Removal of Pollutants from Urban Surface Runoff by a Straw-Based Composite Bioretention System
Surface runoff pollution has become a significant source of water contamination. This study constructed an integrated composite bioretention system comprising straw, aquatic plant, and biochar zones for purifying urban surface runoff, aiming to meet the standards for reuse as landscaping water. The system's performance in removing conventional pollutants and polycyclic aromatic hydrocarbons (PAHs) was investigated, along with microbial community structure analysis. Results showed removal efficiencies of 81.1% for COD, 98.1% for TN, 79.1% for TP, and 90.3% for TSS, with effluent meeting the 'Water Quality for Scenic and Recreational Use' (GB/T 18921-2019) standard. The system exhibited robust resistance to pollutant and hydraulic loading. The alkali-modified straw zone was the primary pollutant removal region, facilitating physical adsorption and capture of suspended solids, while released carbon sources enhanced total nitrogen removal. This zone exhibited the highest microbial richness, with relative abundances of Proteobacteria and Firmicutes at 54.3% and 21.9%, respectively. The system effectively removed all 16 priority PAHs, reducing effluent toxicity equivalent by 86.5%. The straw zone completely removed four high-molecular-weight PAHs (BaP, DahA, BghiP, IcdP), while aquatic plants and biochar effectively removed medium- and low-molecular-weight PAHs.