Low cost desalination of brackish groundwaters by Capacitive Deionization (CDI) – Implications for irrigated agriculture

Abstract Research into desalination of groundwaters for agricultural application in Australia has previously focused on the viability of large scale reverse osmosis plants. Capacitive Deionization (CDI) is an alternative method of desalination that has been demonstrated to be effective for desalting moderately saline (brackish) waters in pilot studies and can be powered using photovoltaics. Using a farm scale economic model coupled to a CDI performance model, potentially viable agricultural applications for CDI have been identified with variation in crop type and CDI configuration enabling optimisation. Scenarios for grapes, oranges, almonds, apples and tomatoes were modelled with maximum internal rates of return (IRR) and annualised profits (AUD$/ha/yr) determined. Groundwater bore salinity thresholds above which the regime is not feasible were found to be 4.2 dS/m for grapes, 5.5 dS/m for oranges, 4.4 dS/m for almonds, 14 dS/m for apples and 8.5 dS/m for tomatoes for a 60 ha crop with an investment period of 10 years. Costing of CDI desalinated water was scenario dependent with a large portion falling below AUD$1/kL. CDI desalination was found to be economically feasible for a range of scenarios and should be explored further as an option to assist with global water and food security concerns.