Harnessing the power of bacteria to fight recalcitrant postconsumer PET-waste burden

Introduction: Polyethylene terephthalate (PET), one of the most widely used petrochemical-based thermoplastics, has significant harmful environmental and health impacts due to its improper disposal given its recalcitrancy to degradation under environmental conditions. Despite the available recycling technologies, many wasted PET products comprise impurities of different nature (e.g., oils, pigments, etc.), additives or other polymers, that impair their recycling. Therefore, novel approaches are still required to complement the existing ones. Objectives: This work aimed at the valorisation of post-consumer PET waste into valueadded bacterial biomass. Method: Post-consumer PET waste, comprising 95% PET, 5% polyethylene and traces of carbon black additives, was depolymerized via reactive extrusion, resulting in a material named REX-PET. This material was processed into an aqueous solution containing sodium terephthalate (TPA) that was used as the sole carbon source for the cultivation of Glutamicibacter nicotianae strain 24A, isolated from soil contaminated with plastic waste collected at a municipal solid waste management facility. Findings: The 62-h fed-batch bioreactor (3 L) cultivation of G. nicotianae strain 24A, under a controlled temperature of 30 ºC and a pH value of 7.0, yielded 9.4 g/L of dry biomass, with a protein content of 48wt%. A TPA consumption rate of 20 g/(L.day) was displayed by the culture that reached a TPA removal efficiency of 89% and a biomass yield of 0.4 g/g. Additionally, the biomass presented a bright yellow coloration indicative of the presence of a pigment that was extracted and characterized. Conclusion: This study demonstrated the potential of the newly isolated G. nicotianae strain 24A for the upcycling of post-consumer PET waste into bacterial biomass and pigments of high value, thus contributing for tackling the problems associated with the management of wastes containing this recalcitrant petrochemical-derived plastic contaminated with other chemicals, whose current recycling through other technologies in impracticable.