New Strategies for Managing Desalination Concentrate with Zero Liquid Discharge from Two WRF Research Projects

The need for affordable inland desalination in the U.S. is urgent. Many utilities are struggling to meet growing water demands and manage increasing salinity levels in their fresh water sources. The greatest challenge faced by utilities wishing to desalinate inland water sources is concentrate management. Discharge of concentrate to surface waters or deep well injection raise environmental concerns and these alternatives are increasingly difficult to permit. Discharge to a wastewater treatment plant simply recycles salinity or passes it on to a downstream user. The alternative is zero liquid discharge (ZLD) treatment. In ZLD, concentrate is treated so that the water is recovered for beneficial use and there is no discharge of liquid waste from treatment. Desalination with zero liquid discharge is the subject of two recent AwwaRF research projects. The technical approach in both projects involves treating RO concentrate to reduce its membrane fouling potential prior to a second desalination step. The report for the first project, Zero Liquid Discharge for Inland Desalination, was published in 2007. The research involved computer modeling, bench-scale testing and pilot-scale testing. The research results were used to estimate cost and energy requirements for the proposed approach and compare them to those for the established ZLD approach using thermal desalination and evaporation ponds. It was estimated that treatment costs and energy consumption could be reduced by 50 to 70 percent with the proposed treatment approach.