Microplastic Removal from Urban Wastewater: A Study on the Efficiency of Treatment Plants
Global plastic production has increased significantly in recent decades, leading to growing concerns about plastic waste. One particularly urgent environmental issue is the spread of micro- and nano—plastic particles smaller than 5 mm that originate from the breakdown of plastic products or waste. In addition to posing risks to the environment and human health due to their persistence, these particles can also carry pathogens or release other pollutants. In urban settings, their presence in wastewater is primarily linked to domestic discharges and surface runoff. Since this water is treated in wastewater treatment plants (WWTPs), it is crucial to assess whether current treatment stages are sufficient to remove microplastics.
This was the goal of a new study conducted in collaboration between the University of Trento, the University of Florence, Eco Research, and Eco Center. The research was carried out at a local WWTP and monitored the quantity and type of microplastics (10–5000 μm) at various treatment stages, using three complementary analytical techniques: FTIR spectroscopy, LDIR spectroscopy, and TD-GC/MS.
The results show that WWTPs can remove over 96% of the microplastics from wastewater, although they tend to concentrate in sewage sludge. Since this sludge may be reused in agriculture as fertilizer, it becomes a potential source of microplastic release into the environment. Therefore, targeted strategies are necessary for sustainable sludge management and reuse. For instance, including additional treatment steps such as sludge incineration or pyrolysis could prevent microplastics from being reintroduced into the environment.
A B S T R A C T
This study investigated microplastics (MPs) sized 10–5000 µm across stages of a conventional municipal wastewater treatment plant using multiple analytical techniques. Samples were collected via pumping and filtration, treated with the Fenton reaction for wet peroxidation, and separated by density separation. Analysis employed Focal Plane Array Micro-Fourier Transform Infrared Spectroscopy (FPA micro-FTIR), a widely used technique in MPs analysis, alongside the less common Laser Direct Infrared Spectroscopy (LDIR), providing complementary data on particle composition, shape, size, and colour. To enhance insights, spectroscopic methods were supplemented with Thermal Desorption Gas Chromatography-Mass Spectrometry (TD-GC/MS), calibrated for specific polymers, to quantify MPs by mass and assess removal efficiency. Wastewater treatment effectively reduced MPs. In influent samples, concentrations reached 72 MPs/L (FTIR), 2117 MPs/L (LDIR), and 177 µg/L (TD-GC/MS). Primary treatments removed 41 %–55 %, while the wastewater treatment plant effluent contained 1 MPs/L (FTIR), 93 MPs/L (LDIR), and 2 µg/L (TD-GC/MS), reflecting 96 %–99 % removal efficiency. Activated sludge showed concentrations of 123 MPs/L (FTIR), 10,800 MPs/L (LDIR), and 0.3 mg/g dry weight (TD-GC/MS), underscoring its role in MPs capture. However, sludge dewatering released significant MPs into centrifuge rejected water: 484 MPs/L (FTIR), 23,000 MPs/L (LDIR), and 1100 µg/L (TD-GC/MS). These results highlight the effectiveness of conventional treatments in MPs removal and the critical role of sludge in capturing these contaminants. However, sludge dewatering poses a risk of reintroducing MPs into the environment. Effective sludge management should prioritize nutrient recovery and biomass valorisation to mitigate these risks and minimise harmful environmental impacts.