Assessment of Integrated Microalgal-Bacterial Ecosystems for Bioenergy Production - Optimization-based Methodology

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Many microbial ecosystems, as part of their normal activity, have the potential to provide services to society and improve environmental quality. Some can degrade organic or trace contaminants that pollute water, air or soil. Others can transform waste materials into valuable renewable resources, including bioenergy, biomaterials and high-value products. This generic capability opens the possibility for combining several microbial ecosystems in integrated bioprocesses, where various types of bioenergy or biomaterials are produced and multiple sources of pollution are treated, all at the same time.The focus in this project is on integrated bioprocesses that couple a microalgae photobioreactor with an anaerobic digester. While microalgae are currently considered one of the most promising feedstocks for biofuels due to their high productivity of carbon-rich lipids, the said combination with anaerobic digestion provides an efficient means of recycling the nutrients present in the waste algal biomass--after lipid extraction. On the whole, integrated microalgal-bacterial ecosystems will be capable of producing bioenergy in the form of biofuel and biogas, while treating both flue gas and wastewater. However, unlike in traditional biorefineries where a spectrum of bio-based products and energy are obtained by processing an available biomass feedstock, growing the feedstock becomes an integral part of the process in an integrated microalgal/bacterial system. Therefore, a photobioreactor can no longer be designed and operated separately from the algal downstream processing. Special attention must also be paid to the microbial adaptation to environmental and operational changes as well as the strong interactions between the various kinds of microorganisms. This intricacy makes it extremely challenging to design and operate these processes solely based on engineering intuition.It is a principal aim of this project to investigate integrated microalgal-bacterial processes by applying systematic methods of process analysis, design and operation, that are based on mathematical models. Our objective is twofold: (i) make an assessment of integrated microalgal-bacterial systems for sustainable bioenergy production and CO2 capture; and (ii) determine reliable design and operation strategies. An important challenge is the presence of process variability and modeling uncertainty, which challenges the current state-of-the-art of optimization under uncertainty. It is therefore another principal aim of this proposal to develop the crucial methods and tools needed for the analysis and optimization of integrated microalgal-bacterial systems.While many experimental research and demonstration programs are being carried out in the UK and worldwide to identify the most suitable algae strains and expand algal biofuel production to a major industrial process, this project will be the first of its kind to apply a systematic, model-based optimization methodology, that takes full account of operational issues as well as their interplay with design decisions. It is expected that operational considerations will bring a first element of response regarding critical design decisions, such as the need to operate algae growth and lipid production in separate bioreactors, and whether or not to extract the lipids before the anaerobic digestion step. The ability to identify operational bottlenecks will also provide valuable insight and guidance for strain improvement, e.g. via genetic engineering. Finally, it has been argued that economically sustainable production of microalgae for biofuels may only be achieved if combined with production of bulk chemicals, food, and feed ingredients. While the coproduction of multiple compounds from microalgae remains a challenge, the methodology developed through this project will bring on key insight on the best way to achieve such biorefining.