We can't find the internet
Attempting to reconnect
Something went wrong!
Hang in there while we get back on track
Fate of microplastics in a centralized biogas plant treating mainly sewage sludge
Summary
Researchers tracked the fate of microplastics through a centralized biogas plant treating sewage sludge, examining how anaerobic digestion and subsequent dewatering partition microplastics between solid and liquid digestate fractions. The study informs efforts to develop safer digestate-based recycled fertilizers that minimize microplastic introduction to agricultural soils, where 20-55% of microplastics entering wastewater treatment plants are estimated to end up in sludge.
According to estimates, 20-55 % of microplastics entering wastewater treatment plants is entrapped in sewage sludge. Sewage sludge is often treated by anaerobic digestion in Europe, either in biogas plants directly connected to the wastewater treatment plants, or in centralized biogas plants receiving sludge from multiple sources. The anaerobic digestion is typically followed by dewatering of the digestate, producing solid and liquid fractions. The solid fraction of digestate, particularly, is often recycled to agricultural land due to its high nutrient content, thus introducing also microplastics to soil. In order to develop safer digestate-based recycled fertilizers, it is important to understand the behavior and fate of microplastics across the anaerobic digestion and the subsequent solid-liquid separation process. In this study, we examined the abundance and flow of microplastics (>20 μm) at a centralized biogas plant receiving mainly sewage sludge. Over 99 % of microplastics and over 90 % of phosphorus were retained in the solid fraction of digestate after the dewatering, further emphasizing the need to find new methods to manage sewage sludge (digestate) to enable the safe recycling of nutrients according to the circular economy principles. Polystyrene microbeads of unidentified source composed 65 % of microplastics detected in the solid fraction, indicating that local sludge origins may have a significant impact on the occurrence and types of microplastics observed at centralized biogas plants. The liquid fraction of digestate carried less than 1 % of microplastics and over two-thirds of nitrogen, proposing the potential of this fraction as a cleaner source of nitrogen for recycling.
Sign in to start a discussion.
More Papers Like This
Configuration-driven microplastic fate in full-scale sewage sludge treatment and opportunities for system-level mitigation
Researchers examined how different treatment configurations in wastewater plants shape the types and concentrations of microplastics that end up in sewage sludge — the solid byproduct that is frequently spread on agricultural land as fertilizer. Microplastic concentrations in final sludge ranged from 617 to 936 particles per gram of dry solids, with fine fragments under 100 micrometers dominating, and the specific sequence of thickening, digestion, and dewatering steps significantly influenced which polymer types were retained. Since sludge application is a major route for microplastics to enter farmland, optimizing treatment processes could meaningfully reduce environmental contamination.
Fate of microplastics in sewage sludge and in agricultural soils
Researchers reviewed how microplastics accumulate in sewage sludge at wastewater treatment plants and then spread into agricultural soils when that sludge is applied as fertilizer, finding that sludge treatment processes can alter microplastic size and shape but do not eliminate them. The review calls for standardized methods to study how different sludge treatments affect microplastic properties and their downstream risks to soil health.
The occurrence and fate of microplastics in a mesophilic anaerobic digester receiving sewage sludge, grease, and fatty slurries
Researchers analyzed microplastic loads entering and leaving a mesophilic anaerobic digester at a wastewater treatment plant serving nearly 800,000 people. They found that the digester received approximately 7,326 kg of microplastics per year, with digested sludge containing about 30% less, though this reduction was within the variability of the measurements. The study provides important data on the fate of microplastics during sewage sludge treatment processes.
Systematic study of microplastics on methane production in anaerobic digestion: Performance and microbial response
Microplastics are increasingly found in wastewater treatment systems, and this study systematically examined how different types, concentrations, and sizes of microplastics affect the anaerobic digestion process used to break down sewage sludge and generate biogas. Polyethylene microplastics were found to inhibit methane production, with finer particles and higher concentrations causing greater disruption to the microbial communities driving digestion. The findings matter because microplastics in sewage sludge can impair the treatment process and also end up spread on agricultural land when sludge is used as fertilizer.
A method for the characterisation of microplastics in sludge
Researchers developed a method for detecting and characterizing microplastics in sewage sludge, which concentrates the majority of microplastics removed during wastewater treatment. This method is important because sludge is widely spread on agricultural land, making it a key pathway for microplastics entering soils.