Study of pollutant accumulation characteristics and microbial community impact at three bioretention facilities

In this paper, three bioretention facilities (BT, RG1-A, and RG1-B) were selected for on-site testing and experimental analysis. Of which, BT is a roadside bioretention tank with layered filler, while RG1-A and RG1-B are rain gardens with conventional filler (Bioretention soil media, BSM) and modified filler (BSM+10% Water treatment residuals,WTR), respectively. The effect of pollutant accumulation on the soil microbial community structure in the facilities, and the risk of heavy metal contamination over several years of bioretention facility operation were studied. Results showed that the water quality pollutant load reduction in BT was fluctuating. This is related  to the poor water quality of road stormwater flowing into BT and the facility filler. Because RG1-B uses modified filler, RG1-B was more effective than RG1-A in regulating water quality and quantity; the changes in soil physical and chemical properties in BT, RG1-A, and RG1-B were influenced by external factors. Next, BT was at high risk of heavy metal contamination than other facilities. The microbial community structure of the facility had the following characteristics: at the phylum level, Proteobacteria was the dominant phylum in the bioretention facility, accounting for 29-45%; and at the genus level, Blastocatella was the dominant phylum, and the relative abundance in situ was higher than that in the bioretention facility. The results of the correlation analysis combining filler environmental factors and microbial community structure indicated that SMC was a highly influential factor among the three facilities.