Water sensor for testing fluoride concentrations in groundwater to improve drinking water quality in developing countries




Vail, Caitlin

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Excess fluoride in groundwater used for drinking can pose serious health hazards, especially in poor, rural areas of the developing world lacking water treatment. The World Health Organization recommends a maximum fluoride contaminant level of 1.5 mg/L in drinking water [1]. Over 200 million people in low- and middle-income countries currently drink groundwater over that limit [2]. Current field detection of fluoride typically uses HACH kits, with several groups developing smartphone based alternatives [3]. These methods are based on colorimetry. The HACH kit is limiting because appropriate training is required, results are sensitive to competing ion contamination and chlorine, the glassware must be clean, and repetition is needed to ensure reliability [4]. The use of a smartphone for in-field detection of fluoride is promising and takes a strong step towards quick, easy, reliable, and portable fluoride detection. Our research takes the concept of a portable device one step further by using a fundamentally different, and simpler, mode of detection. We have demonstrated the use of optical fibers as an alternative, non-colourimetric fluoride detection method. The tip of a single mode optical fiber is coated with a thin film of Al and is immersed in an aqueous fluoride solution. The reaction between fluoride and the Al coating changes internal reflection proportional to fluoride concentration which is measured by a photodetector as an output voltage. We made great steps in optimizing the methods, materials, and code required for this sensor. Additionally, we built a device to allow approximate standardization of Al thickness as a function of the distance from the target and time of sputtering. We established the best practical thickness of Al coating, improved repeatability between sputter deposition events, and implemented an optical switch into the experimental set-up.



Water Sensor, Optical Fibers, Drinking Water, Fluoride