A comparative study of algal-bacterial granular sludges and aerobic granular sludge at different C/N ratio: Granule characteristics, SND progress and Microbial community

Abstract

The algal-bacterial synergistic effect in algal-bacterial granular sludge (ABGS) made its nitrogen metabolism mechanism different from that of aerobic granular sludge (AGS). In this study, the effects of algae on granules characteristics, SND process and community structure in ABGS were studied by treating wastewater with different C/N (13:1–20:1) ratios. The results showed that ABGS and AGS had excellent nitrogen removal capacity of 86 % and 91 %, respectively, and SND efficiency was above 90 %. ABGS granules were looser due to the phototaxis of algae, and the oxygen penetration depth was higher than that of AGS. The NH4+-N removal efficiency of AGS was higher than that of ABGS, but the SND efficiency of ABGS was better than that of AGS. In ABGS, photosynthesis provided organic carbon for denitrification in anaerobic period, and organic carbon might be more important than strict anaerobic environment. In aerobic period, The SND process in ABGS was mainly heterotrophic nitrification aerobic denitrification (HAND), while in AGS was conventional simultaneous nitrification denitrification (CSND). The results of this study would provide a theoretical foundation for further understanding the difference between ABGS and AGS nitrogen removal mechanisms and help to further expand the application of ABGS in practical engineering.