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United Utilities PLC, operator of regulated water, wastewater and electricity distribution networks in northwestern England, reports continued satisfaction with the ClorTec onsite sodium hypochlorite generating system from Severn Trent Services. Installed in March 2004, the system provides a cost effective, reliable and safe alternative to stringently regulated and increasingly costly chlorine gas and bulk sodium hypochlorite disinfection methods. United Utilities' water and wastewater network serves a population of approximately 7 million.
The ClorTec onsite sodium hypochlorite generation system is approved for potable water within the United Kingdom and is compliant with ATEX requirements. The unit produces 11.9 pounds per day of chlorine equivalent using salt, water and electricity as its raw materials. The system operates by feeding softened water into a brine dissolver. The salt dissolves to form a brine solution, which is further diluted to the desired salt solution. The salt solution is then passed through electrolytic cells, which apply a low voltage DC current to the brine to produce the sodium hypochlorite. The sodium hypochlorite is then safely stored in a day tank, and when it reaches the low-level set point, the system automatically restarts to replenish its supply. The unit typically requires operator visits once a week in order to keep appropriate levels of salt in the brine tank.
Since the ClorTec unit produces sodium hypochlorite on-demand, the technology alleviates the problem of chlorate byproduct generation that typically results with the storage of bulk sodium hypochlorite. The ClorTec system also features clear acrylic cells, which allow the reaction of salt, water and electricity to be visible and maintenance issues to be obvious. The split flow of brine to the cell ensures the economical, low chlorate production of 0.8% sodium hypochlorite solution.
According to Stan Hill, water process engineer at the United Utilities site, the company selected the onsite generation system for its safety and cost efficiency. "Health and safety features are key to the design of the system," said Hill. "The equipment allows us to eliminate the safety risks of transporting and storing chlorine gas. The system has proved reliable, too. Since its installation, only routine system maintenance has been required."