Coal seam gas water treatment for beneficial reuse

Coal seam gas (CSG) extraction is widely practised in Australia and many other parts of the globe. The by-product of gas extraction is ground water and is commonly called CSG-produced water. The volume of CSG-produced water is large and is expected to rise, as the CSG industry in Australia and elsewhere continues to expand. The produced water is currently treated with reverse osmosis (RO) where both fresh water and brine are produced. The brine is 25% of the original water, and if the right extraction method is executed, further fresh water recovery is achievable. This study assessed the feasibility of CSG RO brine minimisation, by employing a pilot scale multi-effect distillation (MED) system. Samples were collected from two gas wells in Gloucester known as Craven 06 (CR06) and Waukivory 03 (WK03). Throughout the course of the study, the MED system was operated continuously at absolute pressure of 25 kPa. In each pilot evaluation trial, higher water recovery was attainable with water recovered from WK03 and CR06 greater than 95 and 97%, respectively. The MED performance showed near complete salt removal and distillate conductivity readings of 0.041 mS/cm and 0.022 mS/cm for WK03 and CR06, respectively. The distillate production was stable, averaging a flow rate of 16 to 17 L/h. The average feed flow rate was 21 L/h. High levels of thermal stability showed no evidence of scaling affecting the temperature inlet solution, with marginal decline in heat transfer coefficient, due to increasing the concentration ratio from eight to 10 times. The overall performance confirms that MED can be used for further treatment of CSG RO brine. The study recommends that concentrate from the MED to be reused for reclaiming minerals, to facilitate zero-liquid discharge and offsetting treatment costs (from the sale of suitable minerals i.e. sodium hydroxide or sodium bicarbonate).