Abstract:
Cutting oil is widely used in various manufacturing industries as lubricant, coolant and among machining processes. After used, cutting oil wastewater has high COD, turbidity and suspended solids. It also contains surfactant, therefore causing emulsion in wastewater that is very stable and difficult to be treated effectively by conventional treatment processes. This research focused on efficiency and optimum conditions for low and high synthetic cutting oil wastewater treatment by Fenton and photo-Fenton processes. All experiments were controlled pH at 3.0 ± 0.2 and Ferrous sulfate (FeSO4.7H2O) was used as a ferrous ion source. The initial cutting oil concentrations were 0.1, 1.0, 4.0, 9.0 and 22.0 g.L-1. The results from the study showed that Fenton process indicated COD removal efficiency of 88.97% ± 5.63% and 91.98% ± 1.68% for 0.1 and 1.0 g.L-1 cutting oil concentrations, respectively with 50 mg.L-1 Fe2+ concentration and the mass ratio of Fe2+/H2O2 at 1: 2.5. At the Fe2+/H2O2 ratio of 1: 10, the highest COD removal efficiencies in photo-Fenton process were 96.21% ± 5.23% and 91.95% ± 1.52% for 0.1 and 1.0 g.L-1 cutting oil concentrations, respectively. For 4.0, 9.0 and 22.0 g.L-1 cutting oil concentration, the results showed that the COD removal was more than 87% at the optimal condition. The optimum chemical reagents for 4.0, 9.0 and 22.0 g.L-1 cutting oil concentrations were as the following Fe2+ = 75, 150, 300 mg.L-1 and H2O2 = 375, 300, 1500 mg.L-1. The efficiency of COD removal of Fenton and photo-Fenton were not significantly different (at confidence level 95%). As the emulsified oily wastewater used in the study had high turbidity, so turbidity of wastewater might hinder the absorption of UV light during the photo-Fenton process. Therefore, UV light did not enhance the reaction in photo-Fenton process. For the reuse of ferric sludge as an iron source in Fenton and photo-Fenton process, it was found that ferric sludge was able to be reused two times. Only a few cycles of sludge recycling was feasible because the accumulation of the remaining oil particles in the sludge from the previous cycle increased the oil particle concentration and organic contents in the sludge. In each cycle, COD removal from reused sludge became lower than previous cycle due to limited oxidant availability and high oil particle accumulation.