The beginning of a growing need
Over a decade ago, two of the fastest-growing communities in the United States were forced to make some big decisions. Just southeast of Phoenix in Maricopa County, AZ, the adjacent neighborhoods of Gilbert and Chandler realized that they were not prepared to meet the needs of their growing communities. Knowing that they would need to take action quickly, these suburbs decided to join forces to address what was obviously their most significant concern — water.
Through an intergovernmental agreement, these communities collaborated on building a new water treatment plant. As part of this agreement, both would equally share the building costs, ongoing expenses and the water that the plant produced, with only one exception — the town of Gilbert would operate the facility.
Named for its prime view of the stunning Santan Mountains and designed to meet the regulations (among the most stringent in the country) instituted by Maricopa County and the state of Arizona, the Santan Vista water treatment plant (WTP) went online in 2009.
The appeal of On-site Sodium Hypochlorite generation
Before Santan Vista was built, the team at Gilbert’s original treatment facility, North WTP was most familiar with gas chlorine disinfection. With safety as their highest priority, the award-winning Santan Vista WTP’s design team wanted to get away from the risks as well as the requirements associated with transporting and storing gas cylinders.
By generating disinfectant on-site using the ClorTec® system, the only chemical that would be transported and stored was food-grade salts. As the Chandler WTP, had been operating a ClorTec® OSHG system since 2007, the Santan Vista design team was extremely interested in learning more about this system’s other advantages. After extensive research and speaking with Chandler WTP operators, the decision to choose an OSHG system became clear for both the team and their collaborating communities.
Inside the plant expansion
Before the 2018 expansion, the Santan Vista WTP had two (2) ClorTec® OSHG units that each produce 1,500 lbs of chlorine daily. One was always in use, and the other was used for backup and during maintenance.
The Phase II expansion incorporated several improvements. Because the two existing units had been so safe and easy to use, plant operators and managers made the unanimous decision to install a third system (from the same manufacturer) to boost on-site capacity in anticipation of future population growth.
The new OSHG system is a smaller unit that provides an additional 1,500 lbs per day production capacity. The plant current only runs one of the three units exclusively, meeting daily needs but not yet operating at maximum capacity. The system’s scalable design allows for increased production capabilities when needed.
Since the 2010 Census, Gilbert and Chandler have been among the fastest-growing communities in the United States. Occupying nearly 65 square miles, these areas have grown by 14 percent and 5 percent, respectively, with a total population of more than 500,000.
The Santan Vista WTP serves about 150,000 individuals with high-quality drinking water. Still online, the additional families and businesses are served by the North WTP and Chandler’s WTP, which continues to use OSHG technology.
A job well done
Recognized for two top awards, the Santan Vista WTP’s Phase II expansion proved to be a huge success, proving you can do more with less.
Water & Wastes Digest’s Top Project Award
For sustainability aspects, coordinating with multiple agencies, overcoming unforeseen challenges, and completing a project on time and budget.
Arizona Water Association’s Water Treatment Project of the Year
For success and efficiency in doubling the plant’s water capacity on time and below budget. The project saved $15 million in program costs compared with the original estimate, a 20 percent cost reduction. The award also cited the project team’s strong, collaborative working relationship and the careful planning that minimized shutdown time to maximize facility operations.
OSHG is a safe disinfection treatment method, operating with only three ingredients: salt, water and electricity. At the heart of the OSHG system is an electrolytic cell that facilitates the electrochemical production of chlorine.
Inside the electrolytic cell, chloride ions from the sodium chloride brine are oxidized using a current passed through the cell. Through this electrooxidation process, the sodium chloride brine — used as a feedstock to the on-site generator— is converted into a disinfectant solution of aqueous chlorine.
The finished product is a 0.8% Sodium Hypochlorite (Bleach) solution that is safer than your standard household bleach. This solution is stored in storage tanks before being pumped into the water as needed.
The following equation, aqueous chlorine, is shown as sodium hypochlorite:
Salt + Water + Current → Sodium Hypochlorite + Hydrogen Gas.
OSHG systems maintenance is minimal, involving a visual inspection to see if there is any bridging across the plates in the cells and changing out filters, which last up to two months and are easy to change. If bridging across the cells occurs, operator’s perform a simple acid clean, but that doesn’t happen often. A remote monitoring system helps reduce the need for site visits for maintenance, as does the unit’s clear cell casing design that allows for visibility and easy access to all components. Additional features that add to the system’s safety and efficiency include hydrogen venting of each cell, an updated control system, and a lower operating temperature.
Periodic testing of the brine solution is recommended. It is a simple, specific gravity test that requires three basic items to perform. The test will require a 500ml clear graduated cylinder, a thermometer and a hydrometer. The temperature and hydrometer readings are cross-referenced with a salinity chart to determine if the proper salt concentration is being supplied to the generator. This test requires very little time or effort to perform and ensures that the system is being run efficiently.
Source: Arizona Utility Expands On-site Hypochlorite Generation, Robert Andrews
Choosing the right treatment system
Upgrading your water treatment facility is no small task. From choosing the design team to deciding on the right treatment system, many factors must be considered. Don’t go it alone. Check out this FREE, easy-to-understand, technical brief of the electrochemical generation disinfectants created by Chief Scientist, Andrew Boyle PhD. Click below for more information.