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MIXed plastics biodegradation and UPcycling using microbial communities

Periodic Reporting for period 2 - MIX-UP (MIXed plastics biodegradation and UPcycling using microbial communities)

Reporting period: 2021-01-01 to 2021-12-31

±359 million tonnes (Mt) of plastics are produced world-wide in 2018, increased by 15% in the last 5 years, and a staggering 800 Mt are forecasted to be produced by 2050. In 2016 the US with 42 Mt were highest in plastic waste generation, succeeded by the EU (29.8 Mt), followed by countries with the highest populations, India (26.3 Mt) & China (21,6 Mt). Only a small fraction (12%) of that plastic is recycled and of that only 10% has been reused more than ones. The 7 main plastic polymers account for 92% of all primary produced plastic ever made (1950-2015: 8,300 Mt). The largest groups are PET (36%), PP (21%), and PVC (12%), followed by PET, PUR, PS (10% each).

The EC aims at transforming the EU into a resource efficient economy with a central place for plastic waste. This involves a far-reaching change in its Plastics Strategy, moving away from the current linear value chains towards a circular bioeconomy. Effective plastic recycling poses a major challenge for sustainability, as plastic currently degrades each time it is recycled. Technological solutions as part of a circular economy can form only part of more radical changes required in human behavior’s like throw-away mentality symbolized by single-use consumer plastics or unnecessary packaging. MIX-UP makes a strong commitment to help the EC realise this vision in a project researching novel routes to valorise mixed plastic waste streams. The MIX-UP partners envision a better plastic future built on the ‘6 R’ principles (rethink, refuse, reduce, reuse, recycle, replace). MIX-UP is also addressing the industry and the public interest to establish a sustainable plastic economy. The global dimension of this problem is reflected in an intercontinental effort of two consortia originating from the 2 main plastic producers: the EU and China. The MIX-UP consortium includes 7 universities and 3 research centres, complemented by 2 partners from industry and SMEs, resp. New solutions for the upcycling of mixtures of recalcitrant and biodegradable plastics are desperately needed. MIX-UP addresses this need by unlocking these plastics as carbon source for the biotechnological conversion to value-added products, incl. biodegradable plastics and chemicals tailored for a circular bioeconomy with built-in end-of-life considerations.

The ground-breaking objective of MIX-UP is the establishment of mixed plastics waste as abundant 2nd generation feedstock for industrial biotechnology – plastics waste as a valuable resource for the future. This goal will be achieved by the bioconversion of unsorted, mixed plastics waste into value-added, sustainable biomaterials using heavily engineered enzyme mixtures for depolymerisation & mixed microbial cultures for upcycling of released plastic monomers to valuable products.
The main idea of MIX-UP is to showcase a novel approach to the circularity of the plastic life cycle. The overall concept is depicted in the Figure.

Enzyme production and mixed enzymatic hydrolysis of mixed plastics
Although plastics are generally considered to be very recalcitrant in nature, there are microbes and enzymes that can degrade them. We have identified PET, PLA and PUR degrading enzymes and characterized their activity. We started engineering the enzymes themselves towards a greater activity, stability (thermo-) and efficiency, and we have also optimized the process in which these enzymes are applied to degrade plastic waste and the optimized processes to produce these enzymes in large volumina. Additionally, these enzymes will be expressed in defined microbial mixed cultures or as envisioned in a consolidated bioprocess with simultaneously implemented microbial upcycling.

Microbial plastics monomer metabolism
The released metabolites, plastic mono- and oligomers from PET, PUR, PLA, PHA and PE will be fed to dedicated microbial communities (e.g. Pseudomonas putida, Halomonas bluephagensis) and convert the substrate into central metabolites, which provide afterward the building blocks for the synthesis (Valorisation) of novel polymers (e.g. PHAs), products (e.g. HAAs, biosurfactants) or building blocks for chemo-catalysis.

Downstream processing and product recovery
We started optimizing downstream processing and the recovery of products (PHAs, HAAs) by conditional release of the intracellular products and separation. The recalcitrant residues (as model compounds) separated will be subjected to chemical transformation, also cracking the persistent ester bonds.
The entire bioprocess will be further optimized performing metabolic engineering in an integrated manner by considering the upstream (strain and microbiome development, protein engineering), midstream (fermentation), and downstream (recovery and purification) processes altogether.
Novel microbes and enzymes with activity on so far as recalcitrant regarded polymers have been identified. Novel separation techniques have been developed and many different microbes have been engineered for metabolization of plastic monomers. Furthermore, we expanded the toolboxes for synthetic and computational biology.
The ultimate goal of the circular plastics economy are products, which are 100% recyclable and used as long as possible. Nevertheless, chemical recycling is costly and produces lower quality materials, in terms of thermal and mechanical properties.
MIX-UP is a technological response to these challenges and could be a possible mediator for the upcycling of almost completely fossil resources-based mixed plastics waste to biodegradable and sustainable polymers.

MIX-UP will develop valorisation strategies for multi-million-tonne plastic waste streams thereby reducing environmental impact while at the same time accelerate the development of promising biotechnology products. For future use a second-generation feedstock of approx. 4,900 Mt of plastics waste has been stored in the environment, mainly in landfills. These incredible resources are waiting for a second chance. As an added benefit, the bio-depolymerisation of PET, PUR, PE, and PS will yield building blocks such as TA, AA, EG, BDO, MDI, and TDI, which in themselves have a market size of well over 10 million euro per year each. Furthermore, the development of product formation modules in consortia for HAA, vicinal diols, biosurfactants, antimicrobial polymers, and fatty alcohols will provide proof of concept for the bio-production of these highly promising but hitherto underdeveloped bio-chemicals for diverse large-scale applications ranging from plastics monomers to detergents. Biodegradable polymers can be recycled, but when leaked to the environment they break down into their constituents CO2, CH4, and water, catalysed by microorganisms under aerobic or anaerobic conditions.

If successful, MIX-UP will enable several highly visible social impacts:

[i] By providing economic incentives of waste valorisation, recycling initiatives will be increased.
[ii] Increased recycling will reduce waste, immediately visible in people’s garbage and saving money on municipal waste taxes.
[iii] The development of efficient PHA/PUR production methods and new PHA and PUR-based materials will lead to the market emergence of novel biodegradable polymers in medical, technical and even packaging applications.

These aspects will be the major driving forces used by MIX-UP dissemination channels to promote the social acceptance of the innovative technology that enables this positive change.
Schematic overall concept of the MIX-UP project