Integrated pressure-driven membrane separation processes for the production of agricultural irrigation water from spent geothermal water

Abstract

The application of different pressure-driven membranes to treat the spent geothermal water to be used for agricultural irrigation was explored in this study. Firstly, individual performances of different commercially available nanofiltration (NF) and reverse osmosis (RO) membranes attached to a mini-pilot membrane test system were studied. For the single membrane test TR-NF and NF90 as NF membranes and TR-BWRO, Vontrone, TR-SWRO and BW30 as RO membranes were employed while combination of TR-NF with TR-BWRO, Vontrone, TR-SWRO and BW30 was employed in the integrated study (with and without pH adjustment).When performances of individual membranes were investigated, the permeate fluxes obtained it was found that there was no significant flux drop with the experimental time (4 h) in all the studies. In terms of boron removals, boron was partially removed in single membrane study as 22.7–23.6% and 30.6–56.8% by NF and RO membranes, respectively. For the integrated NF + RO membrane configuration (without pH adjustment), boron removals were in the range of 42.1–59.4% while 91.3–95.4% of boron removal was obtained in the integrated NF + RO (at elevated pH). It was found that the produced water complied with class I quality with respect to irrigation water parameters with the exception of boron and sodium adsorption ratio (SAR), while the pH of the product water in the integrated NF + RO study at elevated pH was found to be in class III. Hence, produced water will be suitable (class II) for irrigation if 30% of well water should be blended with the product water in the integrated NF + RO studies (with and without pH adjustment) as well as pH adjustment when necessary.