The most common desalination technology for treating brackish irrigation water is reverse osmosis (RO). RO yields product waters low in monovalent ions that are harmful to crops (Na+ and Cl–) and in divalent ions that encourage crop growth (Ca2+, Mg2+, and SO4 2–). Fertilizer or divalent-rich brackish water must be mixed with the desalinated water to reintroduce these nutrients. Monovalent selective electrodialysis (MSED) provides an alternative to RO that selectively extracts monovalent ions while retaining divalent ions. This paper investigates the monovalent selectivity and potential of the new cost-effective Fujifilm MSED membranes to treat brackish source water in greenhouses, with a comparison to the widely used Neosepta MSED membranes. Thirteen groundwater compositions serve as feedwater to an MSED experimental setup to characterize membrane selectivity, ion transport, limiting current, and membrane resistance. The Fujifilm membranes demonstrate notable selectivity for all compositions. On average, they remove six sodium ions, compared to Neosepta’s four, for every calcium ion and 13 sodium ions, compared to Neosepta’s seven, for every magnesium ion, while their bench-scale cost is 68% lower than that of the Neosepta membranes. The Fujifilm selectivity values are used to calculate annual fertilizer savings of MSED relative to RO, which average $4995/ha for 6000 brackish groundwaters across the United States.

Reverse osmosis is the most widely used desalination technology for treating irrigation water. Reverse omsosis removes both monovalent ions detrimental to crops (Na + , Cl − ) and divalent ions beneficial for crops (Ca 2+ , Mg 2+ , SO 2− 4 ).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 of competitive monovalent selective electrodialysis (e.g., energy consumption, electricity cost, energy source, membrane cost) are evaluated.

The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. CitationAhdab, Yvana D. et al. "Treatment of greenhouse wastewater for reuse or disposal using monovalent selective electrodialysis."

Das MSED-Entsalzungsverfahren stellt eine neue Technologie für die Aufbereitung und Reinigung unterschiedlicher Agrarwässer dar. Hierbei besteht das größte Anwendungspotenzial in der Entsalzung von brackigem Grundwasser zur Pflanzenbewässerung.