Effect of process-based strategies on anaerobic digestion of 3D-printing-derived polylactic acid: biogas production and mechanistic interpretation

The rapid growth of 3D printing technology has led to an increase in polymeric waste, which requires proper management to avoid further pressure on the end-of-waste system. In this context, anaerobic digestion (AD) is a promising strategy for biorenewable energy production (e.g., biomethane) when biodegradable polymers, such as polylactic acid (PLA), are employed. Indeed, the latter has been widely used as a bioactive polymer for 3D printing, but the high printing temperatures can alter its properties, thereby affecting its biodegradability. This study investigated, for the first time, the biodegradation of 3D-printing PLA waste via AD under mesophilic conditions for 63 days. With the aim of improving the biodegradability of 3D-printing-derived waste, various process-based strategies, including micro-aeration, Fenton oxidation, and thermo-alkaline pretreatment, were thus employed. Biogas production and speciation during AD, as well as weight loss of PLA samples (i.e., untreated, unprinted, and printed), and their further characterization through differential scanning calorimetry analysis, FT-IR spectroscopy, and viscometrical measurements were assessed to study the effectiveness of the investigated process-based strategy. The combined thermo-alkaline pretreatment (i.e., 2.5 %w/v of Ca(OH)2 at 70 °C for 72 h) applied on 3D-printed PLA samples resulted in a total weight loss of 83.1% after AD process and a biomethane yield of approximately 360 mL/gPLA, which were significantly higher than that achieved with the control samples (i.e., 30% and <100 mL/gPLA, respectively). These results provided practical insights for the integration of additive manufacturing waste into AD-based circular economy strategies.