In-situ graft-polymerization modification of commercial ultrafiltration membranes for long-term fouling resistance in a pilot-scale membrane bioreactor

Despite significant advances in the design of submerged membrane bioreactors for wastewater treatment, membrane organic- and biofouling remain major obstacles to effective operation, decreasing process performance and membrane lifetime. In this work, we report an improved methodology to minimize fouling in commercial polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes using redox-initiated copolymer grafting. To effectively bind a copolymer that possesses oppositely charged groups to the surface, we modified the membranes during filtration using positively charged [2-(methacryloyloxy)ethyl]-tri-methylammonium (MOETMA) and negatively charged 3-sulphopropyl methacrylate (SPM) monomers, which provide the polyampholyte coating. The binding of the grafted copolymer was verified using Fourier-transform infrared spectroscopy and contact angle measurements. Bench-scale dynamic fouling experiments were employed to optimize the modification time and verify the effectiveness of the modification in mitigating fouling from soluble microbial products and extracellular polymeric substances extracted from municipal wastewater. After demonstrating fouling resistance at the bench scale, membrane fibers were tested in a custom-made membrane bioreactor treating municipal wastewater. During 22 days of testing, fouling was consistently reduced in the case of modified membranes due to the presence of the polyampholyte copolymer barrier that hinders foulant adsorption. At the end of the testing period, the flux of modified fibers was 123% higher than that of the PVDF control. Overall, this work demonstrates a facile and effective modification technique to reduce fouling in ultrafiltration with proven performance during long-term treatment of municipal wastewater.