Potential regulation accelerates element sulfur metabolism in sulfur autotrophic denitrification

Sulfur autotrophic denitrification is a feasible option for nitrate removal from wastewater. Element sulfur (S degrees) can be utilized as an electron donor to enhance denitrification processes, with S degrees metabolism playing an important role. The general concern with the use of S degrees as an electron donor is the conversion and transfer of S degrees, since S degrees hardly dissolves in water. The conversion of S degrees and the transfer of intermediates in S degrees-based biofilms was investigated by applying a negative potential in a denitrification reactor with a S degrees-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/m(2)/d. Half-order rates still applied to the reactions with applied potential, indicating that S degrees-based denitrification was the dominant process. Raman analysis and cyclic voltammetry experiments suggested that reduced sulfur species (S-x(2-)) were generated in a S degrees-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 S degrees-based denitrification process. (C) 2019 Published by Elsevier Ltd.