Impact of temperature switching on nitrogen removal and effluent S/N ratio via sulfur autotrophic denitrification

Seasonal temperature alternation severely affects the biological denitrification of high nitrogen concentrations in industrial wastewater. This study used sulfur-based filled particles for the sulfur autotrophic denitrification technique, and evaluated the performance of the sulfur autotrophic denitrification (SAD) reactor for the removal of high concentrations of NO₃^--N by simulating seasonal shifts and switching between 10℃ and 30℃ for 275 days. By precisely adjusting influent nitrate-nitrogen and Hydraulic Retention Times (HRTs), studies revealed enhanced nitrogen removal loading (NRL) at 30℃. Growth of sulfur autotrophs and electron transfer were inhibited at 10℃, and metabolites and biological residues supplied organic matter to heterotrophic denitrifying bacteria, resulting in lower sulfate production and significantly lower S/N ratios than at 30℃. Response surface optimization indicated optimal conditions: 83 % denitrification rate at 27.94℃, 18.7 h HRT, and 135.79 mg/L influent concentration, aligning closely with experimental findings. Thiobacillus and Thermomonas were more abundant at 30℃. And higher correlation of microorganisms between the two samples at high and low temperatures under high-concentration influent conditions. Additionally, the application of the SAD system is economically feasible because its raw materials are low-cost sulfur-based materials. This study aims to demonstrate the advantages of temperature in sulfur autotrophic denitrification, enhance the understanding of its mechanism, and provide a basis for wastewater treatment applications.