Membrane Pretreatment To Enhance High Brackish Water Desal System Performance

By Ivy Chua, and Richard Woodling, PhD.


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Desalination systems, including thermal, pressure-driven membrane and electrochemical processes, require pretreated feed to ensure their continuous and optimized operations. Common limiting factors in the performance of these systems are scaling and fouling tendencies. In this research, a laboratory scale, low-pressure dual-function membrane module was fabricated to treat high brackish water containing 3,000 parts per million (ppm) total dissolved solids (TDS) mixture of magnesium chloride (MgCl2), calcium chloride (CaCl2), and sodium chloride (NaCl) salts. These membranes consisted of a porous poly(vinylidene difluoride) (PVDF) substrate modified with bilayers of cationic and anionic polyelectrolytes using a dynamic deposition technique. Poly(diallyldimethylammonium chloride) (PDADMAC) and poly(allylamine hydrochloride) (PAH) were used as cationic polyelectrolytes, and poly(sodium styrenesulfonate) (PSS) was used as the anionic polyelectrolyte. Formation of the polyelectrolyte bilayers was confirmed using Attenuated Total Internal Reflection-FTIR (ATR-FTIR) spectroscopy. Morphologies and surface hydrophilicity of the unmodified and the modified hollow-fiber membranes were investigated using Scanning Electron Microscopy (SEM), and contact angle measurement, respectively. Mg2+ rejection of 73% and Ca2+ rejection of 68% were achieved at an operating pressure of 1 bar. The salt water permeability was 10.4 liters per square meters per hour per bar (LMH/bar). Detailed research results will be presented.

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