Biodegradability steps

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1) Biofilm Formation

In this phase the microorganisms attach to the surface of the polymer and adapt their metabolism for polymer degradation and utilization. Microorganisms form a beneficial community attached and protected by cover from polysaccharides and proteins forming a resistant biofilm.

There are two different types of microorganisms in biodegradation:

  • Microorganisms that can attach to the polymer and directly degrade it.
  • Microorganisms, that cannot degrade the polymer itself, but they benefit from the activity of the first group.2


The surface properties (size, roughness), crystallinity, chemical structure etc. define how easily microorganisms attach to the polymer surface.

2) Depolymerization

Extracellular depolymerases produced by the microorganisms cleave the bonds of the polymer molecules. Shorter chains – oligomers, and monomers are the result.

3) Bioasimilation

Small molecules can be absorbed by the microorganisms and used for building of the microbial cell or energy conversion. This conversion is called mineralization.1

The result of the biodegradation is microbial biomass, CO2 in case of aerobic degradation or CH4 in anaerobic conditions.

Biodegradable polymer is the one, which is fully mineralized. However, many methods for biodegradability measurements do not cover all the steps of biodegradability.

Learn more about How is biodegradability measured.

References

1 Dilkes-Hoffman, L. S., P. A. Lant, B. Laycock and S. Pratt. The rate of biodegradation of PHA bioplastics in the marine environment: A meta-study. Marine Pollution Bulletin. 2019, 142: 15-24. doi: https://doi.org/10.1016/j.marpolbul.2019.03.020.

2 Meereboer, K. W., M. Misra and A. K. Mohanty. Review of recent advances in the biodegradability of polyhydroxyalkanoate (PHA) bioplastics and their composites. Green Chemistry. 2020, 22(17): 5519-5558. doi