Developments in high recovery brackish water desalination plants as part of the solution to water quantity problems

This paper reviews three ways in which existing brackish water reverse osmosis (BWRO) desalination plants can be modified to increase overall water recovery from the 70–75% range to the 90–95% range. The three techniques used to increase plant recovery are: (i) seawater reverse osmosis (SWRO) for water recovery on the BWRO brine stream; (ii) ZeeWeed® ultrafiltration immersed membranes for water recovery from the multi-media filter backwash; (iii) Crystallizer + ZeeWeed® ultrafiltration immersed membranes to increase the recovery of the SWRO. Details of the three techniques, along with detailed water chemistry data from an existing 22,710 m3/d brackish water treatment plant in Saja’a, Sharjah Emirate, UAE will be presented to show the recovery increases possible from each technique. Limitations to further recovery increases will also be identified. In addition to the technical details, basic data are presented to provide an economic comparison (US$/m3) of these alternatives in comparison to current costs for seawater desalination.

The options presented here for increasing recovery of brackish water desalination plants have incremental costs ranging from $US0.22 to $US0.57/m3, using BWRO brine recovery, filter backwash recovery and crystallization/UF as pretreatment to a BWRO brine recovery system. In the Saja’a drinking water treatment plant, it is estimated that these three techniques combined can increase the overall plant recovery from 73 to 95%, saving over 6,072 m3/d or 2.22 million m3 annually. In addition to making better use of scarce water resources, these techniques are cost effective when water costs are compared to seawater desalination water costs. Finally, governments already operating brackish water treatment plants can employ any one of these options to increase the productive life of their well field and the operating life of their existing brackish water treatment plant assets.