Effect of bacteria-to-algae volume ratio on treatment performance and microbial community of a novel heterotrophic nitrification-aerobic denitrification bacteria-chlorella symbiotic system.

• HN-AD bacteria and microalgae firstly combined to construct a novel symbiotic system. • The optimal volume ratio was 1/3 and TN and TP removal increased by 28.9% and 67.6%. • Ammonia tolerance of algae increased to 500 mg/L and gas–water ratio decreased to 50. • Halomonas and Rhodocyclaceae play key roles in nitrogen and phosphorus removal. • NarG, narH and narL genes are the main nitrogen removal genes of key HN-AD bacteria. A novel symbiotic system combined by heterotrophic nitrification-aerobic denitrification (HN-AD) mixed bacteria and Chlorella pyrenoidosa was firstly proposed to resolve the poor tolerance and nitrogen removal performance of traditional symbiotic system for treating high ammonia biogas slurry. Results showed that the volume ratio of bacteria to algae had significant effects on nitrogen removal efficiency, microbial community structure, functional bacteria and genes. The optimal ratio was 1/3, and the average removal efficiency of TN and TP increased by 28.9% and 67.6% respectively, compared to those of HN-AD bacteria. High-throughput sequencing indicated nitrogen removal was jointly completed by HN-AD and heterotrophic denitrification. HN-AD bacteria Halomonas and Pseudomonas played a key role in nitrogen removal, and Rhodocyclaceae and Paracoccus took an important part in phosphorus removal. According to the functional gene prediction, the total relative abundance of nitrogen removal genes (0.0127%) and narG, narH and narL genes (0.0054%) were highest in 1/3 system. [ABSTRACT FROM AUTHOR]