Optimization of coagulation-flocculation process conditions using the central composite design for pretreatment of Moroccan landfill leachate

In this article, we used response surface methodology to determine the best conditions for leachate treatment using coagulation-flocculation (CF) with calcium hydroxide (Ca(OH)(2)). The leachate is collected in a public landfill of the Fez City in Morocco. Hence, the central composite design was employed to optimise the values of the input parameters, namely pH, calcium hydroxide (CH) concentration, fast stirring time and slow stirring time. Additionally, turbidity, absorbance and sludge volume, which all characterize the leachate treatment efficiency, are considered in this study as the PCC design responses. Using the investigated quadratic model, we were able to establish a perfect relationship between these responses and the four input parameters. In fact, the results of the analysis of variances (p-value < 0.05) show that the four factors, including CH quantity and pH, have a significant impact on the three responses. Moreover, with the help of the desirability function and the isoresponse curves, we succeeded in obtaining the optimal values for pH, CH Concentration and the two stirring times (speed and slow) of 11.5, 13 g L-1, 25 and 11.5 min, respectively. With the use of such optimal conditions allowed, in a control test, for a reliable and efficient pollutant elimination, as measured by turbidity, absorbance reduction at 254 nm, and sludge volume after treatment of the order of 12 NTU, 80%, and 48 ml L-1, respectively.