Treatment of nitrogen-rich wastewater by mixed aeration combined with bioaugmentation in a sequencing batch biofilm reactor: Biofilm formation and nitrogen-removal capacity analysis

Abstract

The mixed aerated and bioaugmented sequencing batch biofilm reactor (SBBR) was developed to improve the efficiency of nitrogen-rich wastewater treatment, and the mechanism of biofilm formation and nitrogen removal was analyzed. The results showed that the addition of aerobic denitrifiers could shorten the start-up time and significantly improve the biofilm formation ability of SBBRs. The presence of nanobubbles could make the biofilm more compact and secrete more EPS, which promoted the activity and stability of the biofilm. During the stable operation stage, the bioaugmented SBBR under mixed aeration mode showed the best nitrogen removal performance and the removal rates of NH4+-N (95.65) and TN (94.88%） were increased by 19.86% and 14.36% compared with the control group, respectively. Microbial community structure and nitrogen metabolism pathway analysis revealed that strain ZS1 colonized the reactor. Hyphomonas, Defluviicoccus and Hydrogenophaga played important roles in N removal in the mixed aerated and bioaugmented SBBR. Meanwhile, the suitable oxidative environment created by mixed aeration made autotrophic nitrifiers（mainly Nitrospira and Nitrosomonas）and aerobic denitrifiers (mainly Hydrogenophaga, Hyphomonas and Pseudofulvimonas) coexist successfully, increasing the relative abundance of the key functional genes (amoABC, hao, napAB genes) in nitrification and denitrification processes to improve the N removal performance. Furthermore, mixed aeration combined with bioaugmented stimulated the nirA, gltBD and GLUD genes, thus promoting the process of nitrogen assimilation and providing a pathway of the direct removal of NH4+-N.