Insights into the role of attapulgite clay on the efficient removal of microplastics by sand filters in various waters

Abstract

Plastics are extensively used in various fields and could be breakdown into small pieces as microplastics (MPs) and then be introduced into aquatic environments. MPs pollution pose serious threat to both ecosystems and humans via water-carrying pathways. The development of effective and efficient methods to remove MPs from aquatic systems is urgent. Sand filters is the unit which was commonly used to remove particulate contaminants from waters. Attapulgite (ATP) clay is a kind of minerals widely present in natural environments, with the virtues of excellent adsorption capacity. Herein, we used quartz sand filters with the addition of ATP for the efficient removal of MPs. Polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET, both of spheres and fragments) particles with sizes of ∼ 1 μm were used as representative MPs. Results showed that with the addition of ATP (100 mg L⁻¹) in 5 mg L⁻¹ MPs suspensions, the removal of all kinds of MPs reached to ∼ 100 %, with no passing out of MPs from sand filters as observed from the breakthrough curves (BTCs) in 10–100 mM NaCl and 1–10 mM CaCl₂ solutions. In addition, in real lake and river waters, the efficient removal was also obtained for PS and PP MPs with ATP, even with the lowest for removal PS MPs in lake water reaching as high as ∼ 35 %. The entanglement and vehicle effect induced by ATP was confirmed by its individual transport and also the MPs-ATP agglomerates formation verified via SEM, TEM, and DFT simulations. The results of this systematic and mechanistic study imply that sand filters modified with ATP might be a promising green remediation method to remove MPs from aqueous solutions in future.