Combined Fenton-Type Oxidation and Anaerobic Digestion of Polyethylene to Methane Using Biochar Catalysts

Chemical recycling of polymers offers a route to valorize waste beyond mechanical recycling, which is increasingly inadequate to address global plastic production volumes. Low-density polyethylene (LDPE) is particularly challenging due to its chemical inertness and mechanical recycling limitations. We demonstrate a coupled metal-free Fenton-type oxidation with anaerobic digestion (AD) to convert LDPE to methane using biochar catalysts. Biochars derived from wood and grain, pyrolyzed at 300 and 700 °C, were characterized and evaluated as heterogeneous metal-free Fenton-type catalysts for oxidative degradation of LDPE to a mixture of mono- and dicarboxylic acids. Under reaction conditions of 180 °C, pH ≈ 7, 15% v/v H 2 O 2 and 10 wt % catalyst loading, we achieved 85% mass loss and a 54% acid yield. Biochar prepared at a lower pyrolysis temperature (300 °C) outperformed the 700 °C analogues, attributed to a higher surface oxygen functionality that mediates Fenton-like activity. The resulting acid mixture, which constitutes the liquid fraction obtained after vacuum filtration to remove solids (composed of the catalyst and any unreacted LDPE), was fed directly into AD, enabling biomethanation and subsequent methane production.