Boron removal by using vacuum assisted air gap membrane distillation (VAGMD)

Abstract

Vacuum-assisted air gap membrane distillation was used to remove boron from different waters in this study. Four different vacuum pressures (0.02 bar, 0.04 bar, 0.06 bar, and 0.08 bar) were applied and air gap membrane distillation (AGMD) configuration was also used to compare the effect of vacuum pressures on the process. Six commercial hydrophobic membranes which have the 110° contact angle value at least were used. Membranes with a 44.18 cm 2 effective area were tested with saline water, synthetic boron solution, and real geothermal water as the feed solutions which is the only study with VAGMD in the literature. Salt removal efficiencies of all experiments were higher than 98.2%. Permeate boron concentrations of synthetic boron solution and real geothermal water were lower than the 0.5 mg/L limit value for drinking water set by WHO and in terms of removal efficiency it means higher than 99% removal efficiency. Vacuum pressures enhanced the water fluxes as expected and also decreased the specific energy consumption. • The use of a supplementary vacuum pump on the AGMD system improved the flux. • Increasing pressures increase flux and GOR without any considerable rejection loss. • Higher than 99% boron removal efficiencies were achieved. • All permeate boron concentrations were obtained below 0.5 mg/L. • Specific energy consumption values did not increase although using a vacuum pump.