Real-time in situ sensing of multiple water quality related parameters using micro-electrode array (MEA) fabricated by inkjet-printing technology (IPT)

Water and wastewater treatment processes has been monitored using expensive yet inefficient “single-point” probes that can only measure single parameter at single point without obtaining a complete picture of physicochemical or biochemical status. The study targeted at this crucial challenge by developing novel micro-electrode array (MEA) sensors using ink-jet printing technology (IPT). Multiple mm-sized electrodes were printed on a flexible film for simultaneous monitoring of multiple parameters at high temporal and spatial resolution. The calibration of four types of MEA sensors (temperature, conductivity, dissolved oxygen (DO) and pH) in water solution showed high coefficient of determination (R² > 0.99) between the MEA readings and the parameter targeted. The shock tests demonstrated high accuracy of MEA sensors and rapid response with a reading frequency of 0.1 s, which captured the shock impacts in more details than commercial probes. Furthermore, patterning multiple types of MEA sensors on a single film enables the auto-correction between the parameters targeted and reduces the measurement errors. MEA surface property observed during 4-week immersion into wastewater and waste sludge revealed the intact structure and high mechanic stability. The study clearly demonstrated the unbeatable advantages of MEAs over existing “single-point” probes: compact sensor configuration, multiple-parameter monitoring in a single measurement, easy fabrication and ultra-low cost ($0.2/sensor), which will decode the system “black box”, provide complete dataset for switch control strategy, and enhance the treatment performance at the lowest capital and operational cost.