Organics Recycling Tradeoffs: Biogas Potential and Microplastic Content of Mechanically Depackaged Food Waste

Mechanical depackagers separate valuable organics from residual food packaging, creating new opportunities to recover energy (i.e., biogas) and nutrients (i.e., digestate) via anaerobic digestion (AD). However, the possibility of imperfect separation has raised concerns that digestate derived from depackaged food waste may contain microplastics (plastic particles <5 mm). To better understand this tradeoff, we evaluated biochemical methane potential (BMP) and other key AD parameters as well as plastic (0.5–1, 1–5, and >5 mm) content of two mechanically depackaged food waste streams and a derived digestate. The depackaged pre- and post-consumer organics had BMPs of 453 ± 52 and 435 ± 37 NmL CH4 g–1 VS, respectively, indicating substantial potential for energy recovery via AD. However, plastic was found in both depackaged waste streams (0.19 ± 0.13 and 0.062 ± 0.05% w/w, respectively, for pre- and post-consumer) and the derived digestate (0.018 ± 0.019% w/w). While low on a mass basis, plastic contamination could limit digestate reuse options, potentially undercutting the environmental benefits of AD. Further work is needed to standardize methods for measuring the plastic content in organic residuals and to evaluate the life cycle costs and benefits of using mechanical depackaging to increase food waste diversion to AD.