The U.S. Environmental Protection Agency’s (EPA) Water Infrastructure Resiliency and Finance Center, in collaboration with the...
Dissatisfied with traditional chlorine gas and onsite generation systems, two water authorities in the Southwest have switched to the Accu-Tab tablet chlorination system from PPG Industries to reduce costs, improve safety, boost quality and reliability, and minimize maintenance.
Located about 30 miles southeast of Phoenix, the Chandler Heights Citrus and Irrigation District system was originally designed for irrigating citrus groves. Today, it serves 825 residential connections and a few remaining citrus operations over a 2-sq-mile area. Three wells feed into two tanks with multiple chlorine injection points. The average treatment rate is 1 mgd, with a peak rate of 1.3 million gal.
Facing issues with its 10-year-old chlorine gas system, the district decided to pursue another system.
“We had continuous problems with the gas injector filter clogging, and we also had to rebuild the gas regulator about every six months at a cost of $728 just for parts,” said Gene Rose, project manager for E2 Consulting Engineers, Inc., which designs and manages operations for the Chandler Heights system. “We were also facing higher gas transportation costs, and safe storage and operation was an ongoing concern.”
E2 began evaluating alternative systems, looking at liquid bleach and the Accu-Tab calcium hypochlorite system. After determining that a liquid bleach system had increased safety and environmental regulations and larger storage requirements, E2 selected the Accu-Tab PowerPro FM3150 system.
“We liked the Accu-Tab system’s operating simplicity and safety,” Rose said. “It also costs less to operate and maintain, and we can use a level II certified operator to save about $5 an hour in labor costs. In addition, we could install the system ourselves to further reduce costs.”
Chandler Heights’ upgraded system, which included a new piping system; redesigned flow for improved efficiency; and the Accu-Tab system, came online in late March 2005. Results include chlorine residuals of 0.70 mg/L and a system pH of 7.3.
“The operators have commented on the consistency of the chlorine residual throughout the distribution system compared to the previous gas system,” Rose said. “They also said it holds the residual longer and was easy to install. The entire upgrade, including the installation of the Accu-Tab system, went very smoothly. By doing it ourselves, we saved $35,000 in construction costs.”
Previous reliability and cost issues with onsite chlorine generation convinced North Star Domestic Water Consumers to select the Accu-Tab system for a new surface water treatment plant. Since start-up in April 2004, the plant has experienced zero downtime and minimal maintenance expenditures.
Located in Aztec, N.M., North Star serves 850 residential and light commercial customers through a 100-mile pipeline distribution system. The new plant, which is located on remote property and designed to operate mostly unstaffed, treats an average of 225,000 gpd, with a total capacity of 1 million gal. Water is drawn from the nearby Animas River.
“With onsite chlorine generation, we experienced a loss of residuals at the end of the system and frequent maintenance issues,” said Lloyd Ayliffe, general manager of North Star. “It was a hassle to deal with and extremely expensive to operate and maintain. When it came time to select a system for the new plant, my predecessor decided to go with the Accu-Tab system because of its reliability and low cost.”
North Star’s plant uses two Accu-Tab PowerPro Dual 3075 systems to chlorinate pre- and post-filtration and maintain residuals of 1.6 ppm in the summer and 1.2 ppm in the winter, as validated by the system’s computer data logging equipment. To protect against the loss of chlorine residuals experienced with onsite chlorine generation, the facility also has two backup PowerPro units for use on the 100-mile supply line in the event additional chlorination may be required during an emergency period. Neither has been activated since plant startup.
“We’re able to set the residuals to what we want and then hold them with minimal problems,” Ayliffe said. “Our operating costs are now about 25% less than what we experienced with onsite chlorine generation. We’re so pleased, I’m considering a similar system for one of the other water authorities that I manage.”
The NSF-listed Accu-Tab system combines a simple, patented chlorinator with slow-release calcium hypochlorite tablets to provide consistent and controllable chlorine dosages regardless of size and demand. Accu-Tab PowerPro systems include all components necessary for a turnkey chlorination system and are easily adaptable for automatic control and multi-point injection. The compact system does not require a separate-entry building or room like gas systems and takes up a fraction of the space required for similar bleach or onsite chlorine generation systems. In most cases, maintenance is reduced to cleaning the chlorinator just once a year.
The 3-in. Accu-Tab scale inhibitor calcium hypochlorite tablets, also NSF-listed, are specifically formulated to help prevent scale formation inside the chlorination chamber, especially in hard-water areas. The tablets are pressed rather than formed, ensuring their physical integrity and eliminating brittleness and extensive breakage.