Treatment of RO brine from CSG produced water by spiral-wound air gap membrane distillation — A pilot study

Brine management is a major bottleneck for coal seam gas (CSG) production in Australia. This study investigated the concentration of CSG reverse osmosis (RO) brine using a pilot membrane distillation (MD). The system was equipped with a novel spiral-wound air gap membrane distillation (AGMD) module. By operating the pilot MD system at low feed temperature and a small temperature gradient, a stable distillate production rate could be maintained. The resulting low permeate flux can be offset by a high packing density of the spiral-wound membrane module. Here, using a module with diameter, height, and total membrane surface area of 0.4 m, 0.5 m, and 7.2 m2, respectively, the pilot MD system sustainably achieved 80% water recovery and produced 10 L/h of distillate from CSG RO brine. Overall, 95% water recovery could be obtained from CSG produced water for beneficial uses by a combination of RO and AGMD without any observable membrane scaling. A preliminary thermal energy demand analysis suggests that if installed in New South Wales (Australia), 1 ha of flat-plate solar thermal collector arrays could provide sufficient thermal energy to treat 472 m3/day (2970 bbl/day) of CSG produced water using the proposed RO/AGMD treatment train. Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.

Pilot treatment of CSG produced water by a combination of UF/RO and MD was demonstrated. Overall, 95% of CSG produced water could be recovered by the hybrid system for beneficial uses. The UF/RO recovered 75% fresh water from the raw CSG produced water and the pilot MD system extracted 80% fresh water from the RO brine. The low permeate flux of the pilot MD system was offset by the high packing density of the AGMD module used. Despite being operated at 80% water recovery, the distillate production rate was stable throughout the pilot study possibly because of the addition of anti-scalant to CSG produced water and the small operating temperature gradient. However, mass-balance calculation indicates the possible precipitation of silica and calcium, which may pose a scaling risk in long-term operation. When operating in continuous mode, the STEC and SEEC of the pilot MD system were stable at 250 and 1.1 kWh/m3, respectively, and a GOR of 2.5 was achieved. The integration of solar thermal energy into the MD system was considered. In New South Wales (Australia), 1 ha of flat-plate solar thermal collectors can provide sufficient thermal energy for the treatment of 118 m3/d of CSG RO brine using AGMD.