Recycling of coal seam gas-associated water using vacuum membrane distillation Farideh Heidarpour, Jeffrey Shi and So-Ryong Chae ABSTRACT 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 ¼ 15 mS/cm). To study performance of the VMD process, we explored the effects of feed temperature (T f ¼ 60, 70, and 80 W C), feed flow rate (V f ¼ 60, 120, and 240 mL/min), and vacuum pressure (P v ¼ 3, 6, and 9 kPa) on water permeability through the PTFE membrane in the VMD process. Under the optimum conditions (i.e. T f ¼ 80 W C, V f ¼ 240 mL/min, P v ¼ 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. Farideh Heidarpour Jeffrey Shi School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, NSW 2006, Australia So-Ryong Chae (corresponding author) Department of Biomedical, Chemical and Environmental Engineering, 701 Engineering Research Center, University of Cincinnati, Cincinnati, OH 45221-0012, USA E-mail: chaesg@ucmail.uc.edu Key words | coal seam gas-associated water, fouling layer, operating conditions, PTFE membrane, vacuum membrane distillation INTRODUCTION Coal seam gas (CSG) is a natural gas extracted from low and high rank coals and contains more than 98% methane, less than 2% of CO 2 and trace amount of nitrogen compounds (Nghiem et al. ). Mass production of CSG results in large quantities of brackish water as a by-product dominated by sodium, bicarbonate, and chloride (Moore ). The chemical composition of coal seam gas-associated water (CSGAW) is complex and varies considerably depend- ing on the geographic location, depth of the coal bed, composition of the rocks surrounding the coal beds, amount of time for reaction between water and rock, and the origin of the water entering the coal beds (Averina et al. ). CSGAW may also be contaminated with drilling chemicals contain heavy metals, carcinogens such as ben- zene, toluene, ethylbenzene and xylene, and radioactive elements like uranium (Lloyd-Smith & Senjen ). Australia has rich CSG potential with estimated resources of 4.3 Tm 3 and production of 6.2 Bm 3 in 2013. The National Water Commission in Australia estimated at least 300 GL (giga-litres) of CSGAW per annum has been produced in 2012, which is accompanied by 31 million tons of salts as by-product (Leather et al. ). A major challenge in CSG production is how to manage a large volume of potentially harmful by-products before they release to the environment (Wang et al. ). Appli- cations of CSGAW without treatment for irrigation have been shown to change physical/chemical properties of soil, and can exceed acceptable salinity level for sensitive crops ( Johnston et al. ; Brinck & Frost ; Zhao et al. ). The release of CSGAW to the land may cause precipitation of calcium carbonate in soil, and eventually may cause a reduction in the infiltration rate and increase runoff and erosion (McBeth et al. ). Surface disposal of CSGAW may drown vegetation and cause erosion, as well as degrading grazing lands (Freij-Ayoub ). If CSGAW spills into creeks or rivers, it can endanger the aquatic life. Current treatment technologies for desalination of CSGAW include reverse osmosis (RO), freeze–thaw/evapor- ation (FTE), ion exchange (IE), capacitive deionization (CDI), electrodialysis, distillation, ultraviolet light, and 908 © IWA Publishing 2015 Water Science & Technology | 72.6 | 2015 doi: 10.2166/wst.2015.229 Downloaded from https://iwaponline.com/wst/article-pdf/72/6/908/466309/wst072060908.pdf by guest on 07 July 2020