Effects of polyurethane medium pore size on operation and microbial community of denitrification biofilters

Abstract

[Objective] The denitrification performance and microbial mechanisms of polyurethane(PU) media with different pore sizes in denitrification biofilters(DNBFs) are investigated to clarify the relationship between medium pore size and operating parameters, to reveal the regulatory effects of pore size on biofilm characteristics and nitrogen metabolism functional genes, thereby providing technical support for groundwater nitrate pollution control.[Methods] Three DNBFs were constructed using 15 ppi(large pore), 30 ppi(medium pore), and 40 ppi(small pore) PU media. The empty bed hydraulic retention time(EBHRT) was set to 3, 2, 1.5, and 1 h. The nitrate nitrogen(NO^-₃-N) removal rate and volumetric denitrification rate(R_vd) were monitored. The biomass on the medium surface and the content and composition of extracellular polymeric substances(EPS) were determined. The microbial community structure was analyzed via high-throughput sequencing, and the abundance of nitrogen metabolism functional genes(nirKS, norBC, nosZ) was predicted using PICRUSt2.[Results] At EBHRT=1.5 h, the DNBF with 30 ppi PU medium achieved a higher NO^-₃-N removal rate(93.15%) and R_vd(0.89 kg N·m^-3·d^-1), outperforming those with the 40 ppi(0.83 kg N·m^-3·d^-1) and 15 ppi(0.75 kg N·m^-3·d^-1) media. The biomass on this medium surface was 93.6 mg·cm^-3, and the extracellular polymeric substances(EPS) production was 49.61 mg·g^-1, both of which were higher than those of the other two media. Microbial community analysis showed that the 30 ppi medium enriched a higher relative abundance of the phylum Proteobacteria(63.93%) and denitrifying bacterial groups(e.g., Simplicispira: 15.87%; Cloacibacterium: 14.24%). PICRUSt2-based prediction of nitrogen function further revealed that the abundance of denitrification genes(nirKS, norBC, nosZ) in the 30 ppi medium was 1.6 times and 1.5 times higher than that of the 15 ppi and 40 ppi media, respectively.[Conclusion] The 30 ppi PU significantly improves the denitrification efficiency of DNBFs by increasing biomass and EPS production, enriching denitrifying functional bacterial groups, and enhancing the abundance of key genes. These findings provide reliable support for constructing efficient and stable groundwater nitrate removal systems, and also provide a theoretical basis and technical reference for promoting economically feasible denitrification processes in industrial and municipal wastewater treatment.

Keywords

PU media / pore size / denitrification biofilter / denitrification / biomass / EPS / microbial community / nitrogen metabolism