Enhanced anti-wetted PVDF membrane for pulping RO brine treatment by vacuum membrane distillation

Abstract

Large amounts of lignin, hemicellulose, organic matter and inorganic salts are present in pulping and papermaking wastewater. Therefore, the treatment and discharge of pulping wastewater are important issues. We have designed and developed the world's first zero liquid discharge (ZLD) system for it based on pretreatment-membrane-evaporative crystallization integrated technologies. However, for the treatment of high salt reverse osmosis (RO) brine, there are still challenges that need to be addressed. In this work, the feasibility of using a membrane distillation crystallization (MDC) process to treat high saline RO brine was investigated. Two different coating materials, Hyflon AD 40H and perfluoropolyether (PFPE), were applied to improve the membrane surface hydrophobicity for stable and efficient performance. After modification, the water contact angle was up to 138.4o and 157.7o for Hyflon/polyvinylidene fluoride (PVDF) and PFPE/PVDF composite membranes, respectively. Moreover, the PFPE/PVDF membrane showed a higher repellency toward RO brine, which is better for the following MDC treatment. During the MDC progress using composite PFPE/PVDF membranes, the salt crystals precipitated and gradually accumulated. More importantly, the final NaCl purity can be up to 94%. Therefore, it is hopeful to improve of the existing ZLD system by MDC operation.