Cost effectiveness of conventionally and solar powered monovalent selective electrodialysis for seawater desalination in greenhouses

Reverse osmosis is the most widely used desalination technology for treating irrigation water. Reverse osmosis removes both monovalent ions detrimental to crops (Na+,Cl−) and divalent ions beneficial for crops (Ca2+,Mg2+,SO42−). Fertilizer must then be added to the desalinated water to reintroduce these nutrients. Unlike reverse osmosis, monovalent selective electrodialysis selectively removes monovalent ions while retaining divalent ions in the desalinated water. This paper investigates the monovalent selectivity and cost effectiveness of the widely-used Neosepta and new Fujifilm monovalent selective electrodialysis membranes in treating seawater for irrigation. Membrane selectivity, limiting current, and resistance are experimentally characterized. These system parameters are inputs to the developed cost model, which determines fertilizer and water savings, as well as operating and capital costs, relative to reverse osmosis; the primary operating cost difference stems from reverse osmosis’s significantly lower energy consumption. Given prices of commercially available membranes, monovalent selective electrodialysis costs an average of 30% more than reverse osmosis. At the projected sales price of Fujifilm membranes, which are still under development, monovalent selective electrodialysis costs an average of 10% more than reverse osmosis; if electricity costs are less than 0.08 $/kWh, monovalent selective electrodialysis is on par with reverse osmosis. Regardless of membrane price and electricity cost, solar-powered desalination is only economical if photovoltaic capital costs are significantly reduced to 0.10–0.20 $/kWh. When monovalent selective electrodialysis exceeds reverse osmosis cost, the financial requirements for competitive monovalent selective electrodialysis (e.g., energy consumption, electricity cost, energy source, membrane cost) are evaluated.