Operational Evaluation of Pilot-Scale Side-Line Treatment Based on Microbial Population and Activity

Abstract

A pilot-scale study conducted in a municipal wastewater treatment plant (WWTP) for short-cut biological nitrogen removal (SBNR) from anaerobic reject water (ARW) was evaluated based on the microbial population and activity to assess optimum operational modes and effective parameters. Two main periods, one- and two-stage sequential batch reactor (SBR) systems, were operated at multiple-feeding mode + high sludge age + ambient temperature (during hot and cold seasons) and two separate process/reactor configurations with back feeding + controlled temperature (20°C, 25°C, 30°C, and 35°C) conditions, respectively. One-stage SBR operation at high temperature, moderate hydraulic retention time (HRT), and multiple-feeding mode promoted high sludge age and bacterial count and activity at the highest level for ammonium-oxidizing bacteria (AOB) and denitrifying bacteria (DB) where other species common in municipal WWTPs, Actinobacteria (filamentous bacteria) and Accumulibacter (phosphate-removing bacteria), dropped substantially in population number. Nitrospira was the only nitrite-oxidizing bacteria (NOB) species detected, ranging at the lowest level during the one-stage SBR operation period, showed a tendency to wash out, and rose in population in the full aerobic SBR of the two-stage operation. An overall bacterial activity and viability loss obtained in the two-stage SBR operation resulted in reduced sludge age values with a severe deterioration in the denitrifying anoxic SBR (AnSBR), which was correlated with the limited level of suitable substrate, thus, starving condition. The contribution of the anaerobic bacteria activity and slowly degrading organic matter oxidation in the one-stage SBR operation was pronounced in the study where the sludge age obtained was found as the most significant parameter in comparison with temperature and HRT.