In-field one-step measurement of dissolved chemical oxygen demand with an integrated screen-printed electrochemical sensor

The increasing awareness of the importance of water for human and environmental health has prompted the need for developing fast, user-friendly and cost-effective analytical approaches for quality control and management. This work reports the fabrication and analytical assessment of a very simple sample-to-result electrochemical sensor for discrete and precise measurements of dissolved chemical oxygen demand (COD) in water samples of urban wastewater treatment plants (UWWTP). The device is fabricated by screen printing and shows a three-electrode cell configuration including a working electrode made of a composite material comprising a porous carbon matrix and copper nanoparticles, synthesized by a customized one-pot sol-gel process. The key feature of this device is the implementation of a paper disk loaded with sodium hydroxide covering the electrochemical cell area that allows sample filtering and pH conditioning. Thus, analytical measurements are carried out by casting a 20 mu L sample drop without requiring any further user intervention. The overall sensor fabrication process can be scaled up for cost-effective mass manufacturing. The feasibility and performance of this integrated device are first evaluated using glucose as a standard analyte. A linear range up to 400 mg L-1 O2 and a limit of detection of around 26 mg L- 1 O2 is achieved, this being well below the EU legal concentration limit of 125 mg L-1 set for effluents of UWWTPs. Three real samples are analyzed in the lab as well as on-site and COD sensor values are in agreement with those obtained with the standard dichromate method at a certified laboratory, within the error limits. This miniaturized novel sensor platform greatly simplifies the standard analytical procedure for measuring COD, facilitating rapid decentralized analysis for precise control of urban wastewater treatment.

Automated summary

The need for fast, user-friendly, and cost-effective analytical approaches to water quality control and management has increased as the importance of water for human and environmental health is being recognized. This study presents the fabrication and assessment of a simple electrochemical sensor for measuring dissolved chemical oxygen demand (COD) in water samples from urban wastewater treatment plants (UWWTP). The sensor is fabricated using screen printing and includes a three-electrode cell configuration with a working electrode made of a composite material containing a porous carbon matrix and copper nanoparticles. A unique feature of this device is the use of a paper disk loaded with sodium hydroxide to filter the sample and condition the pH. The sensor allows for measurements by casting a small sample drop without any further user intervention. The fabrication process can be scaled up for mass production. The sensor's performance is evaluated using glucose as a standard analyte, and it shows a linear range up to 400 mg L-1 O2 with a limit of detection of 26 mg L-1 O2, well below the EU legal concentration limit for UWWTP effluents. Real water samples were also analyzed, and the COD sensor values were found to agree with those obtained using the standard dichromate method at a certified laboratory. This miniaturized sensor platform simplifies the analytical procedure for measuring COD, allowing for rapid decentralized analysis and precise control of urban wastewater treatment.