Simultaneous optimization of multiple performance characteristics in coagulation-flocculation process for Indian paper industry wastewater.

The goal of this study was to optimize the coagulation-flocculation process in wastewater generated from the paper and pulp industry using a grey relational analysis (GRA)-based Taguchi method. Process parameters included types and doses of natural coagulants and coagulant aid, and pH. To track the efficiency of the treatment process, the following responses were chosen for optimization: chemical oxygen demand (COD), total dissolved solids (TDS) and turbidity of wastewater, alone or in combination or all together. Analysis of variance showed that the type and dose of the coagulant aid were the most significant parameters, followed by pH and the dose of the coagulant; the type of coagulant used was found to be insignificant in the coagulation-flocculation process. Optimization of process parameters to achieve lower turbidity and greater removal of COD and TDS was verified in a separate confirmatory experiment, which showed improvements in COD and TDS removal and a decrease in turbidity of 8.2, 6.35 and 26.17%, respectively, with the application of the Taguchi method and GRA.