Removal of methylene blue (basic dye) by coagulation-flocculation with biomaterials (bentonite and Opuntia ficus indica)

The use of conventional chemical coagulants and flocculants to treat pollutant-laden effluents generates residues with harmful effects on the environment. This has led us to think through this study of their replacement by more ecological natural products. The present work focuses on the use of a bentonite-based coagulant and a cactus-based flocculant (Opuntia ficus indica (OFIP)) in the elimination of a methylene blue (MB), a basic textile dye. The biomaterials are characterized by FTIR, XRD, SEM and pHPZC. To estimate the performance of the biomaterials in the coagulation-flocculation process, jar-test work was performed on the MB dye in aqueous solution. The monitoring of the variation of MB removal rates was performed by UV–visible spectroscopy. The effect of biomaterial masses, stirring time and speed and settling time on the dye removal process were studied. In addition, the effects of pH and initial MB concentration were also studied. The results show that a mass of 0.9 g of bentonite and 0.4 g of OFIP are the optimal quantities, giving a dye removal rate of 98.29 % during 19 min, at a stirring speed of 180 rpm and 40 rpm for coagulation and flocculation, respectively. These optimum values are obtained with a settling time of 15 min. However, pH does not have a significant influence on the MB removal rates. These biomaterials gave excellent results with 98.99 % dye removal rates at an initial MB concentration of 90 mg/L. In addition, for the purpose of testing the performance of the biomaterials, a comparative study using conventional chemicals was performed.