Potential regulation accelerates element sulfur metabolism in sulfur autotrophic denitrification

Abstract

Sulfur autotrophic denitrification is a feasible option for nitrate removal from wastewater. Element sulfur (So) can be utilized as an electron donor to enhance denitrification processes, with So metabolism playing an important role. The general concern with the use of So as an electron donor is the conversion and transfer of So, since So hardly dissolves in water. The conversion of So and the transfer of intermediates in So-based biofilms was investigated by applying a negative potential in a denitrification reactor with a So-carbon black cathode. The nitrate reduction rate was greatly increased, while nitrite accumulation was limited. When the cathode was prepared with equal volumes of element sulfur and carbon black powder, the nitrogen removal rate could reach 1.03 ± 0.00 g/m2/d. Half-order rates still applied to the reactions with applied potential, indicating that So-based denitrification was the dominant process. Raman analysis and cyclic voltammetry experiments suggested that reduced sulfur species (Sx2−) were generated in a So-based biofilm with a negative potential, their transfer was stimulated, and the sulfur related bacterial community was enhanced. It could be concluded that applying a negative potential improved the conversion and transfer of sulfur species, and thereby promote So-based denitrification process.