Effect of Mn²⁺ on RO membrane organic fouling: Insights into the complexation and interfacial interaction

RO process is commonly used to treat and reuse manganese-containing industrial wastewater. Nevertheless, even after undergoing multi-stage treatment, the secondary biochemical effluent still exhibits a high concentration of Mn²⁺ coupled with organics entering the RO system, leading to membrane fouling. In this work, we systematically analyze the RO membrane organic fouling processes and mechanisms, considering the coexistence of Mn²⁺ with humic acid (HA), sodium alginate (SA), bovine serum albumin (BSA) and their mixtures (HBS). The impact of Mn²⁺ on membrane fouling was HBS > SA > HA > BSA, controlling polysaccharide pollutant concentrations should be a priority for mitigating membrane fouling. In the presence of Mn²⁺ with HA, SA, or HBS, membrane fouling is primarily attributed to the complexation of organics and Mn²⁺ and the facilitation of interfacial interaction energy. RO membrane BSA fouling was not directly affected by Mn²⁺, the addition of Mn²⁺ induced a salting-out effect, leading to the deposition of BSA in a single molecular on the membrane. Simultaneously, adhesion energy hinders the deposition of BSA on the membrane, resulting in milder membrane fouling. This study provided the theoretical basis and suggestions for RO membrane organic fouling control in the presence of Mn²⁺.