Sulfur transformation in sulfur autotrophic denitrification using thiosulfate as electron donor.

Thiosulfate is frequently used as an energy source and electron donor in autotrophic denitrification (AD) for removing nitrate from wastewater. However, transforming pathways of SO in this process is unclear. Herein, the aim of this study is to explore possible transforming pathways of sulfur compounds in thiosulfate-based AD process. After measuring the variation of NO, NO, and various sulfur compounds such as S, SO, SO, acid volatile sulfide (AVS), and S in the presence and absence of SO, the variation process of SO and the contribution of various sulfur compounds were analyzed. The results indicated that S, AVS, and S were the intermediate products when SO was applied as an electron donor. All SO, S, AVS, and S could act as electron donors in the nitrate removal process with the final products of SO. The utilization priority of these four sulfur sources was presumed in the following order: S > SO > AVS ≈ S. Furthermore, sulfur transformation and balance in nitrate removal process was also investigated. This suggests the transforming pathways of sulfur compounds in denitrification process. Nitrogen removal and sulfur conversion process are dependent on the presence of microorganisms in the sludge.