Improved Performance of Sulfur-Driven Autotrophic Denitrification Process by Regulating Sulfur-Based Electron Donors

Sulfur-driven autotrophic denitrification (SADN) has demonstrated efficacy in nitrate (NO3-) removal from the aquatic environment. However, the insolubility of elemental sulfur (S0) (maximum 5 mu g/L at 25 degrees C) limited the NO3- removal rate. In this study, we investigated the performance of a laboratory-scale S0-packed bed reactor (S0-PBR) under various volumetric NO3- loading rates. By filling with smaller S0 particles (0.5-1 mm) and introducing chemical sulfide (30-50 mg S2--S/L), a high NO3- removal rate (1.44 kg NO3--N/(m3 center dot d)) was achieved, which was substantially higher than previously reported values in SADN systems. The analysis of the average specific NO3- removal rates and the half-order kinetic constants jointly confirmed that the denitrification performance was significantly enhanced by decreasing the S0 particle sizes from 10-12 mm to 1-2 mm. The smaller S0 particles with a larger specific surface area improved the mass-transfer efficiency. Dosing chemical S2- (20 mg S2--S/L) to trigger the abiotic polysulfuration process increased the specific NO3- removal rate from 0.366 to 0.557 g NO3--N/g VSS/h and decreased the portion of removed NO3--N in the form of nitrous oxide (N2O-N) from 1.6% to 0.7% compared to the S2--free group.