Removal of emulsified oil from polymer-flooding sewage by an integrated apparatus including EC and separation process

Removing emulsified oil from polymer-flooding sewage (PFS) is a tough problem during oil field exploitation as the viscosity and emulsification degree of the oily sewage increased with the addition of polymer in the recovery process. This study aimed to propose an integrated apparatus composed of reaction and enhanced settlement process for small footprint and high settlement efficiency. The effects of current density, flow rate and tilt angles of parallel-plate electrodes (APE) were explored using the integrated apparatus in a continuous system. Furthermore, the comparison between field and laboratory experiments was performed. The results showed that the integrated apparatus had higher removal efficiency. For a given current density of 14 mA cm−2, flow rate of 5 L h−1 and APE 80°, the oil and turbidity removal rate of simulated sewage were 96.32% and 97.3%, respectively. Meanwhile, the energy consumption was 2.32 kWh m−3. For on-site sewage, the treatment effects were better and the removal rate of oil and turbidity were 97.2% and 98.2%, respectively. In addition, it was found that the entire EC process was divided into reactive stage and stable stage. The higher the current density, the better purification effect and the shorter time required to reach the stable. As current density increased from 7 to 14 mA cm−2, the stable time decreased from 100 to 40 min while current density increased from 14 to 28 mA cm−2, the stable time changed a little with the removal increased less than 5%. Besides, the results showed that the final removal decreases with the increase of APE, but except APE ɑ which was defined as a special orientation of electrode when the upper end of anode and the lower end of cathode are in a vertical line (Liu et al., 2017) and that a smaller flow rate required longer time to reach the steady stage with a satisfactory purification effect.