Water fluoridation is the controlled addition of fluoride to a public water supply in order to reduce tooth decay, as cited 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 contrast, only about 6% of the world’s population drinks fluoridated water.
A Delicate Balance
The precise control of fluoride levels is paramount to the health and safety of the public. Results of even slightly above-average recommended amounts of fluoride can lead to discoloration, unpleasant odor and taste of the city’s water supply. In the U.S., the optimal level of fluoridation ranges from 0.7 to 1.2 milligrams per liter (mg/L), 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 mg/L leaves the risk for fluorosis. Consumption of water exceeding 10 mg/L fluoride has been shown to lead to pathological changes in bone structure, and skeletal fluorosis. Thus, it is critical that the injection of fluoride be as precise and consistent as possible.
The peristaltic pump has been running about 3,200 hours without maintenance issues.
A New Approach
Dusty Martin, the water treatment plant chief operator of the Orange Water and Sewer Authority (OWASA) located in Chapel Hill, N.C., was content with his present 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 as well as at universities worldwide, Martin was curious to compare a peristaltic pump in that same application.
The Jones Ferry Road Water Treatment Plant can treat up to 20 million gal per day (mgd) of raw water 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 mgd. 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 backup. Each pump is able to do 120 gal per day, 24/7. The fluoride output is generally in the range of 63 mils/min or about 1 gal per hour. 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 Supervisory Control and Data Acquisition (SCADA) system for monitoring and alarm responses.
The fluoride pump easily hooked up into the authority's SCADA system.
Successful Application
Martin stated that he was amazed how easily the peristaltic pump hooked up into their SCADA system. Continual 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 very 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. Furthermore, he added that the peristaltic pump is not affected by any air pockets that may enter the system through the day tank. Overall, Martin highly recommends a peristaltic pump over a pulsating pump for fluoride injection.
Additionally, Martin has installed peristaltic pumps on all of his chlorine injection, both on the pretreatment and finish water sides. All in all, the peristaltic pump has proven very reliable and accurate for many chemical injection applications associated with water treatment.
