Improving groundwater quality for irrigation using monovalent selective electrodialysis

Abstract

Monovalent selective electrodialysis (MSED) is a desalination technology that allows for the selective removal of monovalent ions that are detrimental to crops, while retaining divalent ions that are beneficial for crops. This paper proposes a semi-empirical MSED model that can be used to evaluate desalination system performance for different salinities of brackish source water. The MSED set-up is a discretized stack modelled as an electric circuit, consisting of ohmic resistances and membrane potentials for each ion species. The model is coupled and simultaneously validated with MSED experiments. These experiments determine applied current density and ion transport numbers, which serve as the primary inputs to the model. The model outputs are the concentration change of each ion species across the stack and the system energy consumption during steady operation. Ion concentration differences represent membrane selectivity towards monovalent/divalent ions (Na+/Ca2+ and Na+/Mg2+). Evaluation of MSED membrane performance in the brackish salinity range will help determine the conditions that optimize membrane selectivity and energy consumption, as well as the technology’s suitability for agricultural applications.