H-2 bubbles produced at the cathode are beneficial for improving mass transfer within a batch electrocoagulation (EC) reactor. Increasing the thickness of the electrolytic bubble layer along the vertical electrode affects the distribution character of the oil concentration. This study aimed to explore oil removal from three layers relative to a series of vertically distributed aluminum electrodes; this type of exploration is crucial to understanding the demulsification process. The four factors of the initial pH, temperature and concentration of sodium chloride and the surfactant were investigated. Most micrometer-sized oil droplets on Layer A were obviously removed within the first 4 min, regardless of the sewage quality. The optimal pH value was 7.0, and the optimal NaCl concentration was 2 g L-1, which were demonstrated by the improvement in the overall demulsification performance. An increase in the emulsion temperature reduced oil removal from Layer C. Improvement in the oil removal efficiency of both Layer B and C was found to be crucial to the support of the overall demulsification process within the EC reactor. This result forms the basis for the industrial design of EC reactors and a way to determine its capacity in a variety of situations. (C) 2019 The Electrochemical Society.

This study aims to optimize the electrocoagulation(EC) process of emulsified oil removal from polymer-flooding sewage (PFS), producing in the oil recovery process and characterized by multiple chemical additives, high viscosity, and high stability. Response surface methodology (RSM) and Box-Behnken statistical experimental design (BBD) were applied to investigate the effects of tilt angles of electrodes, flow rate, and current density as well as the interactions on oil removal and energy consumption. All the experiments were performed in a continuous-flow pattern with an integrated unit combined with reaction and subsequent separation zone. The experimental results suggested that EC technology was very efficient in oily wastewater treatment and was able to achieve 97% oil removal after the system enters into the stable stage with a flow rate of 5.5Lh−1 ，applied current density of 18.9mAcm−2 and tilt angle 80°. At this time, the energy consumption is 3.50kWhm−3. Besides, for both of the oil removal and energy consumption, flow rate has the most significant impact, and the current density follows. The results of variance (ANOVA) analysis showed a high correlation coefficient (R2)value of 0.990 and 0.996 for oil removal and energy consumption, respectively, which ensures an adequate fit of the second-order regression.

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 a 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.

On marine oil spill, inflammable lightweight oil has characteristics of explosion risk and contamination of marine enviroment, therefore treatment of stable emulsion with micron oil droplets is urgent. This study aimed to propose a combined electrocoagulation and magnetic field processes to enhance performance of lightweight oil recovery with lower energy consumption, The effects of current density, electrolysis time, strength and direction of magnetic field on the overall treatment efficiency of the reactor were explored. Furthermore, the comparison between coupling device and only electrocoagulation through tracking oil removal in nine regions between the electrodes. The results were shown that the permanent magnets applied was found to enhance demulsification process within electrocoagulation reactor. For a given current density of 60 A m(-2) at 16 min, Lorentz force downward was proved to promote the sedimentation of coagulants. As the magnetic field strength increases from 20 to 60 mT, oil removal efficiency was observed to increase and then decrease, and simultaneously energy consumption reduced and then present constantly. The results were found that the magnetic field strength of 40 mT was optimal within electrocoagulation reactor, which can not only diminishe difference of mass transfer rate along the height of vertical plate but also consume lowest energy. (C) 2018 Elsevier Ltd. All rights reserved.