Effect of S2O32−-S addition on Anammox coupling sulfur autotrophic denitrification and mechanism analysis using N and O dual isotope effects

Abstract

Anaerobic ammonia oxidation (Anammox) coupling sulfur autotrophic denitrification is an effective method for the advanced nitrogen removal from the wastewater with limited carbon source. The influence of S2O32−-S addition on Anammox coupling sulfur autotrophic denitrification was investigated by adding different concentrations of S2O32−-S (0, 39, 78, 156 and 312 mg/L) to the Anammox system. The contribution of sulfur autotrophic denitrification and Anammox to nitrogen removal at S2O32−-S concentrations of 156 mg/L was 75% ∼83% and 17%∼25%, respectively, and the mixed system achieved completely nitrogen removal. However, Anammox bioactivity was completely inhibited at S2O32−-S concentrations up to 312 mg/L, and only sulfur autotrophic denitrification occurred. The isotopic effects of NO2−-N (δ15NNO2 and δ18ONO2) and NO3−-N (δ15NNO3 and δ18ONO3) during Anammox coupling sulfur autotrophic denitrification showed a gradual decrease trend with the increase of S2O32−-S addition. The ratios of δ15NNO2:δ18ONO2 and δ15NNO3:δ18ONO3 was maintained at 1.30–2.41 and 1.36–2.52, respectively, which revealed that Anammox was dominant nitrogen removal pathway at S2O32−-S concentrations less than 156 mg/L. Microbial diversity gradually decreased with the increase of S2O32−-S. The S2O32−-S addition enhanced the S2O32−-driven autotrophic denitrification and weakened the Anammox, leading to a gradually decreasing trend of the proportion of Candidatus Brocadia as Anammox bacteria from the initial 27% to 4% (S2O32−-S of 156 mg/L). Yet Norank-f-Hydrogenophilaceae (more than 50%) and Thiobacillus (54%) as functional bacteria of autotrophic denitrification obviously increased. The appropriate amount of S2O32−-S addition promoted the performance of Anammox coupling sulfur autotrophic denitrification achieved completely nitrogen removal.