Simultaneous removal of nitrite and organics in a biofilm-enhanced high-salt wastewater treatment system via mixotrophic denitrification coupled with sulfate reduction

Abstract

The reduction of sulfate to sulfide was seldom considered for high-salt wastewater treatment, although sulfide could supply electron donors to remove nitrite. The sulfate reduction, heterotrophic denitrification and autotrophic denitrification were integrated in one biofilm-enhanced high-salt wastewater treatment system and the sulfate reduction was used as an intermediate reaction. Both the reactor performances and the spatial distribution of the bacterial communities were studied. The metabolic pathways of carbon, nitrogen and sulfur were also discussed based on functional genes analysis. The removal efficiencies of nitrite and organics reached 100%, attributed to the stable and functional bacterial community. Desulfobacter, Sulfurimonas, Fastidiosipila and Pseudomonas were the dominant functional bacteria in the biofilm. The abundance and diversity of bacteria decreased with the increase of water depth because the different spatial concentrations of the substrates brought the various strength of each bio-reaction. Sulfate reduction was achieved through the assimilation pathway by various sulfate reduction genes. The oxidation of sulfide and reduction of nitrite were achieved through the autotrophic/heterotrophic denitrification pathways with functional genes. The seawater’s high salinity promoted the synergistic effect of sulfate reducing bacteria and desulfurization-denitrification bacteria, which helped the efficient operation of this biofilm-enhanced treatment system.