Removal of Organic and Nitrogenous Contaminants of Wastewater By Polyelectrolyte Multilayer Membranes

The alarming depletion of fresh water resources all over the world has led to widespread water shortages. As the gap between demand and supply is growing with the increase in population the occurrence of several water-borne diseases is also on the rise especially in the developing countries. Designing cost-effective water purification technologies to recycle and reuse wastewater is therefore the need of the hour. Reduction in the chemical oxygen demand (COD) and total Nitrogen (TN) values of wastewater are two very important parameters for wastewater purification. Reverse osmosis (RO) which is one of the most efficient membrane-based separation processes offers very high reduction of these parameters. However the RO membranes inherently offer very low water fluxes across them making the process energy-intensive. Nanofiltration (NF) membranes on the other hand allow higher water fluxes but lower solute rejections as compared to RO membranes. In our work we modify the surfaces of existing NF membranes using the Layer-by-layer (LbL) assembly technique in order to render them higher perm-selectivity as compared to commercial RO membranes. LbL is as aqueous-based process involving the sequential deposition of alternately charged polyelectrolytes on a substrate leading to the formation of polyelectrolyte multilayer (PEM) films. The tremendous versatility associated with this method in terms of its design parameters helps optimizing the membrane performance with extreme precision. The PEM membranes owing to their high perm-selectivity can potentially replace the traditional RO membranes. The wastewater sample under consideration is the effluent from an anaerobic digestion (AD) process which was further treated in an electrocoagulation (EC) unit prior to being used as the feed for the membrane processes. The membranes are tested in a stirred dead end membrane module and the COD and TN quantifications are done using commercial HACH kits.