Strategy for treating highly bio-polluted wastewater using fluidized MOF/GAC composites in an ultrafiltration system

Ultrafiltration (UF) is widely used for microbial removal from water and wastewater. However, its inability to inactivate retained microorganisms often leads to severe membrane biofouling when treating highly bio-polluted wastewater. To overcome this limitation, this study developed MOFs/GAC composites by chemically immobilizing antimicrobial metal-organic frameworks (MOFs) onto granular activated carbon (GAC) particles and subsequently integrating the fluidized composites with a UF process for biofouling control. Comprehensive characterizations verified the successful synthesis of Ag-MOFs, Cu-MOFs and Fe-MOFs and their chemical immobilization on GAC particles via polydopamine coating and mercapto-poly(ethylene glycol)-carboxylic acid linkage. Operational results demonstrated that such MOFs/GAC-UF systems significantly reduced biofouling formation through synergistic physical scouring and MOF-mediated chemical biocidal action. The fluidized Ag-MOFs/GAC composites exhibited optimal sterilization efficacy of 92.2%-95.7% against suspended E. coli , S. aureus and M. aeruginosa even at a high microbial concentration of 10⁸ CFU/mL. As the ion reservoir, three MOFs sustainably released antimicrobial ions in the forms of Ag⁺, Cu²⁺ and Fe³⁺ into wastewater, which could be partially retained by biofilm, resulting in the massive cell death in suspension and on membrane surfaces. Meanwhile, the amounts of ions detected in the effluent remained substantially below drinking water standards, indicating a low risk of metal contamination under the investigated conditions. Consequently, this novel strategy addresses the current challenge of treating highly bio-polluted wastewaters, where the microbial concentrations at least 100 times higher than those found in conventional waters or wastewaters.