Inhibition and recovery of ANAMMOX with Na2SO3: From performance to microbial community analysis

In this study, three concentrations of Na2SO3 solution were used to remove dissolved oxygen in the influent water and enter the up-flow anaerobic sludge bed reactor (UASB). This study investigated the effects of three con-centrations of Na2SO3 on the inhibition and performance recovery of the ANAMMOX system and the structure of the microbial community. The results showed that although Na2SO3 had a deoxidizing function, the ANAMMOX system underwent a sulfate reduction reaction after adding Na2SO3, and the reduction product was mainly H2S, which caused the AnAOB to be inhibited by sulfide. The denitrification performance was less than 1/2 of that under normal conditions. The ANAMMOX system was restored by immediately removing Na2SO3 and reducing nitrogen load. After 11, 20, and 34 days, the performance of the ANAMMOX system returned to normal, but low concentrations(45 mg/L) required a long recovery time. High-throughput sequencing analysis showed that the community of the ANAMMOX system changed significantly. Before and after the experiment, the relative abundance of ANAMMOX functional bacteria Candidatus Brocadia decreased from 32.66% to 21.4%, and Can-didatus Kuenenia decreased from 7.3% to 4.06%. However, the relative abundances of Armatimonadetes and Ignavibacteriae increased from below 2% to about 20%. At the same time, Thiobacillus and Desulfuromonadales were observed. This paper explores and summarizes the cause of Na2SO3's inhibition of AnAOB, highlights the recovery of AnAOB after inhibition for the stable operation and deepens the understanding of the environmental conditions regulating the ANAMMOX process.