Novel shortcut biological nitrogen removal using activated sludge-biofilm coupled with symbiotic algae

This study evaluated a novel shortcut biological nitrogen removal (BNR) method using activated sludge-biofilm coupled with microalgae in a photo-sequencing batch biofilm reactor (PSBBR) for treating high ammonia nitrogen (NH4+-N) wastewater. Results showed that the symbiotic microalgae supplied oxygen and an additional organic carbon source for bacteria. The consortium achieved high nitrogen removal efficiency (> 90%) and had the potential to lower the operating cost when used for treating biogas slurry (BS). It saved more than 50% of the external carbon source and reduced about 78% of oxygen demand compared with the conventional BNR process. Nitrogen was removed mainly through shortcut nitrification-denitrification (SCND) (> 80%) and biological assimilation (6.8%) in the PSBBR. The algal-bacterial symbiosis improved the species richness but reduced the microbial diversity of the biofilm. Nitrosomonas with an abundance of 19.81% was the dominant ammonia-oxidizing bacteria (AOB) in the biofilm, while Thauera with an abundance of 45.03% played a leading role in denitrification. This study concurrently indicated that algae and activated sludge coupling increased the nitrous oxide (N2O) emission in the shortcut nitrogen removal process.