Abstract
Generation of microplastics (MPs), as a result of the increasing amount of plastic waste from human activities, is an emerging global concern that potentially threatens human health due to its intrinsic toxicity and ability to transfer pollutants. We examined the flocculation/coagulation for efficiently removing MPs (here, polyethylene (PE) and polyethylene terephthalate (PET)) in water by applying in-situ ferrate treatment, which exploits easy preparation and reduces toxic sludge production but has high coagulation efficiency. The PE and PET removal efficiency was evaluated by measuring the amounts of PE and PET in the as-treated supernatant using microscope equipped Fourier-transformed infrared spectroscopy. Overall, in-situ ferrate coagulation removed >80 % of PE and PET in a range of ∼0.9–3.6 mg/L of coagulant dose. In particular, >99 % of PE was removed with 2.7 mg/L coagulants, whereas PET removal efficiency reached 75 % at the highest dose (3.6 mg/L ferrate). However, the presence of organic humic acid (HA) significantly enhanced PET removal efficiency, reaching >99 % at the highest dose (3.6 mg/L ferrate). According to the mechanism study, HA remarkably promoted charge neutralization at low doses, corresponding to the zeta potential reaching zero. In particular, PE and PET exhibited different floc formations owing to ferrate coagulation. Ferrate closely and tightly adhered to the surface of PET, indicating that in-situ ferrate induced the adsorption of MPs. Based on the removal test and mechanism study, in-situ ferrate flocculation/coagulation processes are highly efficient for removing MPs in surface water containing low concentrations of natural organic matter. In the real surface natural water condition, >98 % of MPs removal efficiency was achieved by - twofold decreased ferrate dose (1.8 mg/L) without microfiltration membrane process.
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