Membrane Surface Engineered with Zwitterions for Fouling Mitigation in Membrane Bioreactor: Performance and Mechanism

Zwitterionic surface engineering is an effective strategy to improve membrane antifouling ability. In present study, zwitterions were introduced onto hollow-fiber membrane via a simple flow-through coating method using zwitterionic organosilica material, and then the membrane was incorporated into membrane bioreactor (MBR) to demonstrate improvement in fouling control. Zwitterions endowed membrane with superior fouling resistance in MBR; the critical flux of membrane was improved from 25 LMH to 35 LMH, which signified higher allowable operation flux; the transmembrane pressure (TMP) development was greatly retarded, which resulted in fouling cycle extended by approximately 2 times (from 32 d to 66 d) and less cleaning frequency. Batch fouling experiments with key foulants found that zwitterion-modified membrane had superior resistance to extracellular polymeric substances (EPS) and soluble microbial polymer (SMP) adsorption. In particular, it presented exceptionally high resistance against proteins adsorption. Interfacial free energy analysis revealed that zwitterions substantially altered interfacial interaction between membrane and EPS/SMP, the Lifshitz-vander Waals and Lewis acid-base attractive forces were obviously attenuated. As a result, the energy barrier for foulants attaching on membrane was greatly elevated. Our study provided a deeper insight into the antifouling mechanism of zwitterion-engineered membrane and demonstrated its good potential for improving fouling control in MBR.