Microbial Recycling of Polylactic Acid Food Packaging Waste into Carboxylates via Hydrolysis and Mixed-Culture Fermentation

• Published in: Microorganisms (Basel) 2023-08, Vol.11 (8), p.2103
• Main Authors: Strik, David P. B. T. B., Heusschen, Brian
• Format: Article
• Language: English
• Subjects: Acetic acid; Aluminum; Anaerobic microorganisms; Bacteriology; Biodegradation; Biogas; bioplastic; Bioplastics; Broths; Carbon; Carboxylates; Carboxylation; Circular economy; Composting; Cultures and culture media; Elongation; Experiments; Fatty acids; Fermentation; Fermented food; Food; Food packaging; Food waste; Hydrolysis; Lactic acid; Lubricants; Methods; Microorganisms; Nutrients; pH control; PLA; Plastic debris; Plastics; Polylactic acid; pretreatment; Raw materials; Recycling; Waste management; Waste streams
• ISSN: 2076-2607; 2076-2607
• DOI: 10.3390/microorganisms11082103

To establish a circular economy, waste streams should be used as a resource to produce valuable products. Biodegradable plastic waste represents a potential feedstock to be microbially recycled via a carboxylate platform. Bioplastics such as polylactic acid food packaging waste (PLA-FPW) are theoretically suitable feedstocks for producing carboxylates. Once feasible, carboxylates such as acetate, n-butyrate, or n-caproate can be used for various applications like lubricants or building blocks for making new bioplastics. In this study, pieces of industrial compostable PLA-FPW material (at 30 or 60 g/L) were added to a watery medium with microbial growth nutrients. This broth was exposed to 70 °C for a pretreatment process to support the hydrolysis of PLA into lactic acid at a maximum rate of 3.0 g/L×d. After 21 days, the broths of the hydrolysis experiments were centrifugated and a part of the supernatant was extracted and prepared for anaerobic fermentation. The mixed microbial culture, originating from a food waste fermentation bioprocess, successfully fermented the hydrolyzed PLA into a spectrum of new C2-C6 multi-carbon carboxylates. n-butyrate was the major product for all fermentations and, on average, 6.5 g/L n-butyrate was obtained from 60 g/L PLA-FPW materials. The wide array of products were likely due to various microbial processes, including lactate conversion into acetate and propionate, as well as lactate-based chain elongation to produce medium-chain carboxylates. The fermentation process did not require pH control. Overall, we showed a proof-of-concept in using real bioplastic waste as feedstock to produce valuable C2-C6 carboxylates via microbial recycling.