Development of polyelectrolyte multilayer membranes to reduce the COD level of electrocoagulation treated high-strength wastewater.

This study focused on developing a membrane-based purification process, coupled with electrocoagulation (EC) as the pretreatment step, to reduce the COD level of an anaerobic digestion effluent. Commercial brackish water reverse osmosis (RO) membranes offer high COD removal but very low water fluxes. In an effort to address this issue, polyelectrolyte multilayer (PEM) membranes were fabricated by the surface modification of loose nanofiltration membranes using layer-by-layer assembly technique. The application of PEM membranes to treat wastewater effluents has not been explored in details. Two polyelectrolyte combinations were tried – the first one consisted of poly (diallyl dimethyl ammonium chloride) and poly (styrene sulfonate) while the second one consisted of poly (allylamine hydrochloride) and poly (acrylic acid). In comparison to commercial RO membranes, these membranes offered significantly higher fluxes, albeit with equivalent COD reduction. The effect of effluent properties like pH and composition, on the performance of these membranes has been discussed. The PEM films were characterized based on properties like thickness and surface charge, which directly affected the separation behavior of the membranes. For the first time, the combination of EC and PEM membranes has been tried out as a simple, energy-efficient two-step process for treating high-strength wastewater. [ABSTRACT FROM AUTHOR]