Electron distribution in sulfur-driven autotrophic denitrification under different electron donor and acceptor feeding schemes

Sulfur-driven autotrophic denitrification (SdAD) represents an effective alternative to heterotrophic denitrification process for the treatment of organic carbon deficient or organic carbon free water and wastewater streams. The electron supply by oxidation of sulfur substrates (i.e., total dissolved sulfide (TDS) and chemical elemental sulfur (S-chem(0))) and the electron distribution among nitrogen oxide reductases determines the denitrification rate, reduction and accumulation of intermediates (e.g., nitrite and nitrous oxide). In this study, the electron distribution (supply and consumption) in SdAD process was investigated through a series of batch experiments under electron donor and acceptor non-limiting and limiting feeding conditions. The electron distribution was significantly affected by sulfide loading rate, and the electron competition among nitrogen oxide reductases was intensified with the most electrons flowing towards nitrate reductase (Nar), and the least electrons towards nitrous oxide reductase (Nos) under decreased sulfide loading rate. The intensification of electron competition associated with unbalanced electron supply and consumption rates is more directly responsible for intermediates accumulation in SdAD process. Compared to S-chem(0), TDS was the preferable electron donor as it resulted in the lowest accumulation of denitrifying intermediates in SdAD process. The findings of this study not only improve the understanding of underlying mechanisms of electron distribution and accumulation of denitrifying intermediates in SdAD process, but also form a basis for selection of ideal electron donor and feeding conditions in applying SdAD process for remediation of water, wastewater and gaseous streams containing nitrogen and/or sulfide.

Automated summary

Sulfur-driven autotrophic denitrification (SdAD) is an effective alternative for treating water and wastewater streams with low organic carbon content. The distribution of electrons in the SdAD process is significantly influenced by the rate of sulfide loading, with competition intensifying among nitrogen oxide reductases. Sulfide was found to be a preferable electron donor compared to elemental sulfur, resulting in lower accumulation of denitrifying intermediates.