Zwitterionic polymers grafted poly(ether sulfone) hollow fiber membranes and their antifouling behaviors for osmotic power generation

Fouling on pressure retarded osmosis (PRO) membranes must be eliminated to maximize the efficiency of osmotic power generation. This is particularly applicable to PRO membranes due to its nature of fouling when wastewater is fed. To improve this, PRO thin-film composite (TFC) membranes for the first time will be redesigned by incorporating well-defined zwitterionic copolymers of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (DMAPS) or 2-methacryloyloxyethyl phosphorylcholine (MPC) onto the poly(ether sulfone) (PES) hollow fiber membranes. The introduction of 2-methacryloyloxyethyl lipoate (MEL) components into the zwitterionic copolymers provided sufficient grafting sites for the facile decoration of polydopamine (PDA) pretreated PES membranes via Michael addition. The PDMAPS and PMPC grafted membranes were shown to be effective in reducing protein adsorption and bacterial adhesion, in comparison to the pristine PES membranes and PDA pretreated membranes. The pristine TFC-PES membranes are fouled greatly in high pressure PRO tests with concentrated wastewater, resulting in a flux reduction of 61%. In contrast, the TFC-PES membranes grafted by zwitterionic PDMAPS and PMPC copolymers exhibit substantial improvement of flux recovery up to 98% after backwashing and hydraulic pressure impulsion. In summary, the osmotic power generation may be sustained by grafting the PRO membranes with the properly designed zwitterionic polymers.