Hybrid electron donor-driven partial denitrification coupled with anammox process for the treatment of high-concentration ammonium nitrate wastewater: Element transformation and microbial community structure

In this study, a mixotrophic nitrogen removal system integrating sulfur-oxidizing autotrophic denitrification, heterotrophic denitrification and anammox was established for the treatment of high-strength ammonium nitrate wastewater. After 170 days of continuous cultivation, the total nitrogen removal rate achieved 1.05 ± 0.05 kg N/(m³·d), with remarkable nitrogen removal efficiency of 88.09 ± 3.97 %, and sulfate production effectively reduced to 37.59 ± 5.44 %. In-situ batch test results not only investigate the element transformation in Mixotrophic Partial Denitrification coupled with Anammox, but also indicated that thiosulfate-driven autotrophic denitrification accounted for 88.20 % of nitrate reduction. Thiobacillus and Thermomonas was identified as the predominant sulfur-oxidizing bacteria. The addition of a low concentration of Chemical Oxygen Demand maintained the relative abundance of heterotrophic denitrification bacteria (27.3–35.6 %). Furthermore, the relative abundance of anammox bacteria including Candidatus_Kuenenia and Candidatus_Brocadia constituted 36.2 %. This research provides a stable and efficient treatment process for high-concentration ammonium nitrate wastewater with low carbon-to‑nitrogen ratios.