Enhancing the coagulation process for the removal of microplastics from water by anionic polyacrylamide and natural-based Moringa oleifera

The existence of microplastics (MPs) in water is a significant global concern since they have the potential to pose a threat to human health. Therefore, there is a need to develop a sustainable treatment technology for MPs removal, as the conventional methods are inadequate to address this problem. Coagulation is a typical process in treatment plants that can capture MPs before releasing them into the environment. In this work, the removal behaviors of polyamide (PA), polystyrene (PS), and polyethylene (PE) MPs were systematically investigated through coagulation processes using aluminum sulfate (Al(SO)) and Moringa oleifera (MO) seeds extract. Subsequently, the coagulation performance of Al(SO) was improved by the separate addition of anionic polyacrylamide (APAM) and naturally derived MO. Results showed that Al(SO) in combination with APAM had better performance than Al(SO) or MO alone. In the Al(SO)+APAM system, the removal efficiencies were 93.47%, 81.25%, and 29.48% for PA, PS, and PE MPs, respectively. Furthermore, the effectiveness of the Al(SO) and MO blended system was approximately similar to the Al(SO)+APAM system. However, the required amount of Al(SO) was decreased to 50% in the Al(SO)+MO system compared to the optimal dosage in the Al(SO) system alone. The combination of 40 mg/L of Al(SO) and 60 mg/L of MO resulted in removal efficiencies of 92.99%, 80.48%, and 28.94% for PA, PS, and PE MPs, respectively. The high efficacy of these enhanced methods was due to the synergic effects of charge neutralization and agglomeration adsorption, which were validated through zeta potential assessments and visual analysis using scanning electron microscopy (SEM) images. In the case of experimental conditions, initial pH had little impact on removal efficiency, while NaCl salinity and stirring speed directly affected MPs removal. Consequently, this research took a step toward finding a green strategy to remove MPs from water systems.