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

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.

It is anticipated that the project will also has a large number of non-academic potential users and beneficiaries. Because the impetus for this research comes from both the exploitation of microbial ecosystems and the optimization technology, the potential impacts reflect this dichotomy.

- The most direct non-academic users of the project results will be companies developing and exploiting microbial ecosystems, such as microalgae culturing and anaerobic digestion processes. More generally, potential applications can be for the production of bioenergy (e.g., hydrogen, methane, ethanol or biodiesel), the treatment of gas and liquid wastes (industrial and/or municipal), or the output of high-value products (e.g., chemical or nutraceutical products). This research therefore has strong ties with the emerging paradigm of biorefineries, defined by the International Energy Agency (IEA) as "the sustainable processing of biomass into a spectrum of bio-based products and bioenergy." In particular, there has been much speculation about the fact that such biorefineries may play a major role in producing chemicals and materials that are traditionally produced from petroleum. Coming from a different angle, biodiesel from microalgae is currently considered one of the most promising alternatives since it has the potential to completely displace petroleum-derived transport fuels without adversely affecting the supply of food and other crop products. It is therefore not surprising that energy giants, such as BP, Shell and ExxonMobil, have recently started large research initiatives on algae-derived biofuel.

- Chemical and pharmaceutical companies will also be a major beneficiary of the optimization technology developments throughout this project. Many Chemical processes are hard to model accurately due to complex and intricate physicochemical phenomena and there is substantial uncertainty concerning resource availability, product prices and demands, plant/process unit availability and reliability, etc. Managing uncertainty efficiently is thus a major incentive in such industry for designing and operating safer and more environmentally benign plants, and at the same time improving product quality and decreasing production costs in an increasingly demand-driven and competitive market. The Industrial Research Consortium of the Centre of Process Systems Engineering (CPSE), which brings together major chemical companies that heavily rely on optimization methods, will serve as a means for dissemination of the developed technology and software. Ultimately, the scope of this research will not be limited merely to chemical industries. It is believed that other industrial sectors--such as energy production, transportation and logistics, aeronautics and aerospace--can also greatly benefit from this technology.