In-situ crystallization generated by CEM electrolysis for NF concentrate softening along with the alleviation of ceramic membrane fouling

Abstract Ceramic ultrafiltration (UF) is promising in treating the nanofiltration (NF) concentrate, however, the ceramic UF membrane suffers from severe fouling with inefficient softening. To address such issues, a cation exchange membrane (CEM) electrolysis method was proposed for ceramic UF fouling control by enhancing pH variation, forming the separated-cathode/UF (SCUF) and separated-anode/UF (SAUF), and conventional electrolysis without CEM/UF (control system) was also investigated. The results showed that all electrolysis strategies contributed to UF fouling alleviation; specifically, the separated-cathode outperformed separated-anode. In SCUF process, particles were produced due to the crystallization of calcite and amorphous magnesium hydroxide. Prolonging the electrolysis to 90 min, the inorganic particles accumulated on the membrane surface could be increased to 42.3 gCa/m2 and 11.8 gMg/m2, effectively softening the NF concentrate. Furthermore, the freshly generated particles effectively adsorbed organic foulants, achieving organic removal improvement by 44%. Interestingly, the crystal particles accumulated on the membrane surface, providing a dynamic barrier to avert the migration of organic matter onto the membrane surface. In addition, humic-like substances were transformed into supramolecular organic particles and rejected by the UF membrane under low pH conditions during the SAUF process. These findings would provide practical relevance for the advanced treatment of NF concentrates.