A novel gravity-driven dynamic membrane filtration reactor for microplastic removal from plastic recycling facility wastewater

Abstract

One of the most important point sources of microplastics (MPs) in water resources is plastic recycling facilities (PRFs). In this study, a novel gravity-driven (GD) dynamic membrane filtration (DMF) reactor was designed. The MP removal efficiency and mechanism were investigated for real PRF wastewater by using i) direct filtration (control), ii) pre-coating with wastewater treatment plant (WWTP) sludge, and iii) co-filtration with WWTP sludge. For this purpose, stainless steel meshes (100, 200, and 300 mu m) were used as dynamic membrane (DM) support material to investigate flux profiles, MP removals, and DM formation mechanisms. Visual inspection (scanning electron microscope and light microscope) of the support material and the DM layer was also analyzed. The average number of MPs in PRF of the feed was 12,835 +/- 6218 MP/L. Results showed that mass removal rates of MPs reached more than 99.5 % in each size of the support materials, which is comparable with polymeric membranes. The MPs removal efficiencies by number ranged between 68.3 % and 99.0 % in all meshes. It was determined that the DM layer formation on support meshes was also contributed by MP fiber networks, resulting in higher removal rates of MP fibers compared to fragment MPs. According to the obtained results, the GD-DMF system is a promising process for the treatment of wastewater highly loaded with MPs and is a significant low- carbon alternative to conventional membrane processes.