TREATMENT OF CUTTING OILY WASTEWATER BY ELECTROCOAGULATION/ FLOTATION (ECF):REACTOR CONFIGURATIONS AND OIL CONCENTRATION

Abstract

This work aims to study the treatment of the stable cutting oil emulsion by the eletrocoagulation/flotation process (ECF). Effects of current density, electrode gap, oil concentration, and reactor type on the treatment performance were determined. Three oil concentrations of 0.5, 1.0, and 1.5 g/l were used. The ECF was operated in the bubble column reactor (BCR) and the external loop airlift reactor (ELALR). Moreover, the configuration of the downcomer for the ELALR was also investigated. Finally, the ECF with the optimal configuration from the batch experiment was tested in the continuous operation. It was found that the ECF can effectively treat the cutting oil emulsion with the highest efficiency higher of 99% in the batch operation. The electrode gap of 2.5 cm and the current density of 100 A/cm2 were obtained as the appropriate configuration. The oil concentration can affect the reaction time as the highest efficiency can be achieved at 60, 90, and 120 minutes for 0.5, 1.0, and 1.5 g/l oil concentration, respectively. In addition, similar treatment efficiency can be attained from the operation in the ELALR but with less oil sludge production. The best downcomer in this work was the 135º tilt-up with 100 cm height and 5.1 inside diameter. The ANOVA analysis was also conducted in order to specify the important parameter on the process performance. The current density and the reaction time were found to be the parameter governing the treatment efficiency. Finally, the best configuration of the ECF in both BCR and ELALR were tested with the continuous operation. The efficiencies were slightly decreased in both cases as the wastewater was constantly fed into the reactor. The flow pattern in the reactors was also analyzed by the residence time distribution (RTD). The flow in the columns can be separated into 2 zones including (1) the plug flow zone under the electrodes and (2) the CSTR zone from the electrodes onwards. Furthermore, the dead zone was also observed in the ELALR. These flow patterns can affect the process performance and could be used for improving the overall treatment efficiency.