Evaluation of newly developed reverse demulsifiers and cationic polyacrylamide flocculants for efficient treatment of oily produced water

For treating oily produced water (OPW) originating from the steam-assisted gravity drainage (SAGD) process, we prepared three water-soluble and cationic reverse demulsifiers - poly aluminium chloride and quaternary ammonium salt (PAC-QAS), polyamine (PA), and polyamine and poly aluminium chloride (PA-PAC). Their effectiveness in destabilizing the emulsion and removing oil and suspended solids from OPW and the synergistic effect with cationic polyacrylamide flocculants (CPAMs) were examined through bench-scale and field tests. The effects of chemical properties, injection dosage, and influent water quality on separation efficiency were discussed in detail. Results from microscopic observations and bottle tests reveal that polyamine-type reverse demulsifier could effectively separate oil from OPW. Its surface-active components enabled to induce morphological changes of the emulsified oils in the aqueous phase by absorbing at the oil-water interface, replacing the natural surfactants, and weakening the interfacial film strength, which promoted the collision and coalescence of small oil droplets. The subsequent bridging and sweeping effects driven by flocculant further strengthened the treatment performance. The optimal combination of PA and CPAM-2 could remove up to 90 % oil and 85 % suspended solids from OPW. Compared to flocculant, the insufficient dosage of reverse demulsifier resulted in worse separation, signifying that the demulsification played a more significant role. The correlation of treatment performance obtained from bench-scale and field tests showed that lower chemical dosages were required in the practical application, indicating the economic applicability and operability for oily wastewater treatment.