Challenge
The city of Scottsdale, Arizona, a community of more than 200,000 residents was historically totally dependent on groundwater resources. By the mid 1980's, the city began putting together a multi-faceted water resource program to provide the community with a long-term sustainable water supply.
The city of Scottsdale owns and operates a 13.5 million-gallon-a-day Central Groundwater Treatment Facility (CGTF) with approximately 80,000 service connections. It was decided that disinfection methods needed to be converted from chlorine gas to a safer alternative, to eliminate the transportation of the compound throughout the community. The city of Scottsdale prides itself on being one of the country's leading cities in terms of environmental conservation and stewardship, and was committed to finding a solution for water treatment that was both eco-friendly and the safest possible option for the community and its residents.
Solution
Since the start-up of the CGTF in the early 1990's, a conventional Wallace & Tiernan® chlorination system supplied by Evoqua Water Technologies was used. Chlorine was supplied by two one-ton cylinders--one in service and one in reserve. In 2007, after researching several systems, City and water officials determined that on-site chlorine generation was the best and safest choice for disinfection. Safety was even more top-of-mind for this conversion project because the facility is located in a residential area and situated immediately adjacent to a community park. For this conversion project, the City again turned to Evoqua for a high-quality, safe and reliable solution. The CGTF rehabilitation project was also on a tight timeline and needed to be constructed in the existing plant footprint without interrupting water production.
The design-build construction team managing the project selected the installation of two OSEC® B-Pak 500 on-site hypochlorite generation systems and four peristaltic hose pumps from Evoqua to replace the existing gas feed equipment. The OSEC B-Pak system is a fully automated, pre-packaged product that is designed for fast and economical installation, safe operation and easy maintenance. Skids are shipped completely piped, wired and tested.
The system generates a sodium hypochlorite solution through the electrolysis of brine, utilizing only water, salt and electricity.
During the four-month period when the old chlorination system was taken off-line and the new equipment was installed and started up, the plant purchased sodium hypochlorite from a local vendor and stored it in tanks that fit into the space previously occupied by the chlorine scrubber.
Results
The converted plant has been operating successfully since late 2009. Since only salt is necessary to operate the OSEC B-Pak system, chlorine gas is no longer being transported through the Scottsdale community to treat the drinking water supply.
Since startup of the onsite generation system at the CGTF, the City of Scottsdale has partnered with Evoqua on additional conversion projects at the 70-mgd CAP plant which treats Central Arizona Project water from the Colorado River, and the City's AWT plants, which supply 20 mgd for turf irrigation and groundwater recharge. In both projects, the conversion from gas chlorination to on-site generation was implemented without interruption of water production by retrofitting existing chlorination structures.
Four good reasons for choosing OSEC® electrolyzers
- Safe process design and automated controls
- Reliable, robust design
- Cost effective, high efficiency
- Delivers high-quality sodium hypochlorite 0.8%