Effect of microplastic ingredient on the removal of microplastics by calcium alginate flocculation

Abstract

The widespread presence of microplastics induce a serious threat to the survival of living organisms. Herein, calcium alginate hydrogel was selected as a flocculant to remove microplastics from water. To determine the variability of the flocculation method for the removal of microplastics with different properties, 11 microplastics of different sizes or components were used. The results showed the removal of different microplastics were 99.5% (PSMP 5 µm), 99.5% (24 h aged PSMP), 98.6% (72 h aged PSMP), 97.1% (48 h aged PSMP), 92.0% (PMMA 15 µm), 84.0% (PAMP 5 µm), 82.0% (PVCMP 1 µm), 80.2% (PLAMP 500 mesh), 68.0% (PEMP 100 mesh), 52.0% (PE 20 µm), and 52.0% (PP 1000 mesh). Microplastics were mainly wrapped and swept by flocs. The density and surface hydrophilicity of microplastics are the main reasons for the discrepancy in their removal efficiency. Calcium alginate also performed well in the removal of microplastics in natural water. When the initial concentration of the polystyrene microplastic suspension was 5 mg/L, the removal rates of microplastics in the five water samples were 99.60% (pipe water), 98.19% (lake water), 98.71% (river water), 100.44% (sludge supernatant), and 100.00% (seawater). Also, flocculation method could almost completely remove fibrous microplastics from washing wastewater. It is aim to provide reference data for the removal of different microplastics in water by flocculation, and also expect to increase the emphasis on microplastic variability in the future removal exploration.