Insight into nitrogen removal through sulfate reducing anaerobic ammonia oxidation coupled with sulfur cycle: A...

Sulfate reducing anaerobic ammonium oxidation (S-Anammox) is a novel biological process that involves the oxidation of NH₄⁺ coupled with the reduction of SO₄^2-. This process has been observed under both inorganic and organic conditions; however, the nitrogen removal performance and the specific functional species in these two contexts remain poorly understood. Furthermore, the simultaneous occurrence of coupled sulfate reduction and sulfide oxidation adds complexity to the understanding of nitrogen and sulfur conversions. This study conducted a comparative analysis of the effects of inorganic and organic conditions on S-Anammox. The results demonstrated that the inorganic treatment exhibited a higher NH₄⁺-N removal rate and activity (0.11 kgN/(m³ d) and 1.10 mgN/(gVSS h)) compared to the organic treatment (0.04 kgN/(m³ d) and 0.34 mgN/(gVSS h)). The sulfur cycle was particularly evident in the inorganic treatment, which showed a limited sulfate reduction rate of 0.02 kgS/(m³ d). More sulfate was removed in the organic treatment, resulting in an increase in the retention of sulfur (from 0.8% to 6.0%) in the sludge. qPCR analysis revealed that organic matter inhibited the abundances of key genes involved in ammonia oxidation (amoA and hao) and sulfide oxidation (soxB). Inorganic conditions are more favorable for S-Anammox. Sulfate reducing bacteria such as Desulfococcus multivovans and unidentified species, along with sulfide oxidizing bacteria including Comamonas flocculans, Candidatus Desulfobacillus denitrificans, and Thiobacillus denitrificans, were identified as contributors to the enhancement of the sulfur cycle under inorganic conditions.