Transforming waste carbon to plastic raw material

Global climate warming and plastic accumulation in the environment can be mitigated by recycling waste carbon to biodegradable plastics.

Among the major global threats are climate change due to the carbon release from fossil fuels into the atmosphere, and the accumulation of non-degradable waste plastic in the environment. In 2015, global plastics production was 322 million tons, and the sector employed 1.5 million people in the European Union, while the bio-based plastics shared only a very small market portion. Climate change and plastics related environmental problems are a burden on nature and biodiversity, and a threat to human health. An approach under development, that alleviates these problems, is microbiological accumulation of waste carbon into polyhydroxyalkanoates (PHAs), a raw material for biodegradable plastics. To achieve this, three bioreactors are required, one to biomass digestion into short-chain fatty acids (VFAs), another to cultivate PHA-accumulating microbes, and a third to transform VFAs to PHAs. The development was began with the optimization pH conditions for biomass hydrolysis reactors, while now the goal is to move to the treatment of various waste fractions and the development of accumulation reactors. In particular, wastewater sludge carbon would be important to convert into a raw material for plastic, as sludge has few other uses due to its potential contaminants. Further challenge is the sludge after biogas production, where the decomposing of volatile organic solids (VS) has caused an increase in the portion of fixed solids (FS) and inhibition of microbiological processes. Different microbial communities are required for high VS and FS bioreactors.

Kouzi AI, Puranen M, Kontro MH. 2020. Evaluation of the factors limiting biogas production in full-scale processes and increasing the biogas production efficiency. Environmental Science and Pollution Research 27, 28155-28168.