Microplastics affect the removal of dye in textile wastewater: Adsorption capacity and its effect on coagulation behavior

Microplastics (MPs) are easily prone to adsorption reactions in an aquatic environment. Dyes in textile wastewater might be released and adsorbed by microplastics, causing ecological pollution. In this paper, polyamide microplastics (PA MPs) and reactive orange dye (KGN) were used as the main research objects, the adsorption capacity of different MPs, the adsorption mechanisms of KGN on PA MPs, and the effect of microplastic adsorption on the coagulation process were investigated. PA MPs had a maximum adsorption capacity of 0.866 mg/g. The kinetic results demonstrated that chemisorption, which can be broken down into three stages: membrane diffusion, intraparticle diffusion, and dynamic equilibrium, was primarily responsible for controlling the adsorption process. Adsorption took place on the surface of the monomolecular layer, according to the isotherm modeling, which indicated that the adsorption results were more consistent with the Langmuir isotherm. In addition, the effect of microplastic adsorption followed by coagulation experiments was investigated. When reactive orange is adsorbed by PA MPs, the maximum increase in coagulation removal efficiency is 4.7 %, it can also improve the growth ability of flocs, enhance the uniformity, and make their average particle size close to 63 μm. Finally, the possible mechanisms of adsorption and coagulation during the experiments are described, and an outlook for future work is given.