Abstract:
The aim of this research was to study the treatment of wastewater containing cutting oil and algae by the combining process of Dissolved Air Floatation (DAF) and coagulation, which was denoted as the Modified Dissolved Air Flotation (MDAF). It was found that the treatment efficiencies were affected by the wastewater types in terms of coagulation process required and the A/S ratio, and the fluid dynamic parameters (i.e. G.T and OFR values). From this study, the optimal G.T and OFR values were 5,500 s/s and 0.15 0.25 m/min, respectively. The treatment efficiency of the cutting oil wastewater by MDAF process in this condition was 82% with the coagulant (alum) dosage of 100 mg-alum/1 g-oil. The A/S ratio in the range of 0.024 0.052 g-air/g-oil was obtained. Moreover, the treatment efficiencies of DAF and MDAF processes were relatively closed at 65% and 45% for the wastewater containing algae with 10 and 15 day cell age, respectively. In this case, the ratio of alum to cell numbers was 15 mg-alum/10⁹ cells with the A/S ratio of 0.053 g-air/10⁹ cells. Furthermore, from the mathematical model application, the adsorption isotherm model provided the advantages on the filtration efficiency equation for predicting of treatment efficiency and describing the occurred mechanisms. In addition, the contact between cutting oil droplets and bubbles can be described by the Langmuir isotherm model. The A/∆S obtained from the isotherm model was in the range of 0.028 0.033 g-air/g-oil, which was similar to the experimental results.