Membrane deflections for chemical-free cleaning in desalination
Foo, Zi Hao
Date of Issue2018
School of Mechanical and Aerospace Engineering
Massachusetts Institute of Technology
Population growth triggered by the rapid industrialisation of developing countries, coupled with the adverse effects of global climate change, have exacerbated the problem of water scarcity. Membrane-based filtration like reverse osmosis has proven effective in rejecting contaminants from waste and seawater, allowing for an artificial augmentation of the supply of clean potable water. While energy-efficient and widely adopted presently, the performance of these membranes is limited by the accumulation of foulants on the membrane surface, leading to decreased permeate water production and water quality, while increasing the pumping power requirements due to decreased membrane permeability. Unlike the conventional chemical cleaning technology, the present study aimed to introduce and evaluate the viability of utilising membrane deflections as a physical fouling mitigation technique. Experiments were conducted using both a laboratory coupon-scale membrane and a commercial reverse osmosis membrane, while membrane deflections were induced through the periodic pressurisation of the permeate channel for both setups. Experimental findings indicate that permeate pressurisation was successful in deflecting the membrane, leading to a delamination of the organic film, which was deposited on the membrane surface when intentionally fouled with sodium alginate, a ubiquitous organic foulant. In-situ visualisation of the fouling and cleaning procedures revealed the mechanism of foulant removal, where membrane deflections led to the splicing and chopping of the organic film by the feed spacers, which was subsequently sheared off by the cross-flow. The effectiveness of deflection-induced cleaning was also demonstrated on an actual, commercially-available reverse osmosis membrane. Lastly, the performance of the proposed technique was also juxtaposed with that of the conventional chemical method and the swelling-induced buckling of foulant films, where experimental studies further corroborated the superiority of membrane deflections, when system downtime and overall flux recoveries were evaluated.
Final Year Project (FYP)
Nanyang Technological University