An efficient and accurate method of pumping fluoride into a municipal water treatment distribution system.
Water fluoridation is the controlled addition of fluoride to a public water supply to reduce tooth decay as specified by the Center for Disease Control and Prevention. It is estimated that about two-thirds of the U.S. population uses water that has been fluoridated from our municipalities. In stark contrast, only about 6 percent of the world's population drinks fluoridated water.
The precise control of fluoride levels is paramount to health and safety of the public. Even slightly above average recommended amounts of fluoride, though not considered dangerous, can lead to discoloration, unpleasant odor and taste in the city's water supply. In the United States, the optimal level of fluoridation ranges from 0.7-to-1.2-mg/L (milligrams per liter, equivalent to parts per million), according to the Center for Disease Control and Prevention. Depending on the average maximum daily air temperature, the optimal level is lower in warmer climates, where people drink more water, and is higher in cooler climates.
The World Health Organization cautions that fluoride levels above 1.5 milligrams per liter can increase the risk of fluorosis, a disease in young children that causes discoloration and damage to teeth. Consumption of water exceeding 10-mg/L of fluoride has been shown to lead to pathological changes in bone structure and skeletal fluorosis. It is critical that the injection of fluoride be as precise and consistent as possible.
Case Study
The WTP chief operator, Dusty Martin, of the Orange Water and Sewer Authority (OWASA) located in Chapel Hill, N.C., was content with the use of pulsating pumps for the fluoride system. However, since the Jones Ferry Road Water Treatment Plant serves as a model for state-of-the-art improvements and is routinely used as an engineering maintenance example for the engineering students studying at the local university and universities worldwide, Martin was curious to test a peristaltic pump in that same application.
The Jones Ferry Road Water Treatment Plant can treat up to 20 million gallons of raw water daily drawn from two nearby sources, University Lake and the Cane Creek Reservoir. Daily water use by the 70,000 people in the Carrboro-Chapel Hill area averages about 9 million gallons per day. The water treatment process encompasses several phases. The first phase is the addition of powdered carbon to the water supply from the lakes to improve the taste and control odor in the water. Secondly, the solid particles are separated from the water in settling tanks. Once that process is complete, the water is then filtered through layers of sand and anthracite coal. Lastly, chemicals are added for disinfection and public health. The chemicals include chlorine, ammonia and fluoride. Although fluoride is not necessary, it is encouraged by the Board of Dental Health and approved by both the N.C. State Public Water Supply and the OWASA.
The fluoride (H2SiF6) treatment process consists of using one primary pump and one back-up. Each pump is able to do 120-gpd, 24/7. The fluoride output is generally in the range of 63-mils/min or about 1-gph. The fluoride process treatment is the final chemical stage before the water is sent to the channel of finished water. The pumps are wired via 4-20mA into the SCADA (Supervisory Control and Data Acquisition) system for monitoring and alarm responses.
Martin stated that he was amazed how easily the peristaltic pump hooked up into their SCADA system. Continuous monitoring using powerful graphic and alarm software programs allow the SCADA system to ensure the exact amount of chemicals have been dispersed into the water supply. Presently, the peristaltic pump has been running about 3,200 hours without any type of maintenance issues. The tube life is generally the major concern for peristaltic pumps, but in this application little output pressure is experienced.
Most importantly, Martin cites that the dosing is much more precise, accurate and consistent using a peristaltic pump compared to a pulsating pump. He added that the peristaltic pump is not affected by any air pockets that may enter the system occasionally through the day tank. Overall, Martin highly recommends a peristaltic pump over a pulsating pump for fluoride injection.
Additionally, Dusty Martin has installed peristaltic pumps on all of his chlorine injection, both on the pretreatment and finish water sides. The finish water stage injection sees 80-psi, and the peristaltic pump has performed well. All in all, the peristaltic pump has proven reliable and accurate for many chemical injection applications associated with water treatment.
Pumps and Systems, April 2009
