From Trash to Cash: Current Strategies for Bio-Upcycling of Recaptured Monomeric Building Blocks from Poly(ethylene Terephthalate) (PET) Waste

Plastic pollution has been a topic of grave concern worldwide due to major environmental, economic, health, and social impacts. Nevertheless, our society is far from casting plastics aside since they are essential for several applications (e.g. food packaging, automotive, electronics, building, and construction). Poly(terephtalate ethylene) (PET), an important synthetic polyester derived from petroleum, is extensively used in plastic packaging (mainly bottles and trays). Unfortunately, no greener polymer alternative has large-scale production to meet global demand. Consequently, plastic recycling is the most sustainable approach to manage the massive amounts of post-consumed PET materials, by recovering its monomeric units: terephthalic acid and ethylene glycol. However, current recycling methods are still costly, leading to more expensive reclaimed PET monomers than virgin ones obtained from fossil sources. Recently, PET upcycling emerged as a profitable strategy to value the reclaimed monomers by converting them into molecules with higher added value, enhancing the recycling process viability. In this review, we addressed all valuable commodities produced from the conversion of PET monomers catalyzed by microorganisms, as an eco-friendly process known as biological upcycling or bio-upcycling. We provided an outlook regarding potential markets and highlighted the benefits of the PET bio-upcycling route over the actual industrial production of each commodity. Moreover, we discussed different PET recycling methods employed to recover monomers prior to the bio-upcycling step, highlighting the pros and cons. Additionally, we addressed critical considerations about the major challenges regarding this novel recycling strategy, particularly in upscaling from lab-scale stage to real-world implementation.