Long-term Testing near Tucson, Arizona of Concentrate Management using Halophyte Irrigation; Uses Slowsand Filtration (SSF) and Reverse Osmosis (RO) Treatment to Produce the Needed Concentrate
This Science and Technology (S&T) Program research project will answer whether SSF and RO (with associated concentrate management) can effectively treat Tucson area quality Central Arizona Project (CAP) water on a long-term basis.
In a pilot test, sponsored by the S&T Program and completed in 2002, SSF was shown to be effective at an estimated 25 percent of the cost of other treatments. However, the test only operated for 7 months. This study will follow the advice of Leland and Logsdon and conduct pilot tests for longer than 1 year.
The proposed study will evaluate long-term treatment effectiveness for water quality characteristics of CAP water near Tucson, Arizona. Since CAP water is transported over 300 miles from the Colorado River and is blended with Verde River water, it is essential that testing take place near Tucson, Arizona, where a treatment plant is proposed. Because concentrate disposal represents half the cost of treatment by RO, cost-effective and implementable alternatives for concentrate disposal must be investigated.
Need and Benefit
Increasingly stringent water quality treatment regulations combined with the long-term impacts of increased salinity have caused arid region water providers to focus on treatment technologies that will avert long-term problems. Local water quality concerns with CAP water have delayed full use of CAP water in Pima County, Arizona. Current problems with arsenic, perchlorate, and salinity in Phoenix, Arizona; Las Vegas, New Mexico; southern California; and El Paso, Texas offer compelling evidence that a long-term view towards water treatment will reduce the overall cost to rate payers and society, in general.
Developing a low-cost, environmentally friendly treatment that produces high quality water will pay dividends for generations. This technology can be transferred to many cities and towns across the Western United States, including those mentioned earlier. Because of the simplicity of operation of SSF, this technology can be used by rural and Native American populations.
The towns of Oro Valley and Marana as well as the Metro Water District and Flowing Wells Irrigation District have requested Reclamation and the University of Arizona's assistance because of their expertise, unbiased evaluations, and regional perspectives in dealing with water quality and salinity issues. Studies of this complexity are beyond the capabilities of any of the single local water providers. However, with Reclamation's leadership and water resource management capabilities, we are able to bring together the water providers to help them implement an effective long-term water management strategy.
This study will be conducted in a completely coordinated and cooperative effort with the existing S&T SSF/RO study being conducted at the Water Quality Improvement Center (WQIC) in Yuma. The local team of water providers supports that effort and is committed to using the positive results of that study as a starting point in our evaluations. Unlike the Yuma SSF study, we intend to investigate the use of halophyte irrigation as a concentrate disposal option. This very important aspect would allow implementation of this technology at other inland sites like Phoenix, Arizona; Las Vegas, New Mexico; and El Paso, Texas This study will evaluate the applicability of the Yuma SSF/RO study findings to the somewhat different conditions that apply in the Tucson area and in its allotted CAP water composition. In addition, the corrosivity of the SSF/RO product water will be studied to determine its long-term impact on process equipment and downstream distribution systems.
Salt management through a combination of RO for treatment of CRW and irrigation of salt tolerant crops for concentrate disposal will allow reuse of Colorado River water (CRW) for consumptive uses such as agriculture and landscape irrigation. Halophyte treatment of waste concentrates is an innovative technology that addresses Reclamation's need to improve efficiency of water operations and sustain beneficial uses of existing waters for direct use and multiple cycle reuse. The treatment system investigated is expected to provide the lowest-cost regional water supply alternative, thus providing manageable capital and operational costs for sustainable CRW delivery.
There is no long-range plan for salt management for municipalities that depend on the lower CRW resources. Results to date suggest this combination will provide cost-effective CRW treatment if communities can solve their concentrate disposal problems. Cities without convenient access to saline water bodies are the most challenged. This project would both address the aquifer salt degradation issue and the corollary need for a concentrate disposal capability among noncoastal desalting facilities. In addition, we would establish blending requirements to avoid corrosion when distributed water consists of a potential mix of SSF product, SSF/RO product and native ground water.
Independent Peer Review
The following documents were reviewed by qualified Bureau of Reclamation employees. The findings were determined to be achieved using valid means.
Long-term testing near Tucson, Arizona for concentrate management using halophyte irrigation; with associated slowsand filtration (SSF) and reverse osmosis (RO) treatment (final, PDF,
By Martin Yoklic, Wendell Ela and Robert Arnold
Report completed on May 23, 2012
crops for concentrate disposal will allow reuse of CRW RO concentrate for productive use such as agriculture and landscape irrigation.