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

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 im), 0.1 mm (100 im) 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 0.45�m. 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 �m and 119.5 �m for irregular plane microplastics and between 3 �m and 15 �m for spherical microplastics. The dimensions of microplastics in the form of fibers are also in the range of tens of �m 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.

The Effect of Ceramic Membranes’ Structure on the Oil and Ions Removal in Pre-Treatment of the Desalter Unit Wastewater

Salts, organic materials, and hazardous materials can be found regularly in the effluent from a desalter unit of crude oil. These materials should be separated from the wastewater. Four kinds of inexpensive and innovative ceramic microfiltration membranes (mullite, mullite-alumina (MA 50%), mullite-alumina-zeolite (MAZ 20%), and mullite-zeolite (MZ 40%)) were synthesized in this research using locally available inexpensive raw materials such as kaolin clay, natural zeolite, and alpha-alumina powders. Analyses carried out on the membranes include XRD, SEM, void fraction, the average diameter of the pores, and the ability to withstand mechanical stress. Effluent from the desalter unit was synthesized in the laboratory using the salts most present in the desalter wastewater (NaCl, MgCl2, and CaCl2) and crude oil. This synthesized wastewater was treated with prepared ceramic membranes. It was discovered that different salt concentrations (0, 5000, 25,000, 50,000, 75,000, and 100,000 mg L−1) affected the permeate flux (PF), oil rejection, and ion rejection by the membrane. Results showed that in a lower concentration of salts (5000 and 25,000 mg L−1), PF of all types of ceramic membranes was increased significantly, while in the higher concentration, PF declined due to polarization concentration and high fouling effects. Oil and ion rejection was increased slightly by increasing salt dosage in wastewater due to higher ionic strength. Monovalent (Na+) and multivalent (Ca2+ and Mg2+) ion rejection was reported about 5 to 13%, and 23 to 40% respectively. Oil rejection varied from 96.2 to 99.2%.

Cross-Linking Combined with Surfactant Bilayer Assembly Enhances the Hydrophilic and Antifouling Properties of PTFE Microfiltration Membranes

The inherent strong hydrophobicity of Polytetrafluoroetylene (PTFE) microfiltration membranes results in low separation efficiency and easy contamination. In order to enhance its hydrophilic and antifouling properties, we first modified the PTFE microfiltration membrane by using Polyethylene glycol laurate (PEGML) for first layer deposition and then used Polyvinyl alcohol (PVA)/citric acid (CA) cross-linked coatings for second layer deposition. The Scanning Electron Microscope (SEM) results showed that the fibers and nodes of the modified PTFE microfiltration membrane were coated with PVA/CA hydrophilic coating. FT-IR Spectromete and X-ray photoelectron spectrometer (XPS) analysis results confirmed that crosslinking of PVA and CA occurred and that PEGML and PVA/CA were successfully deposited onto the membrane surface. The modification conditions were optimized by hydrophilicity testing, and the best hydrophilicity of the modified membrane was achieved when the crosslinking content of PEGML was 2 g·L−1, PVA was 5 g·L−1, and CA was 2 g·L−1. PTFE microfiltration membranes modified by the optimal conditions achieved a water flux of 396.9 L·m−2·h−1 (three times that of the original membrane) at low operating pressures (0.05 MPa), and the contact angle decreased from 120° to 40°. Meanwhile, the modified PTFE microfiltration membrane has improved contamination resistance and good stability of the hydrophilic coating.