Using oscillatory flow and non-Newtonian media to enhance industrial processing of microalgae and other microswimmers

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The importance of microorganisms is well-documented, both in biological ecosystems and in engineering applications. Microalgae are a particular type of microorganism currently grown on an industrial scale in photo-bioreactors for the production of chemicals, effluent treatment, carbon capture and biofuel production. Microalgae biofuel production in particular has been gaining momentum relative to more traditional feedstocks (e.g. sugar cane) due to potential advantages in terms of sustainability. However game-changing engineering of algae-to-fuel technology, for example in the design of optimised cultivation bioreactors that are really competitive with established fuels, requires a much better rheological understanding and characterisation of algae suspensions. Because in so-called 'active' suspensions swimming microalgae are able to self-propel using flagella, their interaction with flow fields is far more complex than that of non-motile particles, presenting both an opportunity and a challenge. Exploiting swimming activity could lead, for example, to novel separation and 'steering' methods. Nevertheless despite the recognised potential of novel individual and collective behaviour of swimmers for process engineering, experimental studies on algae suspension rheology remain limited and still present basic puzzles. This project's aim is to improve significantly our knowledge and understanding of the flow behaviour of swimming algae in complex flow conditions, in particular in oscillatory flows, mixed shear-extension flows and flows in non-Newtonian media such as viscoelastic suspensions. For this purpose, a type of unicellular algae, Dunaliella Salina, will be examined to determine its swimming capabilities under differing stimuli. The work will be primarily experimentally based, with rheology, microscopy and velocimetry methods as a platform to map out the algae's response. We will use key parameters from the experimental data to go on to inform new models of 'microswimmer' transport and diffusion in complex media, through collaboration with modelling and theory experts.