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 ammoniaoxidizing 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.

Automated summary

This study evaluated a novel shortcut biological nitrogen removal method using activated sludge-biofilm coupled with microalgae, achieving high nitrogen removal efficiency and potential to lower operating costs. The algal-bacterial symbiosis improved species richness but reduced microbial diversity of the biofilm, with significant contributions from Nitrosomonas and Thauera in the nitrogen removal process. Additionally, the study indicated that algae and activated sludge coupling increased nitrous oxide emission in the shortcut nitrogen removal process.