Brine Minimization in Desalination of the Geothermal Reinjection Fluid by Pressure-Driven Membrane Separation Processes

Abstract

Brine obtained during water treatment by pressure driven membrane processes remains the major drawback. Therefore, it is of paramount important to find a lasting solution in order to minimize its production by both nanofiltration (NF) and reverse osmosis (RO) membranes. In this study, an experimental study with the aim of brine minimization during membrane desalination of the geothermal reinjection fluid using a mini-pilot scale membrane test system having spiral wound NF and RO membranes was conducted. The membranes employed for this task were TR-NF and BW30-RO membranes. First, studies with different brine to feed ratios of 1:4, 1:3, 1:2 and 2:3 represented as NF-F2, NF-F3, NF-F4 and NF-F5, respectively were investigated using TR-NF membrane. A control study with no brine recirculation was conducted as well in order to check the effect of brine recirculation on the membrane performance. Secondly, studies with BW30-RO membrane using same brine to feed ratios as in the case of NF membrane studies were carried out. An applied pressure of 15 bar, initial water recovery of 60% and 4 h of experimental time were employed as operational conditions for both NF and RO membrane studies. Based on the results obtained, it was found that the brine recirculation (with a brine to fresh feed ratio of 2:3) has a significant impact on the permeate flux. The product water can be utilized for the agricultural irrigation purposes. Nevertheless, the boron concentration in the product water was still high for the sensitive crops.