Compact fluidic electrochemical sensor platform for on-line monitoring of chemical oxygen demand in urban wastewater

The rapid expansion of urban areas has given rise to the generation of large amounts of wastewater that pose a \ngrowing pressure on the surrounding ecosystems. Effective water quality surveillance programs demand the \nimplementation of in-field tests to monitor water safe discharge in the environment after being adequately \ntreated. This paper describes the manufacturing and application of a miniaturized electrochemical sensor for \nmeasuring dissolved chemical oxygen demand (COD) in surface waters entering and exiting urban wastewater \ntreatment plants (UWWTP). Thin-film carbon electrodes are produced on Si/SiO2 substrates by a combined \nsol–gel material synthesis and photolithography/dry etching process at the wafer level and show superior \nelectrochemical performance compared with the glassy carbon standard electrode. Three-electrode electrochemical \ncells of planar configuration are produced and the COD sensor is manufactured by electrodepositing \ncopper nanoparticles (Cu NPs) on the working electrode under controlled potentiostatic conditions. A simple \nfluidic electrochemical sensor device is fabricated and allows for the Cu NPs electrodeposition as well as \nanalytical sensor performance in an automatic fashion. A linear range up to 670 mg⋅L-1 O2 and a limit of \ndetection of 30 mg⋅L-1 O2 are achieved. The ability of this electrochemical sensor approach to monitoring the \nsoluble organic load of urban wastewater in real-time is evaluated by analyzing three samples collected in \ndifferent locations of an UWWTP. The COD values estimated with the sensor are in excellent agreement with \nthose obtained using the standard dichromate method provided by an accredited laboratory. This analytical \nplatform provides a robust, user-friendly low-maintenance flow sensor approach for deployed analysis of COD \nthat could aid to control the effectiveness of water treatment processes, especially when facing water influents \ncontaining organic overloads due to changing weather conditions or any anthropogenic phenomena.