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Earth Science

Mutant Enzyme Could Vastly Improve Recycling of Plastic Bottles (sciencemag.org) 35

Posted by EditorDavid from the good-for-the-bottle dept.
sciencehabit writes: Recycling isn't as guilt-free as it seems. Only about 30% of the plastic that goes into soda bottles gets turned into new plastic, and it often ends up as a lower strength version. Now, researchers report they've engineered an enzyme that can convert 90% of that same plastic back to its pristine starting materials. Work is underway to scale up the technology and open a demonstration plant next year.

The researchers generated hundreds of mutant enzymes changing amino acids as they went. They then mass produced the mutants in bacteria and screened them to find efficient breakers of plastic bonds. After repeating this process for several rounds, they isolated a mutant enzyme that's 10,000 times more efficient at breaking down an important bond that allows plastic to be recycled.

The team is currently building a demonstration plant that is expected to recycle hundreds of tons of plastic per year. The enzyme can't recycle other major types of plastics, such as polyethylene and polystyrene, which have bonds between building blocks that are harder to break. But if successful, it could make it help society deal with one of the most challenging plastic problems we face.
John McGeehan, who directs the center for enzyme innovation at the University of Portsmouth, also tells Science that now recycling companies typically melt plastics together to make carpets or other low-grade plastic fibers that will eventually end up in a landfill or get incinerated.

"It's not really recycling at all."
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Mutant Enzyme Could Vastly Improve Recycling of Plastic Bottles More

Mutant Enzyme Could Vastly Improve Recycling of Plastic Bottles

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  • Then it will eat all our fancy new plastic plumbing.

  • Polyethylene Terephthalate (Score:5, Informative)

    by careysub ( 976506 ) on Sunday April 12, 2020 @10:48AM (#59936622)

    To help the average slashdotter here (who just reads the summary), the plastic this enzyme digest is the popular bottle plastic PET or polyethylene terephthalate, also used (in vastly smaller amounts) in 3D printing. It converts the PET back into its starting materials - terephthalate and ethylene glycol - which can be obtained from the reaction mixture in pure form.

    And no, we won't have microbes eating plastic. They just make the enzyme which is used in a reactor at a temperature well above the survival temperature of any engineered production microbe (72 C).

    • Best summary ever. Thank you!

    • Re: (Score:2)

      by Eirele ( 6731032 )

      Just adding some extra info to your previous comment, because Slashdot summary states that the enzyme doesn't work on polyethylene alone:

      The enzyme can't recycle other major types of plastics, such as polyethylene and polystyrene, which have bonds between building blocks that are harder to break.

      and apparently Google doesn't help people easily understand the difference between Polyethylene (PE) and Poly(Ethylene Terephthalate). So, I found in some very old book of mine some good info:

      Polyethylene (PE)

      Po [wikipedia.org]

    • Up front, I don't know anything about the subject. From what I understand though, the barriers to increased recycling are more often how to clean it. The strength of the recycled plastic is not the main reason why plastic is not recycled more. Although I can see this being helpful in some cases, I don't see this as even a potential game changer. If this is true, someone please correct me if I am wrong, the title should be something more like "mutant enzyme could vastly improve the quality of recycled pl

      • Re: (Score:1)

        by Eirele ( 6731032 )

        I think some way to try to explain this matter is: Every kind of enzyme are used to be very specific in what they can "cut", e. g..: some specific chemical bond. So this enzyme will be able to degrade some kind of plastics because they have this specific region for docking (and subsequent cleavage), but with other kind of polymers this enzyme will be able to do nothing.

    • Hope this works better than recycling paper. Around here, pizza boxes go to landfill because they're contaminated by the cooking oil. That somehow makes the recycling process unworkable.
    • I'm torn as to which poster in this particular thread to respond to in order to ask a follow up question.

      First.. thank you (all the people providing useful information here) for breaking the normal Slashdot mold and being so informative.

      I'm not able to read the paper as I believe it's several degrees above my level of chemistry and materials.

      When I read these "too good to be true" articles, my initial knee jerk reaction is to wonder "what's the catch?". And the first thing that comes to mind is that while i

      • Re: (Score:1)

        by Eirele ( 6731032 )

        I'm torn as to which poster in this particular thread to respond to in order to ask a follow up question.

        First.. thank you (all the people providing useful information here) for breaking the normal Slashdot mold and being so informative.

        You are welcome.

        I'm not able to read the paper as I believe it's several degrees above my level of chemistry and materials.

        When I read these "too good to be true" articles, my initial knee jerk reaction is to wonder "what's the catch?". And the first thing that comes to min

  • When they say, " pristine starting materials" do they mean crude oil?

    • Re:fuel? (Score:5, Informative)

      by careysub ( 976506 ) on Sunday April 12, 2020 @11:12AM (#59936712)

      They mean terephthalate (terephthalic acid) and ethylene glycol, the actual chemicals from which the PET is made. The former needs an aromatic nucleus as a starting point, p-xylene usually, which would be obtained from petroleum (plant based production is possible though). Ethylene glycol though only needs carbon monoxide and hydrogen, and so various raw materials can be used with existing industrial methods.

    • ...or dinosaurs?

    • Re: (Score:1)

      by Eirele ( 6731032 )
      I suppose they are probably referring to some polymer nano-particles used in a polymerization process. But in this case in the reverse order because the polymer is being decomposed by the enzyme, generating a lot of nano-fragments.
  • Silver bullets,
    silver bullets,
    silver bullets, one and all.
    If only
    silver bullets
    would do anything at all.

  • Great, this will get out... (Score:4, Funny)

    by sinij ( 911942 ) on Sunday April 12, 2020 @11:24AM (#59936760)
    We will have to deal with plastic "rust" once this gets out into the wild.

    • There already is plastic 'rust' .

      The automotive and white goods industry learned long ago to make critical parts out of 'greener' plastics that wear out and force people to buy parts or replace the whole car or appliance more often.

      Most big companies have 'continuation engineeing' teams on staff to drive costs down and design products to wear out soon after the warranty period ends.

  • "It's not really recycling at all."

    Yes, it is recycling. It's not endless recycling but there are very few things which are.

  • Plastics are biodegradable. It seems to be taking a long time for people to recognize this. First, it was ocean archaea. Now, lab-grown bacteria.

    • Re: (Score:2)

      by epine ( 68316 )

      Plastics are biodegradable.

      Nothing is so clueless as citing red dwarf [wikipedia.org]—and not even knowing it. Only not even red dwarf recycles plastic all the way back to hydrogen. For that particular fly in the ointment, I think the blame falls on Slartibartfast.

  • Or we could stop drinking water in bottles like a bunch of corporately mind-fucked idiots while businesses are required to install not one but two water fountains (one for the disabled) around their buildings.
    • Pretty sure water fountains are about to disappear from the public altogether. Though I'd imagine that we will likely see accessible water taps for filling bottles pretty much everywhere.

      It's truly horrifying to shine a black light over the common public water fountain.

      • Yeah, that. If you're going to mandate drinking fountains you also have to mandate regular sanitization of them. They are frequently disgusting.

  • https://interestingengineering... [interestin...eering.com]

    Anyone want to debunk this?

  • why does the original movie version of The Andromeda Strain come to mind?

  • Recycling can help, but the problem isn't lack of recyclability. Plastics are made from oil, and we get oil from underground. So simply burying plastic in landfills creates a zero net impact on the environment. But the problem is people who litter - they don't throw plastics away in the trash when they're done using them. They throw it away on the ground, in rivers, and in the ocean. Recycling doesn't help with that, as someone who is unwilling to throw away plastic in a trash can, will be just as unwill

    • Re: (Score:1)

      by Eirele ( 6731032 )

      Recycling can help, but the problem isn't lack of recyclability. Plastics are made from oil, and we get oil from underground. So simply burying plastic in landfills creates a zero net impact on the environment.

      The process of burying plastics can only lead to create an impermeable layer underground, that will block the rain water from being filtered and safely return to the groundwater in its natural renewable cycle. This can cause a lot of environmental problems.

      On the contrary, if you have to create a s

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