Characterization of microplastic in anaerobic digestate

Associated manuscript is available here: doi: 10.3389/fsufs.2025.1666814<br>Microplastics (MP) have emerged as a contaminant of concern in the food system, introduced through food processing and packaging—and even detected in food products themselves. In efforts to reduce food system resource loss, food waste is being redirected from landfills toward circular solutions such as anaerobic digestion (AD). AD offers environmental benefits by converting organic waste into renewable biogas and nutrient-rich digestate. However, MP present in food waste can persist through this process, potentially contaminating the digestate. When applied to soil as fertilizer, this contamination may affect soil function and contribute to broader environmental pollution in agricultural and aquatic systems. This study investigates the abundance and characterization of MPs in the liquid digestate from an AD system co-digesting food waste and dairy manure. Using a novel microplastic extraction method involving wet peroxide oxidation and an EDTA-Triton X-100 solution to remove the organic matrix, MPs were isolated and analyzed for polymer composition and morphology. Results indicate that MPs are present in liquid digestate, with polyethylene terephthalate (PET) fibers as the dominant polymer type. These findings highlight the potential for AD to serve as a pathway for MPs to enter agricultural soils when digestate is land-applied as a fertilizer, raising concerns about long-term environmental impacts. Understanding the fate and characteristics of MPs in digestate is critical for evaluating AD’s role in sustainable waste management and developing strategies to mitigate microplastic contamination in organic waste recycling systems.