Sludge hydrolysis for polyhydroxyalkanoate (PHA) production. Abstract, Lahti Science Day, Lahti, Finland, November 18, 2021. Oral presentation.

Climate change due to carbon emissions of fossil fuels into the atmosphere, and the accumulation of non-degradable waste plastic in the environment are among the major global threats. Global plastics production was 322 million tons, and the sector employed 1.5 million people in the European Union in 2015, while the market share of bio-based plastics was very small. The environmental problems associated with plastics and climate change are a burden on nature, biodiversity loss, and a threat to human health. To alleviate these problems, the microbiological accumulation of waste carbon into polyhydroxyalkanoates (PHAs) is being developed. PHAs can be used as raw materials for biodegradable plastics. The PHA production requires three bioreactors, one for biomass digestion into short-chain fatty acids (VFAs), one for cultivation of PHA-accumulating microbes, and a third to converting VFAs to PHAs. Different types of wastewater sludges were used as carbon sources, sludge for biogas production, sludge after biogas production, and sludge with nitrogen removal. The addition of sawdust to these sludge bioreactors was evaluated to see if it could improve the VFA yield. The results were statistically analysed and the final conclusion was that the sludge for biogas production allowed the best VFA production, while less VFAs were obtained from other sludges.