Identifying active concentrations of biopolymers for enhancing membrane nanofiltration performance: from bench-scale tests to real production considerations

Abstract

In the last decades, membrane-based nanofiltration (NF) technique has been widely applied for safe and high-quality drinking water production worldwide. NF membrane fouling has become one of the main obstacles in its application due to high operation cost, and thus numerous efforts have been made. However, there is still a large disconnect between academic findings and their applications. Hence, novel approaches for further exploitation and application are required based on feasibility of implementation. In this work, an optimized design of membrane-based NF plants was proposed, inspired by natural biopolymers present in feed water of NF unit. Specifically, we found beneficial functions of biopolymers, including NF membrane fouling alleviation and effluent quality improvement; these advantages could only be "activated" under a certain concentration range of biopolymers (0-1 mg C/L here), and less or more is not acceptable. This indicated that a NF unit is better to follow a microfiltration (MF) (instead of ultrafiltration (UF) which removes biopolymers) process during which natural biopolymers could be remained; also, this approach is suggested to be valid across different seasons when biopolymers' concentrations could be controlled within an "activated" range by mixing MF and UF permeates. Furthermore, three representative reference biopolymers with different, confirmed spatial structures and molecular weight (MW) were used to elucidate the micro-level functions of natural biopolymers on NF membranes, suggesting that cake layer structures shaped by various biopolymers determine the resulting NF performance. Overall, this innovative proposal is expected to be considered and adopted towards more energy-efficient NF technology for drinking water supply.