Experimental Study on Simultaneous Nitrogen and Sulfur Removal in a Sulfur Autotrophic Denitrification Coupled Sulfate Reduction System

Abstract

The application of thiosulfate in large-scale wastewater treatment via the sulfur autotrophic denitrification (SAD) process faces challenges such as high alkalinity consumption, excessive sulfate generation, and chemical instability. To address this, an integrated SAD-SR system was developed by allocating Sulfur Autotrophic Denitrifying Bacteria (SADB) and Sulfate-Reducing Bacteria (SRB) to the upper and lower segments of an Upflow Anaerobic Biofilm (UFAB) reactor, respectively, enabling simultaneous nitrogen and sulfur removal. Optimal operation was achieved at a sulfur-to-nitrogen ratio of 0.5, carbon-to-sulfur ratio of 6, and a reflow ratio of 100%, resulting in maximum NO₃⁻-N removal, significant SO₄²⁻ reduction, and efficient elemental sulfur recovery. At a hydraulic retention time (HRT) of 3 hours and influent NO₃⁻-N concentration of 85 mg/L, the system achieved a nitrate removal efficiency of 90.58%, a load of 0.616 kg/(m³·d), and an effluent SO₄²⁻ concentration of 137.04 mg/L. Continuous pH monitoring confirmed stable acid-base balance due to complementary system interactions. Microbial analysis showed that coupling enhanced Proteobacteria abundance in the SAD section while maintaining Desulfobacterota dominance in the SR section. At the genus level, Thiobacillus abundance in the SAD section slightly declined post-coupling, alongside a reduction in Desulfomicrobium in the SR section. These results demonstrate the SAD-SR system’s efficiency in nitrogen and sulfur removal with potential for large-scale application.

Keywords: Nitrate wastewater, sulfur autotrophic denitrification, coupling, sulfate reduction, simultaneous nitrogen and sulfur removal