A flow method with photocatalytic oxidation of dissolved organic matter using a solid-phase (TiO2) reactor followed by amperometric detection of consumed oxygen

A photocatalytic sensor for the determination of chemical oxygen demand (COD) using titanium dioxide, based on the use of a pair of oxygen electrodes and flow injection analysis, is described. The measuring principle is based on the direct determination of the oxygen concentration change resulting from photocatalytic oxidation of organic compounds. One of the two oxygen electrodes, the reference oxygen electrode, was utilized to measure the reference signal responding only to oxygen present in the injected samples. Oxygen consumption due to the TiO2-catalyzed photochemical oxidation of organic compounds in samples was monitored with the working oxygen electrode. The COD value of this sensor was calculated as the difference of the currents at reference and working oxygen electrodes, respectively. The operation characteristics of the sensor are demonstrated using artificially treated wastewater as a substrate. The sensor was also applied to the determination of COD in real water samples from dam reservoirs (n = 20) all over Japan. The results were in good agreement with those from the conventional COD methods (i.e., permanganate and dichromate methods).