Anaerobic Digestion of Bioplastic Packaging Materials

It has been estimated that 30 to 40% of food produced in the U.S. is never consumed by humans. Waste generated at the agricultural and food processing stages of the “farm-to-fork” spectrum is relatively homogeneous and of consistent quality, and thus is often suitable for secondary products such as animal feed. A far greater proportion of food waste is produced by households and consumer-facing businesses, and is generally more heterogeneous and often co-mingled with packaging materials. Therefore, packaging systems that are compatible with alternative end-of-life scenarios (e.g., composting, biodigestion) need to be developed. Anaerobic digestion (AD) has gained attention as a sustainable food waste conversion technology, because it converts biodegradable materials into methane-rich biogas and fertilizer. However, plastic packaging co-mingled with food scraps has to be separated before the AD process, even if the plastic is regarded as “biodegradable”, because the degradation timescale is much longer than the food material itself. If the biodegradation rate of bioplastics can more closely match that of the food waste, both materials can in principle be combined in a single stream for end-of-life upcycling. Polymers such as polylactic acid (PLA) have a diverse range of applications, but they take a prolonged period to degrade completely. On the contrary, thermoplastic starch and polyhydroxyalcanoate (PHA) stand out as fast degrading polymers that can be compounded into polylactic acid to improve biodegradation. Using an automated biomethane potential (BMP) measurement device, the anaerobic biodegradation of commercially available bioplastics was investigated under mesophilic and thermophilic conditions, and we also explored potential pathways for increasing biodegradation rates through use of additives and changes to the polymeric structure. Moreover, co-digestion of some bioplastics with food waste resulted in a measurable increase in biomethane generation, indicating a synergistic effect.