Improvement of Coagulation and Membrane Filtration Performance in Hybrid Coagulation-UF-RO System for Chemical Mechanical Polishing Wastewater Treatment: Effect of Coagulants

Reverse osmosis (RO) membranes have been widely applied in the advanced treatment of chemical mechanical polishing (CMP) wastewater. However, membrane fouling persists in practical treatment processes. Herein, a hybrid coagulation-ultrafiltration (UF)-RO (CUR) system was used to control the fouling of the RO membrane, and a novel composite coagulant was developed to enhance the coagulation efficacy for CMP wastewater. Compared to traditional processes, the improved Coagulation-UF process exhibited a remarkable capacity, removing 98.62% of total silica and achieving complete turbidity removal in CMP wastewater. Furthermore, the aluminum residual was reduced by 76.47%, and the normalized flux of the RO membrane increased from 0.87 to 0.95. Moreover, the new coagulant achieved remarkable coagulation effectiveness, with silica and turbidity removal rates reaching 97.29% and 99.87%, respectively, while reducing residual aluminum to 15.50%. Notably, dissolved silica in CMP wastewater emerged as the primary contaminant on the surface of the RO membrane. The net sweep was the primary coagulation mechanism of the new coagulant, proving good performance in reducing the burden on both UF and RO membranes. These results exhibit significant implications for designing efficient pretreatment schemes for CMP wastewater and optimizing the longevity of RO membranes in semiconductor plants.