Evaluation of Alternatives to Domestic Ion Exchange Water Softeners
Project: 08-06
Year Released: 2014
Type: Scientific Investigation
Program: Principal
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board, Santa Clara Valley Water District, City of Phoenix, City of Scottsdale
Total Investment: $236,201.52 (Cash: $154,943.52, In-Kind: $81,258)
Principal Investigator: Peter Fox, Ph.D., Arizona State University
Background
Consumers desire softened water for a variety of reasons. The removal of calcium and magnesium ions has the potential to improve the properties of the water for a number of applications. Many of these perceived benefits cannot easily be quantified. Examples of such benefits would include the effectiveness of detergents for cleaning clothes or how a shampoo makes a person’s hair look and feel.
The use of domestic ion exchange water softeners can become a major source in the overall urban contribution of total dissolved solids (TDS) in wastewater because of the concentrated brine discharged during regeneration of ion-exchange water softeners. Increasing TDS at water reclamation facilities will ultimately hinder the reuse of reclaimed water.
Goals and Objectives
The project evaluates alternatives to domestic ion exchange technologies for their ability to prevent scale prevention and alternative technologies with different types of water. Two different surface waters, Colorado River water (the most widely used water in the southwestern United States) and a groundwater, were tested. Another secondary objective was using life-cycle assessment to determine the impact of the technologies on water energy use.
Research Approach
The technical approach included:
- Literature review to document prior studies and identify the most promising emerging alternative technologies.
- Identification of the testing methodology to be used to evaluate the devices: the German DVGW-W512 protocol.
- Design and construction of the testing apparatus.
- Testing of waters of varying hardness across the range of test units.
- Analysis of the results and calculation of the Effectiveness Factor for each test unit.
Findings and Conclusions
- All of the devices tested were able to reduce scale formation.
- Capacitive deionization and ion exchange efficiently reduced scale formation.
- Template assisted crystallization reduced scale formation by greater than 88 percent.
- Both electromagnetic treatment and electrically induced precipitation reduced scale formation by approximately 50 percent.
- The ability to reduce scale formation was not a function of the water type, although there were major differences in the quantities of scale formation between water types.
- The scale formed with no treatment control was a hard scale (calcite) and acid washing was necessary to remove the majority of the scale.
- The scale formed after electromagnetic and electrically induced precipitation was a “soft” scale that was easily removed by brushing. Review of X-ray diffraction results and scanning electron microscope images exhibited differences in the crystal orientation of the calcite scale between the different technologies.
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