Microplastics in real wastewater treatment schemes: Comparative assessment and relevant inhibition effects on anaerobic processes

Abstract

The occurrence, fate and removal of microplastics (MPs) in a wastewater treatment plant (WWTP) in Central Italy were investigated together with their potential adverse effects on anaerobic processes. In the influent of the WWTP, 3.6 MPs . L -1 were detected that mostly comprised polyester fibers and particles in the shape of films, ranging 0.1-0.5 mm and made of polyethylene and polypropylene (PP). The full-scale conventional activated sludge scheme removed 86% of MPs, with the main reduction in the primary and secondary settling. MPs particles bigger than 1 mm were not detected in the final effluent and some loss of polymers types were observed. In comparison, the pilot-scale upflow granular anaerobic sludge blanket (UASB) + anaerobic membrane bioreactor (AnMBR) configuration achieved 94% MPs removal with the abatement of 87% of fibers and 100% of particles. The results highlighted an accumulation phenomenon of MPs in the sludge and suggested the need to further investigate the effects of MPs on anaerobic processes. Accordingly, PP-MPs at concentrations from 5 PP-MPs . gTS -1 to 50 PP-MPs . gTS -1 were spiked in the pilot-scale UASB reactor that was fed with real municipal wastewater, where up to 58% decrease in methanogenic activity was observed at the exposure of 50 PP-MPs . gTS -1 . To the best of our knowledge, the presented results will be the first to report of PP-MPs inhibition on anaerobic processes.

Assessment of Microplastics in a Municipal Wastewater Treatment Plant With Tertiary Treatment: Removal Efficiencies and Loading Per Day Into the Environment

“…Several mechanisms have been proposed; i.e., a lower residence time for smaller MP than for larger plastic debris (Enders et al 2015), small MP fragment in much higher abundance than large ones (Wang et al 2018) and aggregation and settling into the sludge for the lowest sizes (van den Berg et al 2020). Furthermore, the MPs percentage smaller than 500 µm increased from the INF (18.63%) to the EFF (21.43%), after UV disinfection, similar to those results reported after chemical disinfection, with a degradation level depending on contact time, temperature, and disinfectant concentration (Dris et al 2015;Pittura et al 2021).…”

The Effect of Wastewater Treatment Plants on Retainment of Plastic Microparticles to Enhance Water Quality—A Review

“…However, MPs can have potential adverse effects on anaerobic processes, which normally yield biogas as a useful side-product. Thus, L. Pittura et al [142] have shown that in their case the presence 50 polypropylene MPs per g of solid led to a decrease of the methanogenic activity by 58%. This "poisoning" of the anaerobic microorganisms may be due to leachates from the MPs, which contain small organic molecules but also heavy metals.…”

“…These can be anaerobic digestion or aerobic digestion/composting. Here, L. Pittura et al have shown that 86% of MPs (which included 100% of the particles and 87% of the fibers) can be retained with a pilot scale upflow granular anaerobic sludge blanket (UASB) in combination with an anaerobic membrane bioreactor (AnMBr) [142]. However, MPs can have potential adverse effects on anaerobic processes, which normally yield biogas as a useful side-product.…”

“…Additionally, most studies have solely looked at MP concentrations in the WWTP influent and final effluent, but only few studies have investigated the MP concentrations at the different treatment stages[90] [117]. Nanoplastics (NPs) have also not been assessed thoroughly.Figure 2, possible set-up of a wastewater treatment plant (partially adopted from[142]). Nevertheless, it is clear that WWTPs cannot completely retain MPs, and that the effluent from WWTPs contributes to the MP load in receiving waters[83] [90] [93] [95] [99] [101] [102] [113] [114] [152].…”

Presencia y evolución de microplásticos en estaciones depuradoras de aguas residuales de la Región de Murcia: propuesta de las mejores tecnologías disponibles para una emisión cero

“…(Lenz et al, 2015). Por ejemplo, es muy común el uso de antioxidantes en polímeros tales como PP y PS (Pittura et al, 2021). El Anexo VI muestra los espectros de distintos MP aislados y sus polímeros de referencia.…”