Arizona correctional facility reduces TDS with reverse osmosis system
In 2013, AdEdge Water Technologies LLC was contacted by Valentine Eng. to participate in a design/build project that was ongoing at the Red Rock Correctional Center facility in Eloy, Ariz. CCA is the parent company and is an operator of privately owned and operated prisons throughout the U.S.
CCA signed an agreement with the state of Arizona to administer up to 1,500 prisoners at the Red Rock site in Eloy, Ariz. Before the contract could begin, the well supplying the facility, which was high in total dissolved solids (TDS), had to be treated to assure the TDS was less than the 500 mg/L secondary maximum contaminant level for potable drinking water. The TDS of the raw well water is approximately 865 mg/L, so a reverse osmosis (RO) system was required. The system had to utilize a blend of raw well water into the RO permeate water to produce a final blended water quality with TDS less than 500 mg/L.
The ADRO8-4L-5H reverse osmosis system was custom designed to allow field upgrade in the future as water usage increases in the facility. The current system produces up to 140 gal per minute (gpm) of the blended product, with the blend ratio being 80 gpm of RO permeate to 60 gpm of raw well water. The RO system is integrated to the well pump and distribution atmospheric storage tanks so the RO runs as water is required in the storage tank.
The system also includes an antiscalant feed system to protect the RO membranes from fouling due to water hardness and silica. A second chemical feed system is incorporated and doses NaOH (sodium hydroxide) to the final blended product to increase pH, which will reduce potential for corrosion in the piping system. A pH controller is interfaced to the RO and chemical feed pump maintaining a final pH in the 7.5 to 7.6 range.
The system was also provided with a CIP (clean in place) system, which will allow cleaning of the RO membranes on site (without removal from the RO pressure vessels). The system operators have been trained to monitor the system operating pressure and flow rates and when certain conditions are reached, the CIP cycle would be performed. CIP cleaning includes use of low pH and high pH cleaners to primarily remove biofilm and organic scaling due to hardness minerals (calcium and magnesium) and silica in the raw well water.
The system was started up and put into operation in February and March 2014. The system is currently providing a final blended product to the facility with approximately 450 mg/L TDS. Since system operation, the TDS has been treated below the treatment goals.