Analysis of the potential role of microplastics as transporters of microorganisms in activated sludge

The presence of plastic microbeads in wastewater is a threat. Understanding their properties, as well as their potential to form biofilms, is of great importance to the efficiency of wastewater treatment plant operations. Moreover, plastic microbeads can provide a unique habitat for microbial biofilms, as a biospecific and active matrix attached to cell surfaces. In this study, we investigated the ability of microorganisms present in activated sludge to settle on different types of microplastics (polyethylene terephthalate, polyethylene, polypropylene). Biofilm formation was determined by measuring optical density and confirmed by microscopic observations. In addition, the microbial community was quantified throughout the experiment. The results showed that polyethylene had the highest affinity for coliform bacteria. In contrast, the same bacteria on polypropylene formed a biofilm at a relatively slow rate, which could result in high concentrations for a longer period of time. Mesophilic bacteria show moderate growth on polyethylene and polyethylene terephthalate. On the other hand, they show the lowest biofilm concentrations among polypropylene. For psychrophilic bacteria, all tested materials show relatively high affinity for biofilm formation. Differences in biofilm formation on the surfaces of different polymeric materials may be due to chemical and physical interactions.