Direct As(III) removal from brackish groundwater by vacuum membrane distillation: Effect of organic matter and salts on membrane fouling

• Vacuum membrane distillation was proposed as a solution for direct arsenic removal.
• Vacuum membrane distillation showed high rejection rates for both As(III) and NaCl.
• As concentrations in permeate were always lower than the maximum contaminant level.
• No effect of organic matter and calcium on membrane scaling and fouling phenomena.

Arsenic contamination of shallow ground water is being one of the biggest health threats in the world, particularly in Asia. In this work, vacuum membrane distillation (VMD) was proposed as an advanced solution for arsenic removal. The case study concerned arsenic contamination in Vietnam, where drinking water resources present not only high arsenic concentration (1–3050 ppb) but also high salinity (5–15 g/L). For that reason, synthetic brackish solutions containing NaCl (10 g/L) and As(III) (at different concentrations – between 300 and 2000 ppb) were used as feed solution in this study. As a result, VMD was capable to satisfy As(III) rejection to meet the required standard in the permeate (MCL = 10 ppb). Salt rejection was also very high (>99.5%). The As(III) rejection rate was always stable at high level (>98.5%), irrespective of high feed As(III) concentrations (up to 2000 ppb). With VMD, a pre-oxidation step was not necessary to convert As(III) into As(V), as it is the case for other conventional treatment processes. Furthermore, no effect of organic matter (humic acid) and calcium on membrane scaling and fouling phenomena was observed at the given concentration in this study.