Membrane biofouling mitigation via immobilizing AgNPs@ZIF-8 microcapsules on membrane surface for extractive membrane bioreactor

Abstract

During the extractive membrane bioreactor (EMBR) process, the membrane mass transfer efficient would be significantly reduced due to the biofilm aggregation on the membrane surface. In order to mitigate the membrane biofouling, the microcapsules developed by encapsulating silver nanoparticles (AgNPs) into the zeolitic imidazolate framework-8 (ZIF-8), were immobilized on the membrane surface for the first time. The AgNPs@ZIF-8 microcapsules could ensure the well compatibility between the micromaterials and membrane surface, avoid direct exposure of AgNPs to biomass, as well as slowly release the silver ions on the membrane surface. Compared to the unmodified membrane #M0 (declined to 55% of its initial value) and ZIF-8 modified membrane #M1 (declined to 80% of its initial value), the AgNPs@ZIF-8 microcapsules-coated membrane #M2 displayed the best anti-biofouling performance with a stabilized phenol mass transfer coefficient of 31.04 × 10–7 m/s (96% of its initial value) after 14-days EMBR testing. Its excellent anti-biofouling property should be attributed to the electrostatic repulsion between membrane surface and microorganisms, antibacterial effects from ZIF-8, improved phenol affinity of the membrane, reduced membrane hydrophobicity, stable released silver ions, broad-spectrum bactericidal properties of the silver ions and reactive oxygen species.