Estimation of Microplastic Emissions Caused by Moving Bed Biofilm Reactors (MBBRs)

Moving bed biofilm reactors (MBBRs) are well established for wastewater treatment. While BOD/COD removal is a typical application, MBBRs are also used for nitrogen elimination, as well as secondary and post-treatment. Due to the robustness of the biofilm, MBBRs are especially suitable for low water temperatures and for challenging conditions. Despite the many benefits of MBBRs, the potential for microplastic emissions caused by constant abrasion of the implemented carriers is often discussed. Direct measurements are not possible due to only minimal material loss in combination with great variations in initial carrier weight. Therefore, the influent and effluent of full-scale MBBRs for municipal wastewater were sampled and analysed for concentrations of polyethylene, polypropylene and styrene–butadiene rubber. Furthermore, different experiments were conducted in lab-scale reactors in order to gain data for an estimation of the actual material loss of the MBBR carriers. The results show that a material loss in the range of 101–102 µg/L can be observed but the microplastic concentrations caused by the MBBR carriers were negligible compared to the overall microplastic concentrations in the inflow of sampled wastewater treatment plants, which were in the range of 103–104 µg/L.