Synergistic effect of calcium chloride as coagulant and (chitosan-graft-polyacrylamide) as flocculant for anionic dyes removal from wastewater

In this study, the coagulation–flocculation technique was used to achieve high removal ratio of organic anionic pollutants (taking methyl orange (MO) dye as a model) from highly polluted wastewater, 1000 ppm. To this end, chitosan grafted polyacrylamide (Ch-g-PAM) was synthesized using both radical initiator H₂O₂ and microwave (MW) irradiation to accomplish the grafting reaction. Ch-g-PAM was used as a flocculation agent, while calcium ions were used as a coagulation agent. The grafting ratio was 400%. The prepared Ch-g-PAM was characterized by Fourier-transform infrared (FTIR) spectroscopy and X-ray diffractometry (XRD). The effects of reaction parameters on graft polymerization were studied, which were chitosan/acrylamide ratio, MW power, time of polymerization, and chitosan molecular weight. The effects of coagulant and flocculant concentrations, pH of the medium, and the initial dye concentration on the dye removal ratio were studied. The results showed a correlation between dye removal ratio and dye concentration, which indicates that the coagulation–flocculation technique is an effective pretreatment technique to remediate wastewater. Contaminated water with a concentration of MO dye as high as 1000 ppm was treated, with a removal ratio of 87.26% (i.e., 1 g of flocculant removes about 47 g of MO dye from its 1000 ppm solution).