Publication: Surface modification for membrane distillation with thermoresponsive hydrogel and its cleaning efficiency
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Date
2023-01-01
Authors
Lim Wei Jiun
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Abstract
Scarcity of clean water and ways to remedy the situation have always been a problem revolving around researchers. Membrane distillation (MD) as one of the wastewater treatment processes gained much spotlight due to its high theoretical salt rejection, non-pressure driven and low heat requirement. However, some common drawbacks such as fouling and wetting after running the operation for long period of time impeded its widespread use in industries. In this study, thermoresponsive membrane was developed to reduce the fouling tendencies without compromising the membrane structural integrity and flux performances. Poly(N-isopropylacrylamide) (PNIPAM) with silica core nanoparticles were prepared via free radical polymerization and coated on pristine polytetrafluoroethylene (PTFE) membrane via direct coating (DC) and spray coating (SC) at different coating concentrations forming thermoresponsive membrane. The membranes were characterized based on few aspects such as flux, salt rejection, surface structure, contact angle and fouling tendency using bovine serum albumin (BSA) and sodium alginate (SA) as model foulants. It was observed that hydrogel coated membranes (HCM) managed to repel amphiphilic BSA attachment compared to PTFE which can be seen from the less steep flux decline during MD. Recovery efficiencies of membranes were also studied by thermal actuation of PNIPAM which helped repelled foulants by the shrink-swell motion. DC membranes generally exhibited slightly more inferior results than SC membranes in terms of coating uniformity and water flux stabilisation that led to large deviation of results. After evaluating all the data obtained, 0.3% SC membrane was chosen to undergo long hours fouling test and it was found that water flux only dropped by 29.05% and 16.59% for BSA and SA fouling respectively. Then, the membrane achieved 61.82% and 87.03% flux recovery after undergoing thermal cleaning. Surface free energy study (SFE) and wetting behaviour analysis (WBA) on the membrane at different stages (fresh, fouled and cleaned) also provided better understanding on the changes of hydrophilicity/hydrophobicity on the HCM surface. The overall SFE increased when fouled and the effect was especially prominent by BSA foulant as compared to SA. However, it was deemed that membrane coupled with thermoresponsive property improved overall antifouling property compared to pristine PTFE and allowed more convenient cleaning of fouled membrane.