Development of a plastic waste treatment process by combining deep eutectic solvent (DES) pretreatment and bioaugmentation with a plastic-degrading bacterial consortium.

Polyethylene terephthalate (PET), a petroleum-based plastic, and polylactic acid (PLA), a biobased plastic, have a similar visual appearance thus they usually end up in municipal waste treatment facilities. The objective of this project was to develop an effective PET and PLA waste treatment process that involves pretreatment with deep eutectic solvent (DES) followed by biodegradation with a plastic-degrading bacterial consortium in a composting system. The DES used was a mixture of choline chloride and glycerol, while the bacterial strains (Chitinophaga jiangningensis EA02, Nocardioides zeae EA12, Stenotrophomonas pavanii EA33, Gordonia desulfuricans EA63, Achromobacter xylosoxidans A9 and Mycolicibacterium parafortuitum J101) used to prepare the bacterial consortium were selected based on their ability to biodegrade PET, PLA, and plasticizer. The plastic samples (a PET bottle, PLA cup, and PLA film) were pretreated with DES through a dip-coating method. The DES-coated plastic samples exhibited higher surface wettability and biofilm formation, indicating that DES increases the hydrophilicity of the plastic and facilitates bacterial attachment to the plastic surface. The combined action of DES pretreatment and bioaugmentation with a plastic-degrading bacterial consortium led to improved degradation of PET and PLA samples in various environments, including aqueous media at ambient temperature, lab-scale traditional composting, and pilot-scale composting.

Bioaugmentation with a defined bacterial consortium: A key to degrade high molecular weight polylactic acid during traditional composting.

Polylactic acid (PLA) is commercialized as a compostable bio-thermoplastic. PLA degrades under industrial composting conditions where elevated temperatures are maintained for a long timeframe. However, these conditions cannot be achieved in a non-industrial compost pile. Therefore, this study aims to degrade high molecular weight PLA films by adding a PLA-degrading bacterial consortium (EAc) comprised of Nocardioides zeae EA12, Stenotrophomonas pavanii EA33, Gordonia desulfuricans EA63, and Chitinophaga jiangningensis EA02 during traditional composting. With EAc-bioaugmentation, PLA films (5-30% w/w) had complete disintegration (35 d), 77-82% molecular weight reduction (16 d), and higher CO2 liberation and mineralization than non-bioaugmented composting. Bacterial community analyses showed that EAc-bioaugmentation increased the relative abundance of Schlegelella, a known polymer degrader, and interacted positively with beneficial indigenous microbes like Bacillus, Schlegelella and Thermopolyspora. The bioaugmentation also decreased compost phytotoxicity. Hence, consortium EAc shows potential in PLA-waste treatment applications, such as backyard and small-scale composting.