Coal seam gas associated water treatment and management—opportunities and limitations

Abstract

Coal seam gas (CSG) is a new major export for Australia. The production of CSG releases a significant amount of brackish water to the surface, known as associated water. Queensland’s Department of Environment and Heritage Protection (DEHP) has predicted that the peak yearly flow of the associated water could range between 100-280 gigalitres (GL) per year. This presents a major challenge to the CSG industry in water and its by-product (brine) management. CSG water quality varies across regions, but is typically high in total dissolved solids, bicarbonate, hardness, and silica. Consequently, CSG water without treatment is unsuitable for beneficial uses. To date, reverse osmosis (RO) desalination processes with suitable pre-treatment steps have been employed to remove elevated salts and other compounds before CSG water can be used beneficially. One type of beneficial reuse of the treated water that has gained acceptance and prominence in recent times is the irrigation of agricultural crops and forestry. RO brine, a highly saline stream, requires a managed response to ensure a socially, environmentally and financially sound outcome. Conventional evaporation in brine ponds is not considered favourably under existing government directions and, consequently, alternative solutions are sought. Thermal processes, such as brine concentrators, have been used in the treatment of CSG RO brine. The resulting high-quality distillate produced by thermal processes can be used in a number of applications along with a greater proportion of water recovered from such processes. This peer-reviewed paper concludes that a thermal process in conjunction with a high-recovery RO membrane plant, configured as a hybrid membrane/thermal configuration, is probably a suitable solution to meet policy direction by improving system recovery as a precursor to advance associated water treatment and brine management. The discussion is generated out of MWH’s experience with CSG water treatment and management processes, which totals a number of significant projects in the CSG industry.