Insights into enhanced pollutant removal from road runoff by functional microorganisms in a field-scale bioretention facility

Bioretention facilities (BRFs) can effectively control runoff pollution, but the mechanisms underlying the use of functional microorganisms to remove road runoff pollutants in authentic BRFs remain unclear. In this study, a field-scale BRF was operated continuously for 1 year: the average removal of suspended solids (SS) and ammonia-nitrogen (NH3-N) from road runoff reached 94.2 % and 88.4 %, respectively, and the chemical oxygen demand (COD) was 77.7 %. By using high-throughput sequencing technology and functional prediction, the microbial community structure of the soil samples was analyzed. At the phylum level, the functional bacteria performing nitrification were detected as Proteobacteria, the dominant phylum (30.6–52.6 %). At the genus level, Nitrosomonas (0.7–2.5 %) and Nitrospira, were primarily responsible for nitrification. Chemical heterotrophic bacteria that perform mineralization, such as Bacteroidota (1.7–5.0 %), were also detected. The cover layer of the facility and the loose porous media layer with a high ion-exchange capacity effectively intercepted and adsorbed pollutants, such as SS and NH3-N, and reduced COD. The runoff pollutants were further removed by functional microorganisms that performed nitrification, denitrification, and mineralization functions, which enhanced the reduction of NH3-N and COD levels. This study provides a theoretical basis and practical experience for the application of biological retention facilities.