Novel bioprocess design for bioplastic production using membrane bioreactors

Membranes in bioreactor systems are becoming increasingly prominent with the advancements in membrane technology, broadening their application beyond their conventional role as separation units. Over the past few decades, the wastewater industry has adopted the use of membrane bioreactors, employing membranes as effective aeration devices and for resource recovery. There is an increasing interest in using membranes in industrial biotechnology. This thesis explores membrane bioreactors as innovative systems for bioprocess applications with the objective of leading the development of a new platform technology for the bioeconomy. In the first part of the thesis, an overview of the current literature on membrane bioreactors for the production of value-added products was presented. This section outlined the ways in which membranes can be integrated with bioreactors and summarized the progress in this area. This section also created a framework for future studies, outlining the steps for developing bioconversion processes using membrane bioreactors. The second part of the thesis explores different membrane bioreactor configurations where membranes were used as gas transfer devices. In this section, the operational conditions of the novel membrane bioreactor were studied using a model microorganism that produces a polymer that could be used to produce bioplastic. The novel bioreactor is further characterized in terms of gas transfer efficiency, microbial growth and optimized bioplastic production. Different operation modes such as batch, fed batch and continuous modes were investigated and the effect of different feeding strategies on biomass growth and bioplastic production was studied. This study is the first study to investigate microbial bioplastic production in a membrane bioreactor where membranes are used for gas transfer. The third part of the thesis examines biofilm formation in a single tube membrane bioreactor system, using the same microorganism. The study focused on the gas transfer mechanisms and explored the effect of biofilm thickness on substrate transfer diffusion rates. It is the first study to date that investigates the biofilm characteristics of the model microorganism on a tubular membrane. The last part of the thesis focused on the simulation of industrial scale production of the bioplastic in interest, where the effect of using different carbon sources as feedstock on the selling price was investigated. The study compared using fructose, formic acid and CO2 as the main carbon source, where experimental bioplastic yields with the wild-type microbial strain was used for calculations. A sensitivity analysis was performed to study the influence of the cost of each carbon source and the most feasible scenario was determined. The study showed that while using formic acid and CO2 aids in addressing circular economy concerns through CO2 fixation, the resulting bioplastic is not yet economically competitive in the plastic market. Overall, this thesis investigates the applicability of membrane bioreactors to produce bioplastics, aiming to pioneer the research on gas-transfer membrane bioreactors for the potential application within the bioeconomy.