Enhancing the performance of coagulants for wastewater treatment by varying and optimizing the experimental parameters

Abstract

This study is conducted to find the best suited operating conditions for the coagulation process both experimentally and analytically. Three coagulants: Aluminum sulphate, Ferric chloride and Ferric sulphate were used for the treatment and it was found that a dose of around 450 ppm of Ferric chloride performed the best compared to the other two coagulants tested for the wastewater since it can achieve a 95.72 % turbidity removal. For color, the dose was 300 ppm, which achieved an 88.77 % removal. Moreover, operating conditions such as agitation speed and pH were varied separately at optimum dose to find their effect on the coagulation process. It is found that Ferric chloride can perform most efficiently if the wastewater pH is kept above 7.0 and agitation speed is kept around 160 rpm. Afterwards, models were developed by Response Surface Methodology (RSM) analysis to describe the dependence of operating variables namely the dose, agitation speed and pH and to find their interactive effects on responses such as color and turbidity removal. It was found that the combined effect of dose and pH was influential in controlling the turbidity reduction whereas dose and agitation speed were found to affect the color removal of the effluent synergistically. It was found that an inverse square root model fits more closely compared to polynomial model based on statistical analysis; For the inverse square root model, R2turbidity=0.89 and R2color=0.90 were found which were significantly higher than the corresponding values for quadratic model. Later, the parameters were optimized using the developed model in which a dose of 208.21 ppm FeCl3 (≈208ppm), 197.91 rpm agitation speed (≈198rpm), and pH = 7.0 yielded the best responses. The models were further verified by experiments which provided an accuracy of about 80 % and 95 % in terms of turbidity and color removal respectively. Finally, a brief cost analysis for the coagulation process was performed which depicts that, RSM optimized condition can reduce the overall costs by almost 32 % compared to the batch optimized condition.