A hybrid ion exchange-nanofiltration (HIX-NF) process for energy efficient desalination of brackish/seawater

摘要

This study reports a new hybrid ion exchange-nanofiltration (HIX-NF) process for desalinationnof sea and brackish water that can attain significant energy economy over the conventionalnmembrane-based pressure driven processes. In this hybrid process, an ion exchange stepnconverts monovalent chloride ions of saline water to divalent sulfate ions and the resultingnsolution, having a reduced osmotic pressure than the feed, is desalinated using a nanofiltrationn(NF) membrane. The sulfate rich reject stream from the NF process is used to regenerate thenanion exchanger. Results validate that NF membranes can desalinate sodium sulfate solution atna much lower transmembrane pressure compared to RO membranes as well as yield a highernpermeate flux. The sulfate-chloride selectivity of the anion exchangers plays important role innsustainability of the process. Laboratory studies have revealed that a single type of anionnexchanger cannot sustain the process for saline water with different salt concentrations.nHowever, anion exchangers with different sizes of amine functional groups (e.g. quaternary-,ntertiary-, secondary- and primary amine) hold the promise that the process can be tailored tonachieve sustainability. Laboratory studies have validated the basic premise of the hybrid processnincluding greater than two times less energy requirement than RO process for the same feednwater and same permeate recovery condition.