Zwitterionic and anionic ultrafiltration membrane modification for efficient, fouling-resistant microalgae harvesting

Membrane surface modification is a promising strategy for fouling mitigation in membrane-based microalgae filtration, primarily by limiting the interactions between the membrane surface and the foulant particles. This study investigated the effectiveness of modified membranes in filtering Chlorella sp. MUR 269. First, three polyethersulfone membranes with varying pore sizes were evaluated to determine the influence of pore size on filtration performance and fouling behavior. The ultrafiltration membrane that exhibited the best performance was subsequently modified using two functional monomers: the zwitterionic [2-(methacryloyloxy)ethyl]dimethyl (3-sulfopropyl) ammonium hydroxide and the negatively charged mono-2-(methacryloyloxy)ethyl succinate (MMS). The filtration performance and fouling resistance of the modified membranes were then evaluated over a 4-h filtration period. MMS modification enhanced membrane hydrophilicity and surface electronegativity, which resulted in consistently higher permeate flux than the other membranes. However, the MMS-modified membranes exhibited high irreversible fouling (∼37%) and a relatively low flux recovery rate (48%) after 30 min of physical cleaning. In contrast, zwitterionic modification significantly enhanced surface hydration, as evidenced by a low contact angle (29°), and exhibited superior antifouling behavior within the scope of the present study, with low irreversible fouling (∼10%) and a high flux recovery rate (80%). These findings underscore the importance of membrane surface modification in reducing fouling during microalgae filtration and position zwitterions as effective antifouling agents for membrane surface enhancement. Further studies incorporating controlled grafting layer thickness are recommended to clarify how surface chemistry-driven hydration and electrostatic interactions influence microalgal fouling control, alongside with long-term operation and repeated filtration-cleaning cycles to evaluate the durability and sustained performance of the modified membranes. • Antifouling performances of zwitterionic- and MMS-modified membranes against Chlorella sp. were compared. • MMS modification increased electrostatic repulsion against microalgae. • Zwitterionic modification improved membrane hydrophilicity, which ultimately reduced the contact angle from 69° to 29°. • MMS-modified membranes demonstrated high flux and high irreversible fouling, and low FRR. • Zwitterionic-modified membranes exhibited low irreversible fouling (∼10%) and high FRR (∼80%).