The Golden Heart Utilities WTP, which is located near downtown Fairbanks and along the banks of the Chena River, is designed to treat 8 mgd and has an average daily flow of 5 mgd. The original plant was built in 1953, with expansions in 1962 and 1990.
Click here to enlarge imageAll electrical components have intrinsically safe barriers to eliminate potential sparking. Additionally, liquid level sensors are included in the top cell to prevent the system from starting if those levels drop for any reason.
Safety is a major factor when installing and operating this technology. Siemens and its local Service Contractors like TMG Services ensure that plant personnel receive thorough training on how to use the equipment during the initial startup. Also, factory authorized experts are available at all times for long-term service and support.
Hypochlorite Generation
Fairbanks installed the OSEC B2-200 model, which consists of two short skids, in June 2004. Each skid has two electrolyzer cells and a capacity of 250 PPD, for a combined total capacity of 500 PPD of equivalent chlorine.
The hypochlorite generating system produces a low-strength sodium hypochlorite solution of 0.8% through the electrolysis of brine, consuming only salt, water and power. In general, it takes 3 lbs of salt, 2 kW-hours of power and 15 gallons of water to produce the equivalent of 1 lb of chlorine gas.
The water is softened, mixed with a brine solution, diluted and then pumped into special electrolyzer cells that contain cathodes and specially coated anodes. When electricity is applied, electrons flow between the cathodes and the anodes. Chloride ions in the water approach the anodes, donate their electrons and form chlorine molecules – the same chlorine molecules found in chlorine gas.
The low concentration level of 0.8% means the solution is non-hazardous, which eliminates the need to develop a Risk Management Plan. The system has a small footprint, making it easy to retrofit practically any plant. The GHU plant installed the system in its old chlorine gas room, which saved time and money.
The operating water temperature greatly affects reaction efficiency. Because of their unique anode coating, OSEC electrolyzer cells have an operating range of 50 to 80°F. However, when plants have incoming water below that range, it must be heated in order to maintain optimal electrolyzer cell performance. This often requires additional electric heaters, which can add more cost (both capital and operational) to a system.
Since Fairbanks has incoming water that averages 45°F, it needs to be heated accordingly. The OSEC system's unique heat exchanger captures the heat naturally generated during the electrolysis process and circulates it back to the inlet water. This heats the water an additional 5 to 7°F without the use of electric heaters, which has resulted in incremental cost savings over time.
Dave Dean, director of administration at Fairbanks Water & Sewer, said he was pleased with the system, which has actually performed beyond what was expected.
"The GHU plant is using less than 3 lbs of salt and less than 2 kW hours per lb equivalent of generated chlorine," Dean said, "and operating costs are subsequently that much less."
About the Authors:
Sam Fleury is WTP plant foreman for Golden Heart Utilities. He can be contacted via e-mail at [email protected]. Brian Shugrue is western regional manager for the Chemical Feed and Disinfection Group for Siemens Water Technologies. Based out of Leavenworth, WA, he can be contacted at [email protected].