Zhiheng Xu

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.

Self-sustained high-rate anammox: from biological to bioelectrochemical processes

The slow growth rate of anammox bacteria is a pressing problem for system efficiency and stability. An innovative solution was explored in this study that involves accelerating anammox in microbial electrolysis cells (MECs) and alleviating their dependence on anammox bacteria. Batch tests showed that 85% of total nitrogen (TN) was removed in the MEC system, whereas only 62% of TN was removed in conventional anammox. Simulation of the modified Nernst–Monod model revealed that the maximum specific utilization rate (0.30 to 0.38 mmol g−1 VSS h−1) in the anammox MEC was 60% higher than in conventional anammox (0.18 to 0.20 mmol g−1 VSS h−1). Harvesting the power generated in microbial fuel cells (MFCs) to support the MECs substantially saved energy consumption and effectively utilized the low power output of MFCs. Simulation of the power management system (PMS) interface demonstrated the charge/discharge cycles for power supply by the MFCs and for power consumption by the MECs. The integrated MEC-MFC system accelerated anammox, required no external carbon source, effectively utilized wastewater energy, and thus achieved self-sustained nitrogen removal.