Characterisation of Microplastics from the Effluent of a Municipal Wastewater Treatment Plant and from its Natural Receptor

Abstract

Results obtained from the characterization of three water samples (one representing the effluent of a municipal treatment plant and the two others representing surface water from the Jiu River/Romania, upstream and downstream of the effluent discharge point) are presented in this study in terms of microplastic content. The water samples were processed by successively passing them through a series of filters with the following dimensions: 5 mm, 0.5 mm (500 μm), 0.1 mm (100 μm) and then through some microfiltration membranes (MF) type EZ-Pak Membrane Filters (Merk-Millipore) made of a mixture of cellulose esters, with an average pore diameter of 0.45µm. In order to highlight the microplastics in the water samples, their analysis was performed as well as the solid material retained on the microfiltration membranes, by scanning electron microscopy (SEM) using a SEM Quanta FEG 250/Thermo Fischer Scientific. The results obtained highlighted the existence of microplastics in all the analyzed samples, in the known forms presented in the specialized literature: irregular planes, fibers and spheres. Their dimensions are variable, ranging between 3.2 µm and 119.5 µm for irregular plane microplastics and between 3 µm and 15 µm for spherical microplastics. The dimensions of microplastics in the form of fibers are also in the range of tens of µm and cannot be established exactly because in most cases they appear in the form of conglomerates. The treatment plant’s microplastic effluents content led to the modification of the physical-chemical indicators of the water in their natural receptor. Thus, the content of organic matter and total suspended matter in the downstream water compared to the effluent discharge point is higher than in the upstream water. The analysis of microplastics by SEM allows only their highlighting and their geometry, being a first step in the study of the pollution induced by such materials.