Temperature-effect on the performance of non-aerated microalgal-bacterial granular sludge process in municipal wastewater treatment

This paper investigated the performance of non-aerated microalgal-bacterial granular sludge (MBGS) process in municipal wastewater treatment at different temperatures. Results showed that the 70.5%, 81.9% and 86.1% of chemical oxygen demand (COD) could be removed at 15, 22 and 30 °C, respectively, indicating that a high temperature favored removal of organics due to promoted biomass growth. It was found that most of ammonia-N was removed via microbial assimilation by microalgae and bacteria in granules, with bacterial assimilation being dominant at the lower temperature. The phosphorus removal efficiency of 90.1% was achieved at 22 °C, with the presence of abundant Leptolyngbyales, a potential phosphorus accumulating alga. Chlorophyta grew much faster than Leptolyngbyales at 30 °C in microalgal-bacterial granules. It can be concluded that the contributions of microalgal and bacterial assimilations toward COD, ammonia and P removal appeared to be temperature-dependent, i.e. temperature could alter the symbiotic relationship between microalgae and bacteria. This study would contribute to the application of non-aerated MBGS process in municipal wastewater treatment with seasonal variation of temperature.