Design of experiments for Malachite Green dye removal from wastewater using thermolysis – coagulation–flocculation

Thermolysis -coagulation-fl occulation was used for reduction of colour and chemical oxygen demand (COD) of aqueous basic dye Malachite Green.Statistical design of experiment was used for thermolysis experiments which resulted of 69.57% and 70.59% maximum reduction of COD and color, respectively at the optimum conditions of 95 min treatment time, 82°C treatment temperature, and pH 11.02.MgCl 2 was used as coagulant for coagulation-fl occulation.About 98% of color and 90% of COD were reduced at a fi nal pH of 10.89 and a coagulant dose of 3 g MgCl 2 l -1 of dye solution.The optimum conditions for coagulation-fl occulation process were determined by varying a single factor while keeping other factors fi xed at a specifi c set of conditions.Coagulation-fl occulation after thermolysis at the optimal operating conditions resulted in a reduction of 91.26% COD and 98.78% color at fi nal pH 10.89 but at a much lesser coagulant dosage of 500 mg l -1 .Compared to only coagulation-fl occulation, combined process of thermolysis followed by coagulation-fl occulation produced relatively less fl oc, since lesser amount of coagulant was required to remove higher color and COD.