Fluoride, iron and manganese removal from brackish groundwater by solar-powered vacuum membrane distillation

Investigations on a solar-powered vacuum membrane distillation (SVMD) system were conducted for removal of fluoride, iron and manganese from brackish groundwater. A commercial capillary membrane module with effective surface area of 0.1 m(2) was used in the SVMD system. Results showed that over 99% salt rejection rate and over 97% removal efficiency of fluoride, iron and manganese were achieved. Total dissolved solids of the permeate water were in the range of 1-10 mg/L while all contaminants concentrations were well below the World Health Organization drinking water guidelines. Condensation efficiency was found to have significant influence on the performance of the SVMD system. During Phase I of the study, the permeate pressure increased almost linearly with the membrane feed temperature due to insufficient condensation, which negatively affected the permeate flux. The highest permeate flux observed was 5.02 L/m(2) h on September 19th, 2016. The corresponding daily production and gain output ratio (GORso) were 2.17 L and 0.26, respectively. In Phase II, a new condenser was installed to enhance the condensation efficiency. Significant improvement of the permeate flux was obtained with the highest permeate flux being 8.84 L/m(2) h on November 5th, 2016. Consequently, much higher daily production (5.00 L) and GORso (0.40) were achieved.