Removal of microplastics or nanoplastics using nameko (Pholiota nameko) mucilage as a flocculant

Microplastics are widely distributed in aquatic environments, and there are concerns regarding their adverse effects on living organisms. Therefore, methods for their separation and removal from water are required. However, such technology has not yet been established. Pholiota nameko, commonly known as nameko, is an edible mushroom that secretes mucus composed mainly of pectin. In this study, it was demonstrated that a nameko mushroom mucilage solution (NMS) can act as a flocculant for microplastics and nanoplastics. For polystyrene microplastics (size: 1.0 μm), the suspension was mixed with NMS and Fe(III) for 20 s, resulting in the removal of 95.3% of the microplastics from the supernatant after 5 min. The separation of polystyrene microplastics from the water was achieved in a short time. Furthermore, when the washing wastewater of nameko was used as a flocculant for microplastic flocculation, the removal rate was 98.4%. Nanoplastics (polystyrene, size: 100 nm) were also sedimented by adding NMS and Fe(III). The removal rate (%) was 87.4%. Pectin in the NMS forms a gel with Fe(III). The zeta voltage of the microplastics is negative, and they interact with Fe(III) by Coulomb attraction. Consequently, flocs containing Fe(III), pectin, and plastic particles are formed. Microplastics and kaolin in the suspension were simultaneously flocculated and sedimented in the same manner. The rapid and highly efficient flocculation activity of NMS can be attributed to the large structure of pectin in the NMS. Based on these results, we concluded that NMS can be used as an efficient bio-flocculant for plastic particles.