Efficient nitrogen removal in separate coupled-system of anammox and sulfur autotrophic denitrification with a nitrification side-branch under substrate fluctuation

Abstract

In order to achieve efficient nitrogen removal, a separate coupled-system of anaerobic ammonia oxidation (anammox) and sulfur autotrophic denitrification (S0-SADN) was established. In this study, the operational feasibility and stability of the coupled-system under substrate fluctuations were investigated. Results showed that the coupled-system improved the total nitrogen removal efficiency (TNRE) to 99.15 ± 0.68%. The tryptophan-like substances in anammox effluent positively impacted the growth of the S0-SADN biofilm. This positive cooperativity boosted the S0-SADN to achieve rapid 12-day startup and stable operation thereafter. The TNRE was determined at 95.27 ± 1.51% and 93.44 ± 0.96% under excessive nitrite and ammonium, respectively. The coupled-system recovered quickly after 21 days of starvation deterioration. To further treat the excessive ammonium, the nitrification side-branch of the coupled-system improved the TNRE to 99.08 ± 0.68%. Extracellular polymeric substances analysis revealed that the anammox and S0-SADN bacteria secreted protein-like substances to resist substrate fluctuation. Microbial community analysis indicated that the stability of bacterial community supported the stability of the coupled-system. These results collectively suggested that the separate coupled-system exhibited excellent performance and provided a platform for practical wastewater treatment in future.