Effect of geothermal water composition and pretreatment on the product water for boron-sensitive crops

Abstract

The membrane filtration is an effective way to produce water for human consumption, industrial use, or irrigation purpose. In this study, a brackish water reverse osmosis (BWRO) membrane was practically investigated to obtain irrigation water from geothermal water. The quality of the produced water was analyzed to understand the potential in agricultural use for boron-sensitive crops. The effects of the feed solution composition and pretreatment by microfiltration were studied. Results showed that the ionic content was effective in reduction of permeate flux. However, the rejections of salt and silica did not change significantly by the change in the feed water composition and they were successfully removed from the geothermal water by more than 95% rejection. Pretreatment of the geothermal water with a microfiltration (MF) membrane having a pore-size of 0.8 μm provided higher flux than the one having a pore size of 5 μm. The higher rejections of boron were only achieved with increased pH in the pretreatment. The pH of 9.5 in the geothermal water provided a rejection of boron as 75% with a permeate boron concentration of 2.4 mg/L when 15 bar of operating pressure was employed. This level of boron concentration in the irrigation water was found to be allowable only for some boron resistant crops (e.g. beans, lettuce, onion) and semi-sensitive crops (e.g. sunflower, potato, tomato).