Enhanced biological nitrogen removal via dissolved oxygen partitioning and step feeding in a simulated river bioreactor for contaminated source water remediation

In recent years, nitrogen pollution has been increasingly serious in natural waters including drinking source water. A simulated river biofilm reactor fed with contaminated drinking source water was established to evaluate the effects of dissolved oxygen (DO) partitioning and step feeding on the nitrogen removal performance and biofilm microbial community. Results showed that after the hydraulic retention time of anoxic zone extending and step feeding, the effluent concentration of ammonia was below 0.2 mg L−1, and the removal efficiency of total nitrogen increased from 12.02% ± 4.59% to 34.98% ± 2.65%, which indicated the occurrence of simultaneous nitrification and denitrification. The results of denaturing gradient gel electrophoresis showed that the microbial community of biofilm obviously shifted via DO controlling and step feeding. Low DO concentration favored the enrichment of denitrifying bacteria and coexistence of algae and bacteria, and the pattern of step feeding could increase the community abundance. The dominant heterotrophic bacteria species of biofilm in oligotrophic niche belonged to Hyphomicrobium sp., Pseudomonas sp., Chloroflexi sp., Enterobacter sp., Pantoea sp., and Synechococcus sp., which were mostly associated with denitrification and refractory organics utilization. It was worth noting that the ammonia-oxidizing bacteria (AOB) community of biofilm was stable throughout the whole experiment, and Nitrosomonas sp. was the predominant AOB in the oligotrophic niche.

► SND occurs in contaminated source water remediation at low DO level with step feeding.
► Low DO concentration favors the coexistence of functional bacteria and algae in oligotrophic niche.
► Step feeding process could increase the bacteria diversity and enhance denitrification.
►  Functional bacteria related with denitrification and refractory organics utilized are enriched.
► AOB community of the biofilm is stable during the change of DO level and feeding pattern.