ABSTRACT
Motor oil and industrial detergent were used to prepare simulated oily wastewater. When stabilized with surfactant, the turbidity (Formazin Attenuation Unit, FAU) was found to have a positive correlation with oil content in the emulsion with a correlation coefficient of 2.78 FAU/(mg/L). The oil/water emulsion was tested with filtration, decantation, centrifugation, flotation, and electrochemical coagulation for the effectiveness of each process on demulsification. Electrochemical coagulation was selected for further study. DC voltage was applied to the electrodes, dissolving ferrous ions at the anode and forming hydrogen and hydroxyl ions at the cathode. A few hundred parts per million of sodium chloride was added to the solution to provide ionic conductivity and to prevent passivation of the iron electrode. The ferrous ion was oxidized to ferric ion and that destabilized the emulsion. The coalesced oil droplets adsorbed onto the highly dispersed and reactive ferric hydroxide coagulant. The oil-rich sludge that was generated in the operation was floated to the surface where it formed a blanket that was removed by skimming. The complex mechanism was completed in four minutes. When the reactor was operated at four minutes, the dose of ferric ions generated in the process was 165 mg/L. The treatment reduced the turbidity of the emulsion from 1700 FAU to 60 FAU. The addition of more iron to the system beyond the four-minute treatment period resulted in further change in the turbidity in a much slow rate. In a continuous operation at a current of 2 amperes and a throughput of 320 mL/min, the turbidity of the electrically treated effluent was less than 14 FAU that is the detection limit of the DR/4000 Spectrophotometer.
