Citation:

LEE, W., J. G. PRESSMAN, D. WAHMAN, AND P. L. BISHOP. MONOCHLORAMINE MICROELECTRODE FOR IN SITU APPLICATION WITHIN THE BIOFILM OF CHLORAMINATED DRINKING WATER DISTRIBUTION SYSTEMS- Abstract. Presented at WATER QUALITY TECHNOLOGY CONFERENCE, CINCINNATI, OH, November 01 - 03, 2008.

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to present information

Description:

Many utilities in the United States are using monochloramine as a secondary disinfectant as a result of the implementation of the Stage 1 and Stage 2 Disinfectants and Disinfection Byproduct Rules. A recent survey suggests that an additional 12% of drinking water utilities are contemplating a switch to monochloramine in the future. For utilities that use monochloramine or have source water ammonia, nitrification is an undesirable side effect that may result in water quality degradation and subsequent non-compliance with existing regulations. In order to elucidate nitrification phenomena within distribution system biofilm, microelectrode techniques are under development to profile the chemical constituents that lead to nitrifier growth and inactivation. In this research, monochloramine microelectrodes using platinum wire were fabricated and evaluated for use in in-vivo environmental analysis of monochloramine as the disinfectant in drinking water distribution systems. Several researchers have reported the electrochemical behavior of monochloramine sensors using a platinum or gold disk (or electrode) with a flow injection technique. However, they are too large to apply to small volumes. Therefore, we have developed a monochloramine microelectrode for small-scale applications such as distribution system biofilm. The microelectrode was fully examined for its most appropriate potential for measuring monochloramine through cyclic voltammetry testing and was investigated for its characteristics, including selectivity, reproducibility, life time, pretreatment needs, and interference effects. Calibration of the monochloramine microelectrode was conducted using a monochloramine concentration range of 0.62 - 15.8 mg/L (as total Cl2) in pH 8.0 phosphate buffer solution at room temperature (23°C) using stirred conditions. The microelectrode tips had an approximate 20-μm tip diameter, with an angle of 45°. The response time of the microelectrode was less than 30 sec. Calibration in varied Cl2:N ratios (3:1 - 4:1) showed a constant slope and the sensitivity results from the reaction with chloramine rather than the ammonium ion. The effect of the microelectrode tip size on monochloramine performance indicated as tip size increased, the sensitivity increased due to the bigger response area. Current-potential curves were obtained for monochloramine electro-reduction at pH 8.0 through cyclic voltammogram testing. The current increased proportionally to the monochloramine concentration at -350 mV. The resulting calibration curve had a high 0.999 R2. In conclusion, the microelectrodes were fully characterized with monochloramine and exhibited fast, repeatable response times and good signal stability. This research will lead to a better understanding of the monochloramine microelectrode for in situ application within the biofilm of chloraminated drinking water systems and along with other microelectrodes under development, elucidate nitrification phenomena occurring in the biofilm.

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