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Polyester (PET) hydrolases (23/05/22 16:34:21)
    In a recent press release from a German university (Leipzig) we are informed of a specially active polyester hydrolase found in a bacterium from a city dump. That's good news: single-use food containers and old clothes can now be split into the monomers: terephtalic acid (p-benzenedicarboxylic acid) and ethylene glycol and reused - if the finding results in effective and cost-effective protocols. I see then a succession of processes: First dissolving and washing out the PET from an unsorted mix, then a second specific method, perhaps enzymatic oxidation via a P450-enzyme of polyethene and polypropylene yielding a much more diverse mix of small molecules.

    "Low-density polyethylene is the most abundant plastic waste discarded in landfills in the form of plastic bags (69.13%). LDPE is mostly amorphous, with short branches (10–30 CH3 per 1,000 carbon atoms) and composed of one or more comonomers, such as 1-butene, 1-hexene, and 1-octene. This branching system makes LDPE chains more accessible and the tertiary carbon atoms at the branch sites more susceptible to attack. The physical arrangement of the polymer chains in LDPE and a lower content of vinylidene defects, which have been shown to be directly correlated with oxidization of the polymer makes it more biodegradable than High-density polyethylene (HDPE). Further, the molar mass of HPDE is much higher, possibly making it more difficult for microorganisms and their oxidizing enzymes to access the polymer chains (Sudhakar et al., 2008; Fontanella et al., 2010). Few comparison studies have been made on the biodegradability of various pre-treated polyethylene materials, including, LDPE, HDPE, and linear low-density polyethylene (LLDPE) films of different thickness by Rhodococcus rhodochrous, which is one of the most efficient bacteria for PE biodegradation (Fontanella et al., 2010). Structural variations in PE polymers formed during polymerization and subsequent processing, such as unsaturated carbon–carbon double bonds, carbonyl groups, and hydroperoxide groups (Ojeda et al., 2011) have been shown to be consumed first by the bacteria resulting in rapid growth.

    Many of the species known to degrade PE are capable of hydrolyzing and metabolize linear n-alkanes, like paraffin molecules (e.g., C44H90, Mw 618) (Haines and Alexander, 1974). Alkane hydroxylases (AHs) are the key enzymes involved in aerobic degradation of alkanes by bacteria. The first step involves hydroxylation of C-C bonds to release primary or secondary alcohols, which are oxidized to ketones or aldehydes, and subsequently to hydrophilic carboxylic acids (Alvarez, 2003; Watanabe et al., 2003). Microbial oxidation reduces the number of carbonyl-groups due to the formation of carboxylic acids. "

    "Rather, both the insect digestive system and the larval gut microbiome are required to achieve accelerated biodegradation of the PE polymers.

    In recent years, biodegradation of other petro-plastics, like PE and PS, insect larvae such as Yellow Mealworms (Tenebrio molitor) (Billen et al., 2020), Dark Mealworms (Tenebrio obscurus) (Brandon et al., 2018; Peng et al., 2019), Superworms (Zophobas atratus) (Peng et al., 2020b), Lesser Waxworms (Achroia Grisella) (Kundungal et al., 2019), and by snails (Achatina fulita) (Song et al., 2020), have been reported."

    (https://www.frontiersin.org/articles/10.3389/fmicb.2020.580709/full)

    A lot of work needs to be done to obtain high enough capacity (rapid degradation). The patents, I guess, will have to be on the reactors. So there will be competition.
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Polyester (PET) hydrolases