AWWA MTC64639

In recent years, capital and operating costs of seawater desalination plants have decreased remarkably.However, production of potable water from seawater by reverse osmosis membrane desalinationremains 2 to 3 times the cost of desalting brackish water, reclaiming wastewater, or importing freshwater even over long distances. In addition, rejection of boron by seawater reverse osmosis (RO) membranes is generallynot adequate in one pass system without pH elevation. Further, environmental issues remain anothermajor limitation of seawater desalination, e.g., impingement/entrainment, energy consumption, andbrine discharge. The authors hypothesize that reducing total dissolved solids (TDS), organic, and mineral concentrations of seawater through nanofiltration (NF)pretreatment would allow use of low pressure RO membranes at higher flux (reduced "footprint" andcapital cost), lower operating pressure (reduced energy cost), and higher water recovery (more productwater), thus, reducing the overall cost of water produced. In addition, with reduced scaling concerns theRO process could be operated at high pH, which would enable high rejection of borate. Selectiveremoval of minerals in the NF pretreatment stage further allows utilization of efficient brackish waterconcentrate treatment processes such as chemical precipitation, as well as the option to redirect variousconcentrate and permeate flows to reduce pressures, enhance recovery, and minimize concentrate.This study explores the combination of true NF, brackish water RO(BWRO), low pressure RO (LPRO), and seawater RO (SWRO) membranes to more efficiently andeffectively produce potable quality water from seawater. The objective is to assess whether or not theefficiency and efficacy of membrane-based seawater desalination processes can be improved through theuse of multi-pass/multi-stage arrays. The goals are to reduce cost of desalted water, improve productwater quality, provide multiple-barrier approach, effectively remove boron, and produce a lessburdensome concentrate stream. Further, the authors hope to establish the optimal hypothetical NF/ROmembrane properties needed to best utilize multi-pass/multi-stage arrays for seawater desalination. Includes reference, table, figures.

Product Details

Edition:

Vol. - No.

Published:

03/01/2007

Number of Pages:

6

File Size:

1 file , 350 KB