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Carbon-Fiber Nitrite Microsensor for In Situ Biofilm Monitoring
Citation:
Lee, W., D. Wahman, P. Bishop, AND J. Pressman. Carbon-Fiber Nitrite Microsensor for In Situ Biofilm Monitoring. Presented at International Water Association World Water Congress and Exposition, September 16 - 21, 2012.
Impact/Purpose:
To inform the scientific community
Description:
During nitrification, nitrite is produced as an intermediate when ammonia is oxidized to nitrate. It is well established that nitrifying biofilm are involved in nitrification episodes in chloraminated drinking water distribution systems with nitrite accumulation occurring during incomplete nitrification. Subsequently, the accumulated nitrite may react with monochloramine, accelerating chloramine residual loss (AWWA, 2006). Due to the inability to measure nitrite at the microscopic level in biofilm, our knowledge on the transport and fate of nitrite in the presence of chloramines is incomplete. Microsensors represent one option for in situ biofilm nitrite monitoring, both spatially and temporally. Several studies have focused on electrochemical nitrite determination using microelectrodes (Silva et al., 1996, Okabe et al., 1999, Zhao et al., 2003). However, these studies either used linear sweep voltammetry, which is not suitable for spatial and temporal nitrite measurements, or a potentiometric microelectrode with an ionophore that is no longer commercially available. Therefore, this research sought to develop a new amperometric microsensor that would be suitable for measuring biofilm nitrite concentrations. Carbon fibers are often employed as an electrode material in medical use because of their resistance to drift when exposed to biological tissue and are attractive for in vivo use because of their small size (7-35 µm) (Kawagoe et al., 1993). In this research, a needle-type carbon-fiber microsensor (7-10 µm tip diameter) for in situ nitrite monitoring was developed, fully characterized, and evaluated for biofilm application. The developed sensor showed excellent performance for nitrite measurement with a fast and stable electrode response over a wide concentration range (0-20 mg N/L), including drinking water relevant nitrite concentrations (0-1.0 mg N/L). The developed nitrite microsensor represents an essential tool for elucidating nitrifica