Water Purification Efficiency and Membrane Fouling Behavior of Ceramic Membrane-Nanofiltration in Treating Water Treatment Plant Production Wastewater

To mitigate the risks associated with production wastewater from water treatment plants, this study evaluated the effectiveness of nanofiltration (NF) and a hybrid ceramic membrane-nanofiltration (CM-NF) process in removing natural organic matter (NOM) and Ca²⁺. A comprehensive analysis of changes in specific flux and fouling resistance of the NF membrane, combined with scanning electron microscopy (SEM) observations, provided deeper insight into membrane fouling behavior. The results show that the CM-NF process achieved average removal rates of 95.60% for DOC, 98.55% for UV₂₅₄, 34.50% for conductivity, and 50.71% for Ca²⁺. These values represent improvements of 4.70%, 1.40%, 16.37%, and 10.36%, respectively, compared to the standalone NF process. Furthermore, CM pretreatment consistently optimized the performance of the nanofiltration system. After continuous operation, the average specific membrane flux of the CM-NF system reached 0.715, 0.67, and 0.61 under varying pollutant concentrations-increases of 10.9%, 19.6%, and 17.3% over the standalone NF system-confirming a significant improvement in permeate flux. Under continuous operation, the average degree of irreversible fouling was markedly reduced across different pollutant concentrations-decreasing from 9.2%, 17.6%, and 23.6% for the standalone NF system to 8.9%, 15.6%, and 10.9% for the CM-NF system, which clearly demonstrates the efficacy of CM pretreatment in controlling irreversible fouling. SEM observations further corroborated that CM pretreatment effectively alleviated fouling on the NF membrane surface. Additionally, higher Ca²⁺ concentrations were found to contribute to reduced membrane fouling and enhance flux performance.