The utilization of galactomannan from spent coffee grounds as a coagulant aid for treatment of synthetic Congo red wastewater

There has recently been a significant growth in research exploring natural-based coagulant due to its various benefits to decrease or even substitute inorganic chemical coagulants. Due to their abundance, polysaccharide-based coagulant and coagulant aid are promising sources. This study reports the utilization of galactomannan extracted from spent coffee grounds as a natural coagulant aid in coagulation of Congo red synthetic wastewater. Galactomannan was extracted using water and separated by adding ethanol. The obtained galactomannan powder was subsequently characterized. The coagulation study was conducted by using the standard jar test apparatus at a fixed dosage of FeCl3 (160 mg/L) and a pH of 6. The effect of galactomannan as a coagulant aid was observed by varying the galactomannan dosage and Congo red concentration. This revealed that galactomannan as a coagulant aid could increase the removal of Congo red, amounting to a 30-90% removal, depending on the Congo red concentration, compared to using FeCl3 only (0-65%). The coagulation adsorption study was also investigated using several isotherm models. This showed that the Congo red coagulation using FeCl3 only followed the Langmuir isotherm, indicating the monolayer-homogeneous formation during the coagulation. With the presence of galactomannan the coagulation was best described by the Brunauer-Emmett-Teller isotherm, indicating multilayer-heterogeneous adsorption, possibly due to interparticle bridging of galactomannan during colloid aggregation. The findings suggest the synergistic effect of galactomannan and FeCl3 in the coagulation process as well as the proved potential of galactomannan from spent coffee grounds as a natural coagulant aid.