Integration of nanofiltration for the sustainable management of reverse osmosis brines

Abstract

The aim of this work is to develop an integrated process for the sustainable management of reverse osmosis brines generated in desalination plants. The core of the proposed process is the bipolar membrane electrodialysis (BMED), which has proved to be a technically feasible option for the conversion of RO desalination brines into HCl and NaOH. However, the overall process should also integrate the brine purification treatment. Precipitation with NaOH, using the reactant produced in BMED, would be the most suitable option for hardness removal. On the other hand, the presence of sulphate affects negatively the quality of the hydrochloric acid product and the current efficiency of BMED. Therefore, in this work nanofiltration (NF) has been applied in order to retain sulphate. This work reports the mathematical model that describes the transport of binary aqueous solutions of chloride and sulphate anions through the NF270 nanofiltration membrane. The relevance and the difficulty of the task lie on the high concentrations of both anions, as it occurs in the RO brines generated in the desalination of brackish water, and the variety of valence charge of the species, monovalent chloride and divalent sulphate, that introduces significant differences in the interaction of both anions with the charged membrane surface.