Waste emulsion cutting oil has a very high COD (Chemical Oxygen Demand) and it was very harmful to the environment. In this study, flocculation method was investigated to reduce COD of the waste emulsion cutting oil discharged from Samsung, Thai-nguyen company. The waste emulsion cutting oil with the initial parameters such as oil content of 5.35%v/v; pH = 8.72; COD = 147,200 mg/l was used. Particle size and its distribution of the emulsion were determined by laser scattering. Results showed that the particle size of the emulsion has a narrow characteristic ranging from 0.058 to 1.729 µm, averaged at 0.22 µm. Several factors affecting to the flocculation process were pH (ranging from 3 to 10); Al2(SO4)3 content; C-PAM content and stirring speed during treatment of emulsion cutting oil. The best efficiency in COD reduction obtained was 98.24% (COD is 2,586 mg/l) at the optimum condition of pH = 5; Al2(SO4)3 of 2 g/l; C-PAM of 12 mg/kg at a stirring speed of 50 rpm for 25 minutes.
