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.

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 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