Reducing fl ux decline and fouling of direct contact membrane distillation by utilizing thermal brine from MSF desalination plant

Fouling and scaling is one of the major challenges in membrane distillation process. This study investigates the utilizing of thermal rejected brine produced from multi-stage flash distillation (MSF) to minimize fouling and scaling on membranes in direct contact membrane distillation (DCMD) settings. The effect of operating parameters on permeate flux and the extent of scaling during long time operation was considered and compared when real seawater and reject thermal brine were used. The deposit morphology of scaling was observed using different analytical methods, including scanning electron microscopy and contact angle measurement. Thermal brine showed enhanced performance in terms of flux and scaling compared to seawater. It was found that flux is reduced by 8% compared to 12–20% when the feed to the DCMD was brine was used as compared to seawater. In addition, thermal brine feed showed better anti-fouling behavior compared to the fresh seawater which contains different organic and inorganic contaminants. Furthermore, utilizing waste heat contained in the thermal brine to raise the temperature of the feed was advantageous in increasing the energy efficiency of DCMD process. © 2015 Elsevier B.V. All rights reserved.

Fouling in membrane and specially membrane distillation leads to decline of flux, increase in power consumption, increase of membrane area requirement, change in membrane hydrophobicity and decrease in membrane lifespan. Throughout this study, thermal brine which has been treated in pre-treatment stage at the MSF desalination plant and rejected to sea is used as a feed to DCMD. Usage of thermal brine in comparison to fresh seawater has few advantages such as higher flux, lower flux decline due to fouling, less fouling, less temperature requirement to upgrade the feed temperature, and higher water production from DCMD using the thermal brine which was considered a waste and dumped to the sea. Careful selection of feed and permeate temperature and optimization will reduce chances of wetting and fouling and enhance energy efficiency of DCMD. Acknowledgments The authors would like to express their gratitude to Qatar University and ConocoPhillips GWSC for their financial support of this work under grants QUST-CENG Fall 12/13-22 and QUEX-CWT-11/12-5 respectively.