Survey of High Recovery and Zero Liquid Discharge Technologies for Water Utilities
Project: 02-06 (Phase A)
Year Released: 2008
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board, Water Research Foundation, Water Environment Research Foundation, City of Phoenix
Total Investment: $435,844.24 (Cash: $395,000, In-Kind: $40,844.24, includes multiple phases)
Principal Investigator: Michael Mickley, P.E., Ph.D., Mickley & Associates
Due to their high cost, high-recovery and zero liquid discharge (ZLD) systems used in various industries are not currently used at any municipal sites. Because of increasing challenges to disposal of concentrate, these types of systems will, by necessity, eventually be applied in municipal settings. There is thus a need to develop realistic performance and cost analyses for high-recovery and ZLD processing schemes.
Goals and Objectives
The project evaluates the costs of commercially available volume minimization and ZLD processing schemes over a range of size, salinity, and water composition variables. In addition to identifying and characterizing processes and developing performance and cost projections, regulatory issues associated with use of the technologies have been identified and are discussed.
Since there are no HR (including ZLD) municipal desalination plants in the U.S., project research began with identification of commercial HR processing schemes used in other industries. Five general processing schemes were found to account for most of the 120+ ZLD sites in the U.S. Detailed performance and costs of these five processing schemes were developed over a range of size, salinity, and water composition variables. Performance and costs of selective salt recovery processing (a commercial process outside of the U.S.) and of three commercial high performance technologies were also developed. Regulatory issues associated with the HR production of brine or mixed solids (the final wastes for disposal) were analyzed.
Findings and Conclusions
- Performance and cost of HR (including ZLD) systems are highly dependent on salinity and composition.
- HR systems are multi-step processing schemes and the dependence of individual process step performance and cost on salinity and composition varies considerably. Consequently, simplified analyses of HR performance and costs may be subject to considerable error.
- High costs of HR processing are associated with capital cost and with energy, chemical, and final waste disposal costs.
- While major capital cost reduction may depend on the development of alternative desalination technologies there are promising means for reducing energy, chemical, and solids disposal costs.
- Second stage membrane processing prior to thermal evaporative processing significantly reduces energy costs by reducing the size of the evaporator. Increased chemical costs and solids disposal costs, however, can offset a substantial portion of the energy cost savings.
- Technology for selective recovery of commercial grade salts has been developed, patented, and licensed outside of the U.S. It warrants consideration as a means of reducing disposal costs, reducing the environmental footprint, and providing an income stream for desalination plants.
- Detailed analysis of concentrate need be done to determine if HR processing might result in final wastes (brine or solids) containing problematic amounts of contaminants.