Capacitive deionization technology with multi-stage treatment as an efficient desalination process for agricultural irrigation

Novel capacitive deionization (CDI) technology is recognized as a cheap desalination method and holds a promise to be deployed in low-profit fields such as agricultural and municipal works. In this study, the application feasibility of CDI technology in agricultural irrigation is thoroughly investigated. The desalination performance of three operation methods ("low flow rate", "high applied voltage", and "two-stage treatment") are compared for treating artificial brackish water of 2000 mg L-1 to a set desalination target (600 mg L-1). Among these three methods, "two-stage treatment" overwhelms the other two methods regarding several desalination indicators, achieving a decent productivity (1.5 L h-1 m- 2) with a small energy input of 1.4 kWh m- 3. The modified Donnan model indicates that energy dissipation is mitigated in a high flow rate adopted in two-stage treatment, and meantime a high desalination capacity and a good charge efficiency are achieved. In addition, desalinated water with a salt concentration gradient is produced by the CDI module for tomato seedlings irrigation. Compared with the tomato seedlings irrigated by feedwater (2000 mg L-1), the total length and the biomass weight of those irrigated by desalinated water of 300 mg L-1 increase 51.1 % and 119.8 %, respectively. The research accomplishes a proof-of-concept of the agricultural application of CDI technology, and provides reliable data as the foundation for its future practical operation.