Monochloramine Microelectrode for In-Situ Application Within Chloraminated Distribution System Biofilm

A monochloramine microelectrode with a tip size between 5 and 15 μm and using platinum wire was successfully designed, fabricated and characterized for in-situ monochloramine measurement within chloraminated distribution system biofilm. The monochloramine microelectrode showed sensitivity toward monochloramine concentrations (0.54 to 16.1 mg Cl2/L) at an applied potential of +550 mV (Ag/AgCl reference electrode) at pH 8.0 and 23°C. The monochloramine microelectrode has successfully measured monochloramine microprofiles with high spatial resolution (50 μm) without biofilm structure disruption during measurements. Ultimately, this research will lead to a better understanding of the monochloramine microelectrode for in situ application within a chloraminated drinking water system biofilm, and along with other microelectrodes (e.g., ammonia, pH, DO) under development, elucidate nitrification phenomena occurring in the biofilm. Introduction As a result of the implementation of the Stage 1 and Stage 2 Disinfectants and Disinfection Byproduct Rules, chloramine use as a secondary disinfectant in the United States is predicted to increase to 57% of all surface and 7% of all ground water treatment systems [1]. A recent survey suggests that an additional 12% of drinking water utilities are contemplating a switch to monochloramine in the future [2]. 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 the current research, monochloramine microelectrodes using platinum wire were fabricated and evaluated for use in in-vivo environmental analysis of monochloramine as the disinfectant within chloraminated water distribution system biofilm. Several researchers have reported the electrochemical behavior of monochloramine sensors using a platinum or gold disk (or electrode) with a flow injection technique [3, 4, 5]. However, these electrodes are too large to apply at the small scale (~10 μm), and there is currently no commercial or developed microelectrode for application to biological analyses, including direct measurement of biofilm monochloramine penetration. This study developed monochloramine microelectrodes and investigated their biological applicability, determining biofilm monochloramine profiles. The monochloramine microelectrode was fully examined using cyclic voltammetry, allowing determination of the appropriate applied potential for monochloramine measurement, and was evaluated for its application to various environmental conditions. Deleted: within