Treatment of an in situ oil sands produced water by polymeric membranes

Cross-flow ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) were applied for the first time on a produced water obtained from a thermal in situ bitumen recovery process called steam-assisted gravity drainage (SAGD), with the intent to remove salt, silica, and dissolved organic matter (DOM) so that the produced water could be re-used as high-quality boiler feedwater. It was found that more hydrophilic and more negatively charged membranes were less susceptible to fouling. The UF membrane tested rejected a maximum of 30% of the salt and silica and 50% of the DOM. Nanofiltration with loose membranes removed more than 70% of the salt and DOM. The tight NF membranes tested removed more than 86% of the salt, silica, and DOM, and consumed less energy than RO, which showed almost the same rejection. An instantaneous increase in water flux resulting from a step change in feedwater pH demonstrated the critical role of pH in flux recovery and in fouling mitigation. Analysis of the fouled membranes indicated presence of silica, iron, and calcium in the foulant material. Feed and permeate characterization showed that mainly hydrophilic DOM passed through the membrane. The study provides valuable insights regarding the suitability of membranes as alternatives to conventional SAGD water treatment methods, especially in terms of producing higher quality recycled water.