Application of Response Surface Methodology (RSM) to Optimize Coagulation- occulation Process for Treatment of Metal Working Fluids Using Calcium Chloride and Ferric Sulfate

Objectives The current study aimed at optimizing the coagulation-flocculation process to treat metal working fluids (MVF) by calcium chloride and ferric sulfate using response surface methodology (RSM).
Methods The removal efficiencies of chemical oxygen demand (COD), turbidity, and the amount of released oil via coagulation process using calcium chloride and ferric sulfate as coagulants were studied. Central Composite Design (CCD) and RSM were used to optimize the operating variables including coagulant dosage and pH. Quadratic models were developed for the 3 responses of COD, turbidity, and released oil from MWF.
Results The results of the current study indicated that the optimum conditions were calcium chloride dosage of 4 g/L at pH 3.5. The COD, turbidity removal efficiency, and oil releasing from MWF were 93%, 96.9%, and 31.8 mL, respectively and the level of desirability was 91.2%. Optimum condition for ferric sulfate was 6.5 g/L at pH 4.5. The COD, turbidity removal efficiency, and oil releasing from MWF were 62.1%, 93.6% and 13.7 mL, respectively and the level of desirability was 91%.
Conclusion Coagulation-flocculation process using calcium chloride, compared with conventional coagulants such as ferric sulfate, was very effective on pollutants removal. Calcium chloride usage was 35% less than common coagulant while removal efficiency was greater.