Role of electrocoagulation-microfiltration in roof rainwater re-utilization: A novel insight into membrane fouling mechanisms through the combination of variations in interfacial properties on the membrane surface and membrane fouling model

This study investigated the impact of hybrid electrocoagulation and ceramic membrane microfiltration (EC-CM) process on the quality of roof rainwater and explored membrane fouling mechanisms from a novel perspective by coupling variations in interfacial properties on the membrane surface and a membrane fouling model. The results showed that the removal efficiencies of SS, COD, NH₃-N, TN, and TP in EC-CM reached 99.5 %, 80.8 %, 27.8 %, 35.1 % and 99.7 %, respectively, fully meeting the re-utilization standards in China. However, EC-CM only slightly improved the normalized flux compared to CM alone, suggesting that EC-CM did not effectively alleviate membrane fouling. To further investigate the membrane fouling mechanisms in EC-CM, comparative studies were conducted using 120 min of CM alone (CM-120), 60 min EC-CM and 60 min CM alone (EC-CM-60 + CM-60), and 120 min of EC-CM (EC-CM-120). The results indicated that EC could sharply aggregate particles into micro flocs and effectively remove fulvic acid-like and humic acid-like substances in organic matter. This process shifted the initial membrane fouling mechanisms from standard and complete blockage in CM alone to complete blockage in EC-CM. During this period, the normalized flux of EC-CM decreased more rapidly than that of CM alone due to larger interfacial energy of micro flocs-CM, leading to more severe chemical irreversible fouling. As the EC process continued, the micro flocs gradually evolved into larger flocs, which accumulated on the membrane surface and formed a cake layer, thus transitioning the fouling mechanism to cake filtration. Due to lower interfacial energy between flocs, EC-CM exhibited less chemical reversible fouling compared to CM alone. Furthermore, larger flocs with lower fractal dimension would form a looser cake layer compared to primary particles, leading to a reduction in physical reversible fouling. Based on the membrane fouling mechanisms mentioned above, the normalized flux was improved to 0.72 by optimizing the operational mode of EC-CM. These findings provide a promising alternative for rainwater re-utilization and offer valuable insights into the membrane fouling mechanisms in EC-CM.