Biological nutrient removal in a sequencing batch membrane bioreactor treating municipal wastewater

This study aimed to evaluate the performance of a sequencing batch membrane bioreactor (SBMBR) in wastewater treatment for nutrient removal. The reactor, which was built at a pilot scale with a volume of 15L, was operated for 240d and fed with municipal wastewater. The SBMBR was operated under a sequencing batch mode, with a total cycle time of 4h, including the feeding, anoxic/anaerobic, and aeration/filtration phases. The membrane bioreactor presented high performance on chemical oxygen demand, ammonium, and total nitrogen removal during the whole experimental period, with average removals efficiencies of around 97, 99, and 82%, respectively. Regarding total phosphorus, SBMBR reached the average removal efficiency of 48%. The poor phosphorus removal performance was attributed to the low availability of organic matter during the anoxic/anaerobic phase due to denitrification activity, which limited the P-release process and subsequent P-uptake during aerobic phase. Furthermore, the temperature increase during the summer period further hindered the enhanced biological phosphorus removal process, in which a decrease in the P-release values was observed. Fluorescence in situ hybridization analysis revealed a large presence of glycogen-accumulating organisms population on the SBMBR sludge, which contributes to explain the low efficiency obtained in phosphorus removal.