Recycling of coal seam gas-associated water using vacuum membrane distillation

Coal seam gas-associated water (CSGAW), which is a by-product of coal seam gas (CSG) production typically contains significant amounts of salts and has potential environmental issues. In this study, we optimized a bench-scale vacuum membrane distillation (VMD) process with flat-sheet hydrophobic polytetrafluoroethylene (PTFE) membranes for the treatment of synthetic CSGAW (conductivity = 15 mS/cm). To study performance of the VMD process, we explored the effects of feed temperature (T(f) = 60, 70, and 80°C), feed flow rate (V(f) = 60, 120, and 240 mL/min), and vacuum pressure (P(v) = 3, 6, and 9 kPa) on water permeability through the PTFE membrane in the VMD process. Under the optimum conditions (i.e. T(f) = 80°C, V(f) = 240 mL/min, P(v) = 3 kPa), water permeability and rejection efficiency of salts by the VMD process were found to be 5.5 L/m(2)/h (LMH) and 99.9%, respectively, after 2 h filtration. However, after 8 h operation, the water permeability decreased by 70% compared with the initial flux due to the formation of fouling layer of calcium, chloride, sodium, magnesium, and potassium on the membrane surface.