Removal of polyethylene micro(nano)plastics from water: Exploring the combination of anodic oxidation and membrane microfiltration

Micro- and nano-plastics (MNPs) have raised concerns regarding their potential ecological and human health impacts. Although these contaminants are not yet regulated under environmental legislation, international and European institutions are beginning to adopt directives to prevent their release through wastewater effluents. However, most existing treatment technologies are ineffective at removing MNPs. In this context, this study explores, for the first time, the use of anodic oxidation (AO) using an electrochemical flow-through cell equipped with commercial electrodes for the removal of polyethylene (PE) MNPs from water. Although limited removal was achieved (50 ± 5% at 15 mA cm −2 ), the primary benefit of the AO process was the physical agglomeration of the PE MNPs, which enhanced the efficiency of subsequent filtration using either a 5 µm cellulose acetate membrane (from 73 ± 2% to 85 ± 3% at 15 mA cm −2 ) or a 20 µm stainless steel grid (from 51 ± 2% to 78 ± 5% at 15 mA cm −2 ). A comprehensive characterisation of the PE agglomerates revealed that the AO process induced physicochemical changes at their surface. Although the molecular weight remained practically unchanged, the study of the GPC–IR measurements showed that chain scission may have occurred due to an increase in short-chain branches. The µ–FTIR spectra of the treated PE MNPs showed vibrational bands associated with oxygen-containing functional groups, potentially introduced during the AO process. Furthermore, NMR analysis revealed that oxidation products were confined to the surface of the PE MNPs.