Advanced treatment of wastewater from an iron and steel enterprise by a constructed wetland/ultrafiltration/reverse osmosis process

To reduce their fresh water consumption, Baosteel Co. Ltd. has attempted to reclaim its mixed treated wastewater. Due to the high conductivity, high iron and manganese concentrations, it was not suitable for reclamation of processes demanding high water quality. In this paper, the feasibility and effectiveness of constructed wetland as pretreatment method were investigated in a constructed wetland/ultrafiltration/reverse osmosis (CW/UF/RO) process. The results show that the iron and manganese concentration and the silt density index in the effluent from the constructed wetland were reduced to 0.05 mg/L, 0.04 mg/L and 4.71, respectively. However, no reduction in conductivity was observed when the hydraulic retention time of the constructed wetland was 1.5 days. The CW/UF/RO process was stable with the recovery rate of 75% and the desalination rate was up to 98%. Compared with the UF/RO process, the operating pressure and backwash frequency decreased from 1.15–1.22 MPa and 8 h, to 0.9–1.2 MPa and 12 h, respectively. After continuous operation for 61 days, there appeared to be no need for chemical cleaning of the reverse osmosis membrane. Analysis showed that there was only slight membrane fouling, which was mainly colloidal blocking caused by refractory organic compounds.