Effects of Hydraulic Residence Time, NO3− and NO2− on Sulfate-Reducing Anaerobic Ammonium Oxidation Reaction

The sulfate-reducing anaerobic ammonia oxidation (SRAO) reaction, as a biochemical reaction, is influenced by many factors. Different factors have different removal effects and change the acting bacterial species. In this experiment, we investigated the effects of hydraulic residence time (HRT), organic matter concentration, NO₃⁻, NO₂⁻ and N/S on the SRAO reaction. The influent ammonia and sulfate concentrations were maintained at about 120 mg/L and 250 mg/L, respectively, during the experiment. The highest removal rates of 98.5% and 52.4% were achieved at HRT of 48 h. When HRT was 24 h, the removal rates of both decreased, but the highest removal loads of 0.092 kgN/m³·d and 0.168 kgS/m³·d were achieved, respectively. As the concentration of influent organic matter increased, the activity of SRAO strains decreased and the sulfate removal rate increased, suggesting that the functional bacteria strains were gradually transformed into desulfurizing bacteria. Small additions of NO₃⁻ (30 mg/L) and NO₂⁻ (40 mg/L) during the experimental process could promote the reaction, but too high a concentration would affect the removal of ammonia nitrogen and sulfate. In the SRAO system, controlling the concentration of influent substrate (in the case of low concentration) and N/S in the influent water (N/S = 2) can improve the efficiency of the interconversion of nitrogen and sulfur and reduce the generation of other by-products.