Brackish water desalination for greenhouse agriculture: Comparing the costs of RO, CCRO, EDR, and monovalent-selective EDR

Abstract

Greenhouses are a rapidly growing agricultural sector that uses desalination systems. However, the desalination requirements of the greenhouse industry and an economic evaluation of desalination technologies for greenhouses have not been reported previously. Several greenhouse operators in North America using desalination systems were interviewed to identify key design specifications. A detailed cost comparison was conducted for key technologies: reverse osmosis (RO), closed circuit RO (CCRO), electrodialysis reversal (EDR) and monovalent selective EDR (MS-EDR). Capital, energy and membrane replacement costs, savings in feedwater costs from operating at higher recovery, and potential savings in fertilizer from using MS-EDR, were calculated. For <10-hectare greenhouses, RO was the most cost-effective technology. For >10-hectare greenhouses, alternatives can be considered. MS-EDR is economically competitive if it can retain at least 20% of the calcium and magnesium needed for growing and if membranes last 7 years. CCRO is competitive if the sum of feedwater and brine disposal costs are >$0.24/m3. If this cost was $0.32/m3, additional investment over RO for CCRO, EDR and MS-EDR, could pay itself back in 2.4, 3.4 and 2.1 years. In Ventura county where municipal water costs $1.05/m3, RO, CCRO, EDR and MS-EDR had payback periods of 7.1, 8.4, 7.8 and 8.2 months.