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Beneficial and Nontraditional Uses of Concentrate

Project: 02-06 (Phase B)
Type: Report
Year Released: 2006

Program: Principal
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 phases a and b)

Principal Investigator: Jim Jordahl, Ph.D., CH2M HILL, Inc.

Background

Production of low-salinity water from desalination of brackish and seawater results in a byproduct termed “concentrate,” having significantly increased total dissolved solids (TDS) relative to the source water. Concentrate must be properly disposed of, and this disposal is becoming increasingly problematic as the size and number of desalination plants increase. Costs associated with concentrate disposal will become a growing fraction of total membrane plant costs, and difficulties with finding a viable concentrate disposal method have led to the delay and even cancellation of some membrane plant projects. New technical and regulatory approaches to concentrate disposal are desperately needed.

A number of emerging potential beneficial and nontraditional uses of concentrate have been identified, but these generally are either not well-proven or do not provide a final discharge for salts contained in concentrate. Clearly, there is no panacea for concentrate discharge, but it may be possible to develop creative local options for beneficial use. A combination of methods, such as linking more conventional options with beneficial or nontraditional uses, may be the most cost-effective and can provide redundancy, reliability, and potentially some ancillary benefits.

Goals and Objectives

The project provides a comprehensive review and comparison of the full range of alternative uses of concentrate, including feasibility of implementation, economic considerations, and environmental safety, and evaluates both direct uses of concentrate and the potential for recovery and marketing of individual salts separated from concentrate.

Research Approach

1. Collecting and integrating information was the major thrust of the project. It included reviewing a number of recent related major reports; results of Web searches; and results of literature searches by a commercial firm (NERAC). Information was also sought by outreach to AMTA, AWWA, AwwaRF, WERF, SEDA, SCDA, and MEDRC.

2. Project team members attended several conferences and workshops (Salinity Summit, AWWA-MTC, AWWA-ACE, and JWR & DTF workshop) through which important information and contacts were developed.

3. A survey of selected water utilities and agencies was conducted to evaluate future directions in concentrate disposal, including the potential for beneficial and non-traditional uses.

4. Case studies also were obtained from work-in-kind participants to provide a reality check on process of evaluating concentrate disposal options and technologies.

Findings and Conclusions

Oil Well Field Injection: Injection may be technically feasible at some locations, and may be used to aid secondary recovery of oil and gas.

Solar Ponds: Concentrate could be used as a feedstock for a solar pond, from which heat energy could be derived; however, there are major startup and control issues.

Land Application / Irrigation: This can be a viable alternative, especially for smaller facilities close to agricultural areas. Halophytes can increase the range of concentrate salinities used.

Aquaculture: Issues include the existence of a market for the species to be grown, climate, concentrate chemistry and flow rate, and effluent disposal. Effluent will have increased TDS, nutrients, and TSS as compared to concentrate.

Wetland Creation and Restoration: Concentrate could potentially be discharged to naturally occurring or artificially created inland salt marsh areas. Constructed salt marsh areas would likely be more easily permitted than existing sites.

Constructed Wetland Treatment: Treatment wetlands have been tested at an experimental scale for concentrate treatment. Preliminary results indicate contaminant concentrations and water volume can be reduced.

Salt Separation: Technology appears to exist to accomplish the salt separations and recovery, but commercial viability in site-specific applications is uncertain.

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