Characterization and comparison of microbial communities in sequential sedimentation-biofiltration systems for removal of nutrients in urban rivers

Abstract

The present study described the nutrient removal efficiency of two multi-zone biofilters with different working time, eight vs two years, focusing in metabolic and genetic characteristics of microbial communities. They are known as sequential sedimentation-biofiltration systems (SSBSs) for the removal of nitrogen and phosphorus compounds in urban rivers. Nutrient removal performances for both SSBSs were up to 55% for N-NO2, 46% for N-NO3 and 96% of TP, however, an increase of N-NH4 in the outflow was observed for the eight-year SSBS (Sok-SSBS). Analysis of microbial communities in sediments showed similar metabolic activity for all zones in both SSBSs, suggesting no significant difference according to the working time, but the lowest metabolic activity was observed for geochemical zones, which contained a limestone barrier for the removal of phosphorus. The quantity of key functional genes, involved in nitrogen transformation cycle, showed that denitrifying bacteria (up to 1.16 × 108 copies of nosZ gene g−1) were more abundant than nitrifying bacteria (up to 5.68 × 105 copies of amoA gene g−1) in SSBSs sediments. Maximum abundances of both gene copy numbers were observed in the denitrifying zone presented only in the two-year SSBS (Str-SSBS). The above results suggested that both SSBSs could be recommended as a useful solution to improve water quality in urban areas. However, the implementation of the denitrifying zone, containing brown coal, significantly increased the abundances of denitrifying and nitrifying bacterial communities. In consequence, the efficiency of N-NH4 removal in Str-SSBS could be enhanced compared to Sok-SSBS. Furthermore, microbial metabolic activity in geochemical zones could be strengthened with the application of biopolymers carrying additional carbon substrates, in order to promote biofilm formation in the limestone barrier.