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

Abstract

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 μg/L at 25 °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·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.