Mixotrophic denitrification using pyrite and biodegradable polymer composite as electron donors

Abstract

The denitrification performance of a novel mixotrophic system using pyrite (FeS2) and biodegradable polymer composite (PLA/PHBV/rice hulls, PPRH) as electron donors was investigated. After 12-day operation, the average nitrate removal rate (16.3–40.6 mg-N/L/d) in the mixotrophic system was 37% higher than the combined rate in the single heterotrophic and autotrophic system. The XPS analysis identified the formation of SO42−, S2− and Fe(Ш) on the pyrite surface during mixotrophic operation. The predicted microbial function analysis by PICRUSt2 revealed that the genes involved in S-oxidation, denitrification and carbon fixation were notably enriched in the mixotrophic system, indicating the increasing contribution of autotrophic S-oxidizing denitrification to total nitrate removal. Moreover, network analysis suggested the synergistic interactions among heterotrophic denitrifiers, S-oxidizing denitrifiers, sulfate reducers, Fe(II)-oxidizing denitrifiers and Fe(Ш) reducers. This study provides novel insights into the molecular mechanism of C, N, S and Fe cycle in the pyrite/PPRH based mixotrophic denitrification system.