| Excess biomass generated during municipal wastewater treatment using biological activated sludge processes is one of the main drawbacks of treatment processes. In this study, two sequencing batch reactors (SBRs) were operated and monitored to evaluate, (1) the long-term sustainability of sludge reduction and nutrient removal and (2) fate of carbon in the lab scale reactors as well as in full scale plants run under similar sludge reduction modes. One of the lab scale reactors (called control SBR) was run in standard operational mode at 10-day solids retention time (SRT) while the other reactor (called modified SBR) was run in sludge minimizing mode at nearly 100-day SRT to induce the anaerobiosis of the returned biomass in a sidestream reactor. Furthermore, to compare the overall biomass yields in both reactors, the wasted biomass from the conventional reactor was taken to a conventional anaerobic digester. Overall, both reactors achieved an average PO43−-P removal of 85%, NH3-N removal of 99%, and 100% chemical oxygen demand (COD) removal. The modified SBR consistently showed a biomass yield of 0.136gVSS/gCOD as compared to the control SBR which maintained a biomass yield of 0.34gVSS/gCOD. Overall, the modified SBR generated 60% less biomass than the control SBR. Carbon mass balance and partitioning experiments based on C13 substrate showed that both modified SBR and the associated sidestream reactor showed better mineralization in terms of CO2 production. Furthermore, for the modified SBR, less C13 partitioned into biomass and more C13 went into head space in the form of CO2, thus suggesting why modified SBR enabled low biomass yield. A similar trend was observed for full scale missed liquor samples. |
