Boron removal from geothermal water by air gap membrane distillation

In this study, boron removal from geothermal water with an air gap membrane distillation (AGMD) system was examined. The utilization idea of the waste heat sources in geothermal power plants for membrane distillation process is the basis of this research. During the study, six different types of commercial membranes were used and the influence of operating parameters such as feed temperature and velocity, coolant temperature and velocity and air gap distance on the permeate flux and rejection performances were investigated. First, the operating parameters were optimized and the experiments were performed with three different saline water concentrations (0.1-1.5-3% (w/v)). Then, the effect of boron concentration on permeate flux was investigated by using a synthetic geothermal water. Finally, a real geothermal water was used for the determination of AGMD system performance and min. 99.5% boron removal efficiency was achieved for all membranes. The results showed that permeate water boron concentrations were < 0.5 mg/L for all membranes which are in accordance with irrigation standards. As a result, the air gap width, feed velocity and temperature were found as dominant factors affecting the permeate flux. And also, it was observed that feed water boron concentration did not affect permeate water flux.