Bureau of Reclamation Banner
Advanced Water Treatment Research --> Environmental Issues

Concentrate Management

All desalination processes have two outgoing process streams – the product water which is lower in salt than the feed water, and a concentrated stream that contains the salts removed from the product water. Even distillation has a “bottoms” solution that contains salt from the vaporized water. The higher concentrated stream is called the “concentrate.” The nature of the concentrate stream depends on the salinity of the feed water, the amount of product water recovered, and the purity of the product water.

To determine the volume and concentration of the two outgoing streams, a mass balance is constructed. The recovery rate of water, the rejection rate of salt, and the input flow and concentration are needed to solve equations for the flow and concentration of the product and concentrate.

Relationships between flows

Figure 1 illustrates the relationships between these parameters.

Parameters highlighted in purple are unknown, Q is flow rate, C is concentration, subscript “f” is for feed, “p” is product, “c” is concentrate, Rec is the recovery and Rej is rejection, both represented as fractions.

Depending on the recovery and rejection, the concentrate stream can range from 2 to 4.5 times higher than the feed concentration. A mildly brackish groundwater desalination system with average rejection of 90% and water recovery of 80% would produce the higher multiplier while a seawater system with 50% recovery and 98% rejection would produce the lower multiplier.Table 1 is an example of a calculation of concentrations and flows. Use any consistent units. You can download the excel spreadsheet with active formulas to make your own calculations.

Table 1. Calculation of product and concentrate flow and concentration

Qf

1,000,000

Qp

750,000

Cf

3000

Qc

250,000

Recovery

.75

Cp

450

Rejection

.85

Cc

10,650

What to do with Concentrate?

Seawater desalination plants discharge this concentrate back to the sea. However, the distribution system must be carefully designed to encourage mixing (see reports #98 and 132 below). High salinity plumes can be avoided by blending the seawater concentrate with tertiary treated municipal wastewater. If the wastewater was originally product from the desalination plant, the blended effluent should closely match seawater composition.

Managing the concentrate from inland desalination plants treating brackish surface or groundwater is a costly proposition. Options for low salinity concentrate are to discharge to surface water through the municipal wastewater plant and landscape irrigation. For facilities with high salinity concentrate, further treatment is needed to recover as much water as possible prior to discharging to lined evaporation ponds. If the area is underlain be a confined deep saline aquifer, deep well injection may be an option. Reports on all of the alternatives are listed by category below.

Reclamation Issues

  1. Reclamation managed water supplies with high natural salt load: the Colorado River Basin Project, Salton Sea, San Joaquin Valley, and the San Luis Valley Project.

  2. Trust lands with declining water quality

See our desalination and concentrate management research with the WateReuse Research Foundation.

Science and Technology Program Projects

ID Title

Date

Contact
584

Desalination Reject Concentration and Disposal Pilot Study

2005

Tom Poulson

3699

Comparative Analysis of Innovative Concentrate Management Systems

2010

Tom Poulson

6551

Long-term Testing near Tucson, Arizona of Concentrate Management using Halophyte Irrigation

2010

Eric Holler

Desalination and Water Purification Research Program Reports

Report Title

Performing Agency

Date

Report #

Multiple Management Method Evaluation

Evaluation of Two Concentrate Disposal Alternatives for the Phoenix Metropolitan Area: Evaporation Ponds and Discharge to the Gulf of California

Bureau of Reclamation

Mar-00

54

Membrane Concentrate Disposal: Practices and Regulations Concentrate database

Mickley & Associates

Sep-01

69

Membrane Concentrate Disposal: Practices and Regulation

Mickley & Associates

Apr-06

123

Treatment of Concentrate

Mickley & Associates

May-09

155

Saline Wetlands and Landscape Irrigation

Eastern Municipal Water District RO Treatment/Saline Vegetated Wetlands Pilot Study

Bureau of Reclamation

Apr-96

16

Halophyte Crops and a Sand-Bed Solar Concentrator to Reduce and Recycle Industrial, Desalination and Agricultural Brines

University of Arizona; Texas A&M University

Dec-98

35

Solar Ponds

Thermal Desalination Using MEMS & Salinity-Gradient Solar Pond Technology

University of Texas at El Paso

Aug-02

80

Secondary Precipitation and Zero Discharge

Evaluation of Precipitative Fouling for Colorado River Water Desalination using RO

Metropolitan Water District of Southern California

Dec-02

85

Zero Waste Brine Management for Desalination Plant

University of Texas at El Paso

Dec-02

89

Volume Reduction of High-Silica RO Concentrate Using Membranes and Lime Treatment

University of Texas at El Paso

Mar-04

108

Zero-Discharge Seawater Desalination: Integrating the Production of Fresh Water, Salt, Magnesium, and Bromine

University of South Carolina

May-06

111

Cost-Effective Volume Reduction of Silica-Saturated RO Concentrate

University of Texas at El Paso

Feb-08

125

Reverse Osmosis Recovery Maximization (abstract)

Carollo Engineers

Mar-08

119

Evaluation and Selection of Available Processes for a Zero-Liquid Discharge System for the Perris, California, Ground Water Basin

Eastern Municipal Water District

Apr-08

149

Modeling Discharge Plumes

Systems Development for Environmental Impact Assessment of Concentrate Disposal

Oregon Health and Science University

Jul-03

98

Systems Development for Environmental Impact Assessment of Concentrate Disposal - Development of Density Current Simulation Models, Rule Base, and Graphic User Interface

Portland State University

Dec-07

132

Deep Well Injection

Using Oil Fields for the Disposal of Concentrate from Desalination Plants: Please Pass the Salt

Texas Water Development Board

Sep-05

112

Thermal Processes

Brackish Groundwater Treatment and Concentrate Disposal for the Homestead Colonia El Paso, Texas

University of Texas at El Paso

Apr-99

32

Dewvaporation Desalination 5,000 Gallon Per Day Pilot Plant

L'Eau LLC

Jun-08

120