Treatment of cutting oil/water emulsion by coupling coagulation and dissolved air flotation

Abstract

On a purely comparative basis with former studies, the physicochemical treatment of cutting oil emulsion was applied to two different mineraI oils ( A and B). The preliminary tests of destabilization showed that the sulphuric acid and the ferric chloride do not allow an appreciable destabilization for emulsion prepared oil A, whereas for the oil B, only the calcium chloride was effective. The kinetics of separation, arises in the decreasing exponential form and shows an optimal amount in coagulant agent dose. It is noticed that the turbidity of the cutting oil emulsions of oil A are more significant than oil B. For the same concentration, in consequence of an unquestionable difference in their composition. Whatever the type of oil used, the calcium chloride gives a better effectiveness of separation, and reduction in turbidity. Also, the emulsions prepared with oil B are more stable, quality desired by the users, but as more easily destabilized and treated than oil A; the reduction of turbidity equalizes to 99%. Although the chemical treatment decreases in a considerable way, the organic load of the emulsions (oil-water), the residual COD remains significant. To this end, the study of the coupling dissolved air flotation (DAF), with the chemicaI treatment was carried out. An average diameter of air micro bubbles (50 μm) obtained for a saturation pressure equal to 6.5 bars, gives place to an optimal flotation effectiveness. These results show the difficulties of treating worm water as emulsions oil-water, which requires the coupling of several processes to obtain a quality of rejection in conformity with the standard values.