End-of-life membrane modification inside spiral-wound modules using layer-by-layer coating with polyelectrolytes

Abstract

Possibility for membrane modification of end-of-life reverse osmosis spiral-wound elements was investigated in this study. End-of-life membrane was successfully cleaned from the membrane fouling and converted to ultrafiltration membrane by oxidation in sodium hypochlorite solution. For the first time, in-situ layer-by-layer coating with polyelectrolytes was performed inside a spiral-wound element. Polyelectrolytes pair used in this study was cationic polyacrylamide and an anionic sodium polyacrylate. Dependence of cationic polyelectrolyte solution viscosity on different temperatures was studied and analyzed with Modular Compact Rheometer. Obtained membrane surface modification was studied by means of flux and rejection properties. Membrane zero sample, from autopsied spiral-wound module, was prepared and compared with the coated membrane. Zeta-potential and Fourier-transform infrared spectroscopy were used to analyze the membrane surface before and after coating. Best results were achieved for the membrane coated with thirteen bilayers, with pure water permeability of 8 L/(m2*h*bar) and magnesium sulfate rejection of 70%. Given results showed the possibility for the layer-by-layer polyelectrolytes assembly inside of the spiral-wound module. Applied technology represents a sustainable way for the reuse of the membranes with expired service life.