Enzymatic Remediation of Polyethylene Terephthalate (PET)–Based Polymers for Effective Management of Plastic Wastes: An Overview

Abstract

Globally, plastic-based pollution is now recognized as one of the serious threats to the environment. Among different plastics, polyethylene terephthalate (PET) occupies a pivotal place, its excess presence as a waste is a major environmental concern. Mechanical, thermal, and chemical-based treatments are generally used to manage PET pollution. However, these methods are usually expensive or generate secondary pollutants. Hence, there is a need for a cost-effective and environment-friendly method for efficient management of PET-based plastic wastes. Considering this, enzymatic treatment or recycling is one of the important methods to curb PET pollution. In this regard, PET hydrolases have been explored for the treatment of PET wastes. These enzymes act on PET and end its breakdown into monomeric units and subsequently results in loss of weight. However, various factors, specifically PET crystallinity, temperature, and pH, are known to affect this enzymatic process. For effective hydrolysis of PET, high temperature is required, which facilitates easy accessibility of substrate (PET) to enzymes. However, to function at this high temperature, there is a requirement of thermostable enzymes. The thermostability could be enhanced using glycosylation, immobilization, and enzyme engineering. Furthermore, the use of surfactants, additives such as Ca 2+ , Mg 2+ , and hydrophobins (cysteine-rich proteins), has also been reported to enhance the enzymatic PET hydrolysis through facilitating easy accessibility of PET polymers. The present review encompasses a brief overview of the use of enzymes toward the management of PET wastes. Various methods affecting the treatment process and different constraints arising thereof are also systematically highlighted in the review.

Progressing Plastics Circularity: A Review of Mechano-Biocatalytic Approaches for Waste Plastic (Re)valorization

“…A combination of ultrasonication and enzymatic catalyzed reaction systems has been recently reported ( Kawai et al, 2019 ). Under optimized conditions, sequential enzymatic-ultrasonic treatment was demonstrated to lead to the release of lower molecular weight products including a higher release of terephthalic acid in solution ( Maurya et al, 2020 ). A significant increase in hydrolysis rate was observed when enzyme-catalyzed hydrolysis was combined with ultrasonication in less crystalline polymers due to more available surfaces for cavitation phenomenon ( Pellis et al, 2016 ).…”

Engineering Microbes to Bio-Upcycle Polyethylene Terephthalate

“…Also, computational and machine learning approaches enable the researcher to discover novel potent PET enzymes from metagenomics databases (Danso et al, 2018;Furukawa et al, 2019;Subramanian et al, 2019). These enzymes belong to esterase, cutinase, and lipase families, and may evolve in a PET-rich environment (Roager and Sonnenschein, 2019;Alam et al, 2020;Maurya et al, 2020). The discovery of the bacterium Ideonella sakaiensis harboring hydrolyzing enzymes PETase and MHETase has revolutionized the field.…”

Prospects of Using Biocatalysis for the Synthesis and Modification of Polymers

“…In addition, bio-polyethylene and bio-polyethylene terephthalate also cannot be considered biodegradable, although they can be obtained from bioethanol produced by fermentation of glucose and bioethyleneglycol, respectively. However, recently there has been a growing interest in the development of technologies for poly(ethylene terephthalate) depolymerization aiming at monomer recycling, and in this context, enzyme-catalyzed hydrolysis has been recognized as a promising alternative [ 50 , 51 , 52 , 53 , 54 , 55 ]. Therefore, the non-biodegradability of poly(ethylene terephthalate) may be reassessed in the nearest future.…”