Reagentless Field-Usable Fixed-Site and Portable Analyzer for Trihalomethane (THM) Concentrations in Drinking Water

U.S. Environmental Protection Agency (EPA) rules stipulate that corrective action be taken for drinking water distribution systems that exceed the maximum contaminant level (MCL) for total trihalomethanes (TTHMs), 80 μg/L. Currently, real-time or even periodic monitoring of drinking water is not economically feasible. Available methods use gas chromatography and are expensive and plagued with long delay times between sample collection and results. Laboratory analysis requires sample collection, packaging and shipping, tracking and recordkeeping, and disposal of samples. A sensor allowing rapid response, real-time measurement of TTHM concentrations in water systems would be ideal for identifying contaminant "hot spots" and allowing system operators to implement mitigation strategies and monitor changes. A team including the principal investigator developed such a sensor in the 1990s--the RCI sensor. This sensor was fabricated from a mixture of rare-earth elements sintered in a silica matrix, a procedure very similar to that used for the heated metal oxide sensor (HMOS). Unlike HMOSs, this RCI sensor was extremely sensitive to chlorinated organic vapors and not at all sensitive to hydrocarbons. The sensor was very effective but relatively large and expensive. The goal of this project is to develop and demonstrate feasibility of a microelectromechanical systems (MEMS) version of this sensor, a prototype analyzer, and simple analytical method that can measure TTHM at concentrations below the EPA-regulated level of 80 μg/L in water. The MEMS approach will yield a modern sensor with a tiny economical footprint and high performance. KWJ recently has developed a MEMS platform on which multiple classes of chemical sensors can be fabricated, including the RCI sensor, and there is opportunity to leverage this work with this SBIR project. In Phase I of this SBIR project, KWJ developed a MEMS planar sensor chip with the rare-earth sensory coating and demonstrated that it is responsive to THMs at low ppb levels. In Phase II, KWJ will integrate the sensor into an analyzer and develop a method for effective monitoring of TTHMs in drinking water that will save significant time and materials and provide a new field capability for environmental protection. In Phase I, KWJ fabricated and tested a MEMS planar version of the sensor, demonstrating the ability to detect less than 5ppbv CHCl3, less than 15ppbv CHBr3 in gas phase, and less than 10 and 20 μg/L, respectively, in water without pre-concentration. The Phase II research effort will focus on optimizing the sensor and sampler design. KWJ will build, instrument, develop, and validate a simple sensor-method with a target of less than 1 μg/L for all THM species. The resulting analyzer will make analytical quality monitoring of drinking water for TTHMs possible virtually anywhere, at any time, on-the-spot, and at low cost. Additional applications made possible will include pool and spa as well as industrial water and groundwater monitoring.