Pilot-scale constructed wetlands for swine wastewater treatment: Microbial community analysis in bacterioplankton and epiphyton and options for resource recovery

In this study, the abundance and structure of bacterial and denitrifying functional genes of epiphyton and bacterioplankton in pilot-scale surface flow constructed wetlands treating different ammonium nitrogen concentrations (similar to 0.2, 40, 170, and 230 mg/L) of swine wastewater were investigated by quantitative PCR. The gene abundance of denitrifiers in epiphyton outnumbered the gene abundance of denitrifiers in bacterioplankton (P< 0.01), e.g., nirK gene abundance: 1.6-4.5 x 10(7) vs 0.23-1.5 x 10(4) copies/ng DNA. A nitrogen concentration-dependent microbial community structure was observed for epiphyton and bacterioplankton. Proteobacteria, Bacteroidetes, and Actinobacteria dominated at the phylum level in both epiphyton and bacterioplankton. The nirS gene abundance in both niches was negatively related to the dissolved oxygen and redox potential of wastewater, but it was positively related with the Bacteroidetes and Flavobacterium abundance. The results indicated that microbial community structure and abundance are distinct between epiphyton and bacterioplankton. This study also demonstrate that epiphytic biofilms play an important role in denitrification during the treatment of swine wastewater in constructed wetlands. Finally, since swine wastewater serves as an excellent source for nutrients, possible technological options including periphyton techniques for resource recovery from wastewater and future research prospective have been suggested.