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

Abstract

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 (S0chem)) 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 S0chem, 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.