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.