RAS) of 50, 100 and 150% with operating hydraulic retention time (HRT) of 6, 12, 14 and 20 h. The results revealed that the first scenario reduced sludge production from 750 to 150 g/day, whereas the second scenario eliminated sludge generation. In the second scenario, operating the system as an IFAS process with complete SRT has eliminated sludge due to sludge decay and cell lysis. In part 3 of the second scenario, the results also showed that the system achieved low effluent pollutants concentrations of 3, 12, 8 and 45 mg/L for BOD, COD, TSS and NO3, respectively. Operating at complete SRT may eliminate sludge production but also result in higher NO3 effluent concentration due to the production of NH3 from sludge decay and cell lysis. To conclude, sludge elimination in an activated sludge system is possible by carefully controlling the process and applying RAS without additional treatment.