Demonstration Wetlands Treat and Reuse RO Concentrate

Jim Bays of WDBC Member CH2M Hill provides details of the firm’s collaboration with the Arizona Bureau of Reclamation and the City of Goodyear, Arizona, to implement an innovative approach in treatment wetlands.

The City of Goodyear had been looking for a cost-effective alternative to sewer discharge for reverse osmosis (RO) concentrate disposal. Like many cities in the central valley of Arizona, Goodyear is diversifying its water supply, and constructed a large RO facility to create potable water from brackish groundwater supplies. However, with RO treatment comes the challenge of RO concentrate disposal, which has increased the salt and hydraulic load at the nearby water reclamation facility. A solution was needed to treat this brackish concentrate.

In response, CH2M HILL, Reclamation, and the City of Goodyear developed the Goodyear Pilot Wetlands project, which imagines a process of wetland treatment to remove metals and nitrogen from the concentrate, and then to blend the treated concentrate with treated reclaimed water for discharge into natural riparian wetlands and eventually to the Gila River. A pilot-scale demonstration project was developed, comprised of four vegetated treatment “trains.” Trains 1 and 2 are comprised of peat and green waste-based organic media substrates, Train 3 is comprised of a mixed organic compost substrate, and Train 4 uses a peat substrate. This configuration maximizes anaerobic treatment of the concentrate.

Project partners included the City of Goodyear, which provided concentrate and an area to construct the pilot wetlands at the Bullard Water Campus, and the City of Phoenix, which provided laboratory analysis of water, soil, and plant composition.

In developing this treatment train, the team wanted to find out what could grow in this brackish environment with extreme temperatures and organic soil types. Twelve plant species were installed, all native salt-tolerant plants, adapted by evolution to life in arid settings. Three species were found to thrive: saltgrass, Olney’s bulrush, and narrow-leaved cattail. Another species – yerba mansa – also grew well but only when shaded. Among differing soil textures, fine-grained peat media provided the most success in helping these species to establish and grow quickly.

Monitoring of the concentrate levels in the pilot wetlands demonstrated consistent reductions of nitrate by green-waste and compost-amended wetlands. Selenium, arsenic, and chromium also showed a similar trend, with these three contaminants shown to attain state surface water quality standards.

Overall, the project findings illustrate that an RO concentrate wetland treatment system can effectively reduce nitrate and metal contaminants to state standards, reduce concentrate volume seasonally through evapotranspiration by approximately 50 percent, and yield a blended product water equal to or better than ambient Gila River water quality.

Other benefits relative to other methods of RO concentrate disposal include lower energy use and reduced carbon footprint, lower life-cycle costs, greater use for reclaimed water, and finally, restoration of natural riparian and marsh ecosystems. The approach modeled by the Goodyear Pilot Wetlands presents another option for concentrate reuse, management and disposal for inland communities discharging to evaporation ponds or brackish waters, or coastal communities discharging to estuarine or marine waters. With the successes seen in the Goodyear demonstration treatment wetlands, site planning is now underway for full-scale implementation in Arizona’s central valley.

Jim Bays is a recognized leader in the assessment and analysis of aquatic and biological resources and ecosystems. With more than 32 years of experience in the fields of wetland ecology, limnology, wildlife and terrestrial ecology, aquatic biology, and aerial photographic interpretation, his specializations include the planning, design, and assessment of constructed and natural treatment wetlands. Jim has performed comprehensive studies on the water quality and aquatic ecology of a wide range of wetlands, lakes, reservoirs, and estuaries throughout the United States.

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