Nitrate removal by a sulfur-based autotrophic process: Insights into performance, kinetics behavior and community

Nitrate pollution in water and wastewater has become a significant environmental concern. Presently, thorough research was needed on the sulfur autotrophic denitrification (SADN) process for the removal of nitrate (NO₃^--N) from wastewater characterized by a deficiency in the carbon-to-nitrogen (C/N) ratio. Therefore, this study utilized thiosulfate as an electron donor, to investigate nitrate removal in a sulfur-based autotrophic reactor performance, community, and kinetics behavior. The findings demonstrated that a molar ratio of sulfur-to-nitrogen (S/N) of 2.19 provided enough electron donors to complete denitrification. However, nitrate was selectively reduced, accumulating nitrite in the S/N molar ratio of 1.88. Furthermore, the maximum specific nitrate reduction rate (SNaRR) was 14.50 mg NO₃^--N/g VSS.hr at pH 7 was optimal for denitrification. Denitrification efficiency was limited at pH < 6 or > 8, with SNaRR values of 1.66 and 2.8 mg NO₃^--N/g VSS.hr at pH 5 and 9, respectively. Moreover, the highest denitrification rate was achieved under anoxic conditions with dissolved oxygen (DO) was 0 mg/L. The denitrification effect was severely inhibited under microaerobic (DO = 1 mg/L) and aerobic (DO = 3 mg/L) conditions. Also, the accumulation of nitrite served as an appropriate indicator of the sulfur autotrophic denitrification (SADN).