Removal efficiency and synergistic mechanism of pollutants by bioretention systems with modified media

Abstract

Aiming at the problems of insufficient nitrogen and carbon removal capacity and vulnerability to hydraulic impact of traditional bioretention system in the process of surface runoff infiltration recharge and in-situ purification of underground reservoirs, an indoor simulated bioretention column was constructed in this paper. With pure fine sand as the control, a single modified group of vermiculite, green zeolite, biochar and sponge iron with a content of 5% and a composite modified group of ‘2.5% biochar + 2.5% sponge iron’ were set up. The dynamic removal characteristics of ammonia nitrogen (NH3-N) and chemical oxygen demand (COD) in each system were analyzed under three simulated rainfall intensities of low, medium and high. The results showed that the removal rate of NH3-N in each system remained above 95%, while the pure inorganic mineral group had poor impact resistance due to the dependence on reversible ion exchange, and the zeolite group had an outlier value of close to 0.8 mg/L in the fluctuation of effluent. In terms of COD removal, the median effluent value of the carbon-iron composite group was stable at 0.6-1.1 mg/L, and the removal rate exceeded 70% under high load. The removal rate of single carbon/iron modified group can reach more than 65% under high load, while that of vermiculite group is less than 25% under low load. The highest effluent of pure sand control group even exceeds 5.0 mg/L, and serious penetration occurs. The research results can provide reference for the engineering utilization of modified filler bioretention system.