Ammonia stress and mechanistic impact on NO2- and S0 accumulation in a double short-cut sulfur autotrophic denitrification (DSSADN) system

Double short-cut sulfur autotrophic denitrification (DSSADN), targeting the accumulation of NO₂^--N and S⁰, not only enhances the nitrogen removal efficacy of the Anammox process but also avoids SO₄^2- contamination. Ammonia is an important inhibitor faced by the DSSADN coupled anammox process. This study explores the effects of different ammonia concentrations and forms on nitrogen and sulfur conversion, functional enzyme activities and microbial communities in the DSSADN process. Results indicate that at an NH₄⁺-N concentration of 106 mg/L (22 mg/L free ammonia (FA)), the relative abundance of nirK decreases, promoting NO₂^--N accumulation up to 95 %. When NH₄⁺-N reached 298 mg/L (62 mg/L FA), the relative abundance of soxB declined, which promoted an increase in S⁰ accumulation to 92 %. When NH₄⁺-N reached 250 mg/L (52 mg/L FA), the abundances of both narG  and sqr decreased, leading to inhibited NO₂⁻-N reduction and S^2- oxidation, and decreasing the removal rates of NO₂⁻-N and S^2-. The performance of the DSSADN system can be fully restored by reducing the FA concentration through the pH. With the increased FA concentration, Sulfurimonas gradually increases, while Thiobacillus decreases.