Browsing by Author "Kerpo, Maija-Stiina"

Plastic industry has been a great success story, and plastics are used everywhere around us. They are of low cost, durable, and they have good mechanical and thermal properties. However, there is a growing concern over the use of these conventional plastics produced from hydrocarbons, disposal being the major problem. These petroleum derived plastics take several years to decompose, and they produce harmful toxic compounds during degradation. Therefore, an alternative is needed for future economical and ecologically safe polymers. Polyhydroxyalkanoates (PHAs) are one such alternative. They are bio-based, fully biodegradable and biocompatible polymers produced by various microorganisms. PHAs have comparable properties to conventional plastics like polypropylene and polyethylene, but they can be biosynthesized from renewable resources. However, the production of PHA has been limited especially due to its high production cost, caused by the use of pure cultures and sterilized media. Therefore, there is a great interest to use mixed cultures and waste streams like wastewater treatment sludge to produce PHAs. Economic evaluation has shown that the production costs of PHA can be reduced over half if renewable waste materials and activated sludge is used. In this study mixed microbial consortia (MMC) in wastewater sludge was used with feast and famine method to produce PHAs in laboratory scale. This study aimed to find the optimal process parameters and conditions for PHA production. The first three feast and famine fermentations with oxygen limitation showed no PHA accumulation, so the remaining two fermentations were performed in aerobic conditions. When keeping the fermentation aerobic, phosphorus will limit the bacterial growth eventually, since the phosphorus level in wastewater sludge is very low. As a result, a notably high PHA yield was gained with aerobic fermentation in room temperature and pH varying between 6.0 – 7.5. According to this study, PHA production from wastewater sludge requires aerobic conditions throughout the fermentation. However, there are still some points to consider for future experiments; dilute wastewater sludge could be concentrated before fermentation to get higher PHA yield per volume, as well as sludge feedings could be combined to only one feeding to accelerate the process. How to opt out the hydrolysis part from the beginning of the fermentation would also be worth studying in the future. Nevertheless, PHA production from activated wastewater sludge using MMC could be possible in a larger scale. This would be beneficial from the circular economy point of view, transforming waste into a valuable raw material, while reducing emissions, the use of feedstock, and energy in the process.