Production of polymers from a papermills wastewater using HTC substrate. : Investigating the viability of using wastewater sludge from Skoghalls’ papermill in combination with filtrate from HTC of sewage sludge to produce biological plastic producing poly

Abstract: Since their conception, plastics have been a dominant product due to the versatility of use, and readily available raw materials. However, the production and consumption of synthetic plastics have continued to increase over the years, leading to a significant rise in plastic waste and its associated environmental impacts, such as the detrimental effects plastic waste has on ecosystems, including the presence of toxic microplastics and risks to marine life, are becoming the focus of criticism. Moreover, the contribution of plastic production to global warming through the usage of petroleum as a raw material cannot be understated. Solutions are being sought after to reduce the impact of this plastic waste, with one such solution being the replacement of the raw materials involved in plastic production. If a biologically degradable plastic product can be produced, then even if the dangers associated with plastic waste cannot be removed, they can be reduced. One method is the production of plastics using polyhydroxyalkanoates (PHA) as a replacement as these are shown to have similar properties as synthetic plastics while being 100% degradable. PHA production has existed since the 1960’s, but the process has always been too expensive to be a viable alternative to the cheaper petroleum-based products. A reduction of the production costs is needed for PHA to be an economically viable alternative, and there are two areas that contain the highest costs; The usage of expensive monocultural bacteria, and specially crafted carbon sources used to feed these bacteria to stimulate PHA accumulation. By switching to a multi-cultural bacterium and using readily available organic carbon sources can the costs of production be brought down, allowing the prospective biological plastics a chance to compete in the plastic market.  This thesis focuses on the usage of a multi-cultural bacterium collected from the water purification plant of a papermill, and the filtrate from the hydrothermal carbonisation (HTC) of sludge as the organic carbon source as materials in the production of PHA. The aim of the thesis is to investigate how successful PHA accumulation can occur using these two readily available waste products, and if successful to analyse the characteristics of any biological plastic that could be produced. The trials were performed in a cylindrical tank; one benchmark trial using acetic acid as the carbon source to be used as a reference for successful PHA accumulation, and five trials investigating the PHA accumulation that occurred using the HTC filtrate as the carbon source. The trials were analysed by extraction, TGA, FT-IR, TOC, and SS. During the trials pH, temperature and concentration of diffused oxygen was monitored. The trials indicated that the accumulation of PHA was possible, with various results. The most successful accumulation was observed in trial I-1, where PHA reached 12.45%, only slightly lower than the benchmark trials accumulation of 13.6%. Trials I-2 and I-3 also showed potential for high PHA content according to FTIR analysis. However, trials F-1 and F-2 failed to accumulate any PHA, and the inhibiting factors behind this were not fully understood. Possible reasons included high ammonia levels, incompatible bacteria, or imbalanced nutrient ratios. Various extraction methods were attempted to isolate the polymers found within the biomass for use in plastic production. While one extraction method was successful and used to analyse the PHA content found in the biomass, the amount of polymer that was extracted via this method was too small for use in plastic production, and as such the characteristic investigation of the plastic was unable to be completed. Overall, the study identified successful PHA accumulation in some trials but faced challenges and uncertainties regarding inhibiting factors and extraction methods. Future improvements should focus on standardizing experimental conditions and optimizing extraction techniques for better results.