Pilot scale experiments and simulation of the purification effects of bioswale on urban road runoff

The purification effects and suitable operation conditions of bio-swale on urban road runoff are investigated through experiment and simulation. Two types of bioswale system were designed:one with semi-permeable substrate, and another with impermeable substarte. Each type consists of 5 bioswales with different typical media. The experimental conditions were selected through multi-level orthogonal test with different influence factors and single-factor analyses. The results show that media combination is the most important factor affecting the overall treatment effect. The bioswales achieved the best purification effect with fly ash mixing sand as the media, and the overall removal rates were 83.12% and 73.18% for the impervious and semipermeable types. The optimal submerged zone height was 150 mm. Multiple regression models among the pollutant (TN, TP) removal rate, discharge rate and operation factors were derived with high determination coefficient (R²) and Nash-Suttcliffe coefficient. The Hydrus-1D model was then used to simulate the TP vertical migration in the bioswale under three influent concentrations. The mean relative errors of effluent concentration between simulated values and measured data were 14.11%, 17.33% and 26.57% respectively, indicating good modeling results.