Development of Hybrid Electrochemical Water Treatment System Combined of Deionization and Oxidation

Abstract

Over recent decades, the lack of available water has been considered as a critical challenge for mankind. Electrochemical water treatment can be a promising alternative due to its high energy efficiency, eco-friendliness and lack of required hazardous chemicals. Capacitive deionization (CDI), electrodialysis (ED) and desalination battery are well-established demonstrations that are successfully converged of materials used for energy storage with electrochemical system for water treatment. These demonstrations accomplish electrochemical deionization by means of the operational principle of energy storage in energy storage systems (e.g., supercapacitors and batteries). Although they provide an energy efficient deionization process, the systems have suffered from the limitations in their systems and materials, attributing to difficulties to find suitable compounds/systems for capturing anions and retain the stability of active material in aqueous system. In this dissertation, it is demonstrated that a novel electrochemical water treatment system combined of deionization and oxidation, and suitable materials for intercalation/deintercalation of cations. First of all, a novel hybrid electrochemical water treatment system consisting of an electrochemical desalination system synchronized with an oxidation process is developed. The hybrid electrochemical water treatment system consists of electrode material for the sodium ion battery as a desalination component and an oxidant generation anode serving the oxidation function. As a primary result, superior desalination capacities of approximately 87 mg g-1 and 36 mg g-1 were accomplished with NaCl concentrations of 35 g L-1 and 3 g L-1, respectively. Moreover, this hybrid system showed a coulombic efficiency in synthetic brackish water (2.79 g L-1 of diverse ions) of approximately 98% and 66% for desalination and oxidation, respectively. Second, a new HCDI system with sodium iron pyrophosphate (Na2FeP2O7) is investigated. The overall deionization performance of Na2FeP2O7 as the electrode capturing cations is demonstrated. The major results of the HCDI system with Na2FeP2O7 showed a superior maximum deionization rate performance (0.08 mg g-1 s-1) with a comparable deionization capacity (30.2 mg g-1) compared to the previous HCDI system with Na4Mn9O18. Furthermore, the analysis of the CDI Ragone plot was applied to investigate the hybrid behavior characteristics, high deionization capacity that originated from the high capacity of Na2FeP2O7 and fast deionization rates resulting from the supercapacitor. Consequently, the novel electrochemical water treatment and electrode materials can contribute to providing a new strategy to overcome the limitations of materials used for capturing anions and discovering their behavior for electrochemical water treatment.