Implementation, design and cost assessment of a membrane-based process for selectively enriching desalinated water with divalent seawater ions

Liat Birnhack, Samuel C.N. Tang, Ori Lahav*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The paper describes results from operating a new 3-step membrane-based process targeted at separating Mg2+ from seawater in an inexpensive way, with the purpose of using it to enrich desalinated water with magnesium, with as little as possible Cl and Na+ addition. To this end, seawater undergoes a series of processes aimed at increasing the Mg2+ concentration from ~1350 to ~4000 mg/L through nanofiltration while the monovalent ion concentrations are reduced by a nanofiltration-diananofiltration sequence, in which the diluent is RO produced water from a desalination plant. A dense ultrafiltration (UF) step precedes the nanofiltration-diananofiltration (NF-DiaNF) cycles. In this step sulfate in seawater is rejected better than divalent cations hence the retentate of this step has a ratio of total hardness to sulfate (([Ca2+] + [Mg2+])/[SO42−] → 1) which enables attaining an almost complete washout of monovalent ions in the DiaNF step. The paper is concluded with presentation of general design of the process steps and a cost assessment, which shows the process to be both flexible in the quality of the rich Mg solution generated, and cost competitive, relative to other alternatives.

Original languageEnglish
Article number41
Pages (from-to)1-13
Number of pages13
JournalChemEngineering
Volume2
Issue number3
DOIs
StatePublished - Sep 2018

Keywords

  • Desalinated water
  • Diananofiltration
  • Mg
  • Nanofiltration
  • Post treatment

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