The effect of pH on polyhydroxyalkanoate accumulation in activated sludge under cellulose, hemicellulose, and lignin feed : hydrolysis stage

This thesis is part of a larger project where the main objective is to promote the bio-based circular economy through the development of low-carbon solutions and new sustainable businesses. The project carries out pilot projects and develops circular economy business opportunities for sludge and bioplastic solutions. The new solutions are related to the production of polyhydroxyalkanoates (PHA) from activated sludge carbon and the development and use of plastics together with companies. This thesis focused more specifically on evaluating how pH affects the hydrolysis of activated sludge carbon and accumulation of polyhydroxyalkanoates under the feed of cellulose, hemicellulose, and lignin to adjust the carbon to nitrogen ratio. This was done by calculating the organic matter and ash content of the activated sludge samples from the Lahti Aqua wastewater treatment plant and starting up different bioreactors with samples of the same sludge, together with the nutrients needed to keep microbes alive by making them to hydrolyze complex carbon sources and accumulate PHAs. Every day, over a period of approximately 15 days, two pH adjustments were made to the bioreactors, with samples taken from each bioreactor at the end of each adjustment. The samples were analyzed for the PHA that had accumulated in them, obtaining re-sults using gas chromatography and mass spectrometry (GC-MS) equipment. Finally, the results obtained were evaluated and it was assessed whether the established objectives were met, drawing some conclusions such as the concentration of PHA is higher at a pH 7 than at a basic pH between 9 and 10