Our rivers and oceans are being clogged with plastic debris, which is doing
long-term environmental havoc that is just now beginning to be seen. But a
novel strategy that fuses chemical and biological processes might
significantly streamline the recycling procedure.
While a lot of the plastic we use has symbols suggesting it can be recycled
and authorities make a great deal about it, the truth is that it's more
difficult to accomplish than it is to say. Our waste streams are made up of
a complicated combination that may be challenging and expensive to separate,
and the majority of recycling systems only function on a single type of
plastic.
We are still far from the circular economy's aim in terms of plastics since
most present chemical recycling procedures result in final products of
noticeably lower quality that cannot be recycled themselves.
However, a novel strategy that first uses a chemical process to break down
mixed plastic waste into simpler chemical compounds, then uses genetically
modified bacteria to transform those compounds into a single, useful end
product, could pave the way for a promising new strategy to address our
plastic crisis.
This novel hybrid method, described in a recent
Science study, builds on earlier work that shown that a combination of several polymers
may be oxidized with the aid of a catalyst to break down and transform into
a variety of valuable compounds.
The technique is problematic since the resultant mixture of compounds
necessitates intricate separation procedures to extract and purify them. In
contrast to the byproducts of the majority of chemical recycling procedures,
the "oxygenates" created by this technique have an appealing quality: they
are significantly more soluble in water.
This makes it much simpler for living creatures to absorb them, providing
the opportunity to further refine them through biological processes. In
order to take advantage of this, the researchers genetically modified a type
of soil bacterium so that it would absorb the mixture of chemicals and
utilize them to create a single end product, a technique known as
"biological funneling."
The team's efforts resulted in the creation of two distinct strains, one of
which could manufacture b-ketoadipate, a precursor for a number of
performance-enhanced polymers, and another of which could produce
polyhydroxyalkanoates, a family of bioplastics employed in several medical
applications.
When the researchers put their hybrid strategy to the test, they discovered
that after 5.5 hours, a combination of polystyrene, polyethylene, and PET
could be converted into benzoic acid and terephthalic acid with an
efficiency of 60% and dicarboxylic acids with an efficiency of 20%.
The metal catalyst was then extracted from the mixture and given to their
unique bacteria. While the remaining chemicals were transformed into the
intended end product, some of them were absorbed by the bacteria to aid in
their growth. Overall, they had a 57 percent efficiency in turning the
plastic mixture into b-ketoadipate.
Although the researchers' method is still only a prototype, there are
already some potential options for expanding its use. Although they only
tested the process on three polymers, polypropylene and polyvinyl chloride
may both be added.
Existing continuous reactor systems might aid with oxygen delivery and
continually remove the byproducts to prevent degradation before the process
is complete. In addition, it ought to be feasible to modify other bacteria
strains to make a variety of other products.
This type of hybrid recycling technique has a lot of promise for handling
the complex variety of plastics we discard each day, however a thorough
investigation of the approach's economics is still required. Perhaps we're
not so far away from a genuinely circular plastic economy after all.
