Microfluidic Flow-By reactors minimize energy requirements of electrochemical water treatment without adding supporting electrolytes

Abstract

While electrode material advances show how electrochemical processes can degrade wide range of environmental pollutants, less research exists on how to lower energy requirements for electrolysis through innovation in reactor geometry that control mass transfer. Microfluidic devices with high electrode surface area to solution volume ratios offer unique insights since they can minimize mass transfer limitations in electrochemical reactors and decrease the energy requirements. Shortening interelectrode distances hold promise to overcome charge transfer limitations, which otherwise requires electrolytes addition for low conductivity drinking waters. To examine the interconnected effects of electrode separation distances and solute concentrations on mass transport and energy efficiency, electrochemical treatment using a model water pollutant (nitrite ion) was evaluated in a flow-by microelectromechanical system (MEMS) reactor where the electrodes were ∼ 40 µm apart in microfluidic reactors. The performance was compared to conventional completely-mixed batch reactors with interelectrode distance of 1 cm. The microfluidic reactors showed decrease of electrical energy per order (EE/O) in one order of magnitude with the ability to degrade contaminants with concentrations as low as 5 mg/L without increasing the energy consumption with the absence of supporting electrolytes. This paper presents a promising approach to study and ultimately develop cost-effective electrochemical technologies by optimizing electrode separation distances, instead of increasing salinity which is often required to achieve sufficient conductivity in water but is counter producing low-salt potable drinking water.