Treatment of a worn mineral oil effluent by electrocoagulation using aluminium electrodes

Abstract

Water pollution by oils is more and more a preoccupation because of its increasing occurrence and the hazard to human life and environment. Depollution of oily effluents can sometimes generate a secondary pollution (with chemical coagulation / flocculation processes) or be very costly (ultracentrifugation). In this work, electrocoagulation with aluminium electrodes was applied to the treatment of a worn mineral oil effluent. For this to be achieved, the influence of the pH and the current density on the turbidity and organic matter was first investigated. A liquid-liquid extraction was then carried out on the oil samples in order to isolate hydrocarbons and study their behaviour. Finally, these hydrocarbons were analysed by gas chromatography (GC-FID) to evaluate their removal efficiency. The results obtained showed that optimal conditions were as follows: initial pH=7 and current density = 10.98 mA.cm-2. The results obtained with a supporting electrolyte concentration set at 0.5 mg.L-1 showed that optimal conditions were as follows: initial pH=7 and current density = 10.98 mA.cm-2.) In these conditions, the turbidity was almost totally eliminated and organic matter removal efficiency was 93.30%. Analyses of the various chromatograms showed that 98.83, 99.56 and 93.02% respectively of aliphatic fraction, unsaturated hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) were eliminated during electrocoagulation of the worn mineral effluent. However, the absence of regular peaks was observed on the chromatograms, and that was due to unidentified heavy PAHs. Thus, FID did not seem sensitive enough to identify and characterize PAHs compounds based only on retention.