Coagulation/flocculation process for marble processing plant effluent: Modelling and optimization through response surface methodology

Abstract

In this study, the coagulation-flocculation of a wastewater discharged from a marble processing plant was statistically analyzed and optimized. To make a systematic investigation on the coagulation-flocculation of the highly turbid wastewater (>1000 NTU), the response surface methodology was used to estimate a capable quadratic model with R-squared value of 98.84%. According to this model, the most critical parameter was the suspension pH with a p-value < 0.0001. Furthermore, the PEO-flocculant was proven as a substantial agglomerating reagent specifically at pH 12. On the other hand, no significant turbidity removal was observed upon the addition of the Fe-coagulant. When the experimental parameters of the coagulation-flocculation were optimized, it was found out that the minimum supernatant turbidity value of 3.81 NTU can be achieved by using the minimum amount of the Fe-coagulant:50 mg/l, and the maximum amount of the PEO-flocculant of 1.5 ppm at pH 11.5-12.0. In conclusion, it was proved that the significance of the calcium dissolved from the marble particles was greater than the Fe-coagulant in this process. The hydrolyzed calcium (CaOH+) species established a chemical bridge between the particle and the polymer and, as a result, enhanced the performance of the flocculation at the alkaline pH values.