Rapid Treatment of Urban Initial Rainwater Runoff by A/O–Magnetic Flocculation Combined Process

The acceleration of urbanization with the increased proportion of impermeable surfaces has posed significant challenges for old urban drainage systems, particularly during periods of heavy rainfall. Urban initial rainwater runoff pollution, containing a considerable quantity of pollutants, has severely contaminated the urban water environment. The present study presented an A/O–magnetic flocculation (A/O-MF) process for the rapid treatment of urban initial rainwater runoff pollution to realize the simultaneous removal of NH4+-N, TN, COD, TP, and SSs. The optimal operation parameters were obtained by the single-factor and orthogonal methods. The results showed that the optimal operation duration of the A/O process was 10 min for the anoxic process and 60 min for the aerobic process. The optimal dosages of the flocculants were 105 mg/L for PAC, 3 mg/L for PAM, and 30 mg/L for Fe3O4 with a sedimentation time of 2 min. To treat the actual runoff rainwater, the A/O-MF process improved the removal efficiencies of TP, SSs, NH4+-N, and COD compared with the single A/O process, with efficiencies of 99.5%, 93.3%, 99.7%, and 91.3%, respectively. The total operation duration was only 74 min, which could enable the rapid and efficient treatment of urban runoff rainwater.