| Description |
Sludge reduction at source for the sludge minimization through fasting and feasting has been practiced with activated sludge processes over the past few decades. In this research, two sequencing batch reactors (SBRs) were operated aiming to investigate the possibility of simultaneous sludge reduction and nutrient removal using both synthetic and real wastewater. One of the lab-scale reactors (called the control-SBR) was run in a standard operational mode at 10-day solid retention time (SRT), while the other reactor (called the modified-SBR) was run in a sludge minimizing mode to induce the anaerobiosis of the returned biomass in a sidestream reactor. Furthermore, to compare the overall biomass yields in both reactors, the waste biomass from the control-SBR was taken to a conventional anaerobic digester. Both SBRs were fed with synthetic wastewater, and then changed to real primary effluent in a step-wise manner from one municipal wastewater treatment plant (WWTP), and then it was fed with the raw wastewater (after being screened) from another WWTP. Overall, both reactors achieved a higher than 80% of PO43--P removal and 95% of NH4+-N removal. The modified system generated 60% less biomass than the control system with synthetic wastewater. The sludge reduction achieved in the modified system was 39% and 35%, compared to the control system, when the reactors were fed with real primary effluent and raw wastewater, respectively. Carbon mass balance and partitioning experiments showed that the modified-SBR had better mineralization in terms of CO2 production. In the modified-SBR, less 13C partitioned into biomass and more 13C went into the headspace in the form of CO2, thus suggesting why modified-SBR achieved a lower biomass yield. Furthermore, modified-SBR contained more diverse ammonia oxidizing bacteria and polyphosphate accumulating bacteria (PAOs) than in the control-SBR. Since it contained more slow growing bacteria (Nitrospira, Mesorhizobium and Candidatus Accumulibacter) and filamentous bacteria (unclassified Cytophagales), this could be another possible mechanism of sludge reduction in the modified-SBR. Two Dechloromonas-related operational taxonomic unites (OTUs) were detected in both SBRs, as the denitrifying PAOs that could utilize nitrite or nitrate to remove phosphorus without any extracellular carbon substrates under anoxic conditions. |
