Performance and by-product generation in sulfur-siderite/limestone autotrophic denitrification systems: Enhancing nitrogen removal efficiency and operational insights

Sulfur autotrophic denitrification technology is a promising nitrogen removing process and is suitable for the tail water of sewage treatment plants with easy biodegradation and low C/N ratio. Nitrogen removal efficiency and along-path variation of related product concentrations in the sulfur-siderite autotrophic denitrification (SSAD) and sulfur-limestone autotrophic denitrification (SLAD) systems were comprehensively investigated in this work. The optimal denitrification conditions for SSAD and SLAD systems were pH of 7, HRT of 3 h, temperatures of 20-25 degrees C with NO3--N removal rates of more than 99%. Although a greater capacity for alkalinity was provided by limestone than siderite, siderite can also meet the advanced nitrogen removal of SSAD system. A transient accumulation of NO2--N in the SLAD system eventually decreased to 0.02 mg/L, while S2- concentration gradually increased relative to SSAD. It might be due to the fact that Fe2+ promoted the nitrogen removal efficiency of SSAD system and further reduced the content of intermediates in the nitrogen removal process. The results obtained may provide the scientific basis and technical countermeasures for the application of sulfur autotrophic denitrification in actual low-C/N wastewater.