Development of Enzyme-Based Approaches for Recycling PET on an Industrial Scale

Abstract

Pollution by plastics such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyurethane (PUR), polyamide (PA), polystyrene (PS), and poly(ethylene terephthalate) (PET) is now gaining worldwide attention as a critical environmental issue, closely linked to climate change. Among them, PET is particularly prone to hydrolysis, breaking down into its constituents, ethylene glycol (EG) and terephthalate (TPA). Biorecycling or bioupcycling stands out as one of the most promising methods for addressing PET pollution. For dealing with pollution by the macrosize PET, a French company Carbios has developed a pilot-scale plant for biorecycling waste PET beverage bottles into new bottles using derivatives of thermophilic leaf compost cutinase (LCC). However, this system still provides significant challenges in its practical implementation. For the micro-or nanosize PET pollution that poses significant human health risks, including cancer, no industrial-scale approach has been established so far, despite the need to develop such technologies. In this Perspective, we explore the enhancement of the low activity and thermostability of the enzyme PETase to match that of LCC, along with the potential application of microbes and enzymes for the treatment of waste PET as microplastics. Additionally, we discuss the shortcomings of the current biorecycling protocols from a life cycle assessment perspective, covering aspects such as the diversity of PET-hydrolyzing enzymes in nature, the catalytic mechanism for crystallized PET, and more. We also provide an overview of the Ideonella sakaiensis system, highlighting its ability to operate and grow at moderate temperatures, in contrast to hightemperature processes.

Recycling and Degradation of Polyamides

“…Similar to PA, PET also has a certain degree of crystallinity, and both are typical condensation polymers. There are currently reports that enzymes can be used to depolymerize PET materials, and the progress of industrial composting research on PET is rapid [46][47][48][49][50][51]. Unfortunately, no enzyme has been found that can effectively degrade high-PA polymers [52][53][54][55].…”

Measuring PETase enzyme kinetics by single-molecule microscopy

“…The PETase enzyme derived from this microbe, Is PETase, was shown to convert PET to mono(2-hydroxyethyl) terephthalic acid (MHET), with trace amounts of terephthalic acid (TPA) and bis(2-hydroxyethyl)-TPA (BHET) as secondary products (3). This discovery set off a global interdisciplinary effort to identify, characterize and optimize PET degrading enzymes, with the hope that these biodegradation approaches can be scaled up to reduce microplastics pollution in the environment (4, 5).…”

Modulation ofIdeonella sakaiensisPETase active site flexibility and activity on morphologically distinct substrates by surface charge engineering

“…Over the last 20 years scientists have described several microbial enzymes that can hydrolyse polyethylene terephthalate (PET), one of the most abundant plastics materials on earth widely used in disposable food and drink containers 1-3 . Particular interest lies in exploiting these enzymes to enable re/up-cycling of discarded and accumulating PET waste, a significant global issue 4 .…”