Flat flexible thin milli-electrode array for real-time in situ water quality monitoring in distribution systems

Drinking water quality along distribution systems is critical for public health. Until now, general end-users have had no effective method to measure the drinking water quality in situ and identify first-hand any violation. In return, there has been no feedback closed-loop of water quality monitoring and a control regime along distribution systems to provide real-time in situ early-warning for water treatment plants. This study targeted this crucial challenge by developing flat flexible thin micro-electrode array (MEA) sensors that integrate multiple types of mm-sized sensors to simultaneously monitor critical water quality parameters (temperature, conductivity, pH, Cl^- and ClO^-). MEA films were directly mounted onto a water tube that simulated a distribution system. Each type of sensor showed high accuracy with an R² value higher than 0.95 in the calibration tests. The shock tests clearly demonstrated the higher sensitivity of the MEA sensors than commercial sensors, and the advantage of integrating multiple types of sensors on a single film for auto-correction. More importantly, the Ag nanoparticle-modified ClO^- MEA sensors showed high selectivity in the presence of competing elements (Cl^-). Four-week tests in tap water revealed the intact structure of the MEA sensors and stable signal output. Overall, the MEAs possessed high accuracy, sensitivity, and selectivity for monitoring water quality. The flat flexible thin material and integrated configuration make the deployment of the sensors easy along distribution systems and at end-user points, and ultimately enable the in situ assessment of water quality in the water infrastructure.