Development of industrial scale microalgae production

The work concerns large scale production of microalgae in photobioreactors and involves both technical-economic studies, productivity modeling and validation in industrial scale.Chapter 2 is an economical comparison of the 3 major microalgal production technologies: open raceway ponds, tubular photobioreactors and flat panel photobioreactors. The assessment of the operational performance of the three technologies was based on published productivity results from experimental photobioreactor and pilot plant studies. Effects of scale, site and various optimization options were included in a sensitivity analysis.Reducing auxiliar energy requirements for mixing with the two photobioreactor technologies was identified as a major challenge in the development of photobioreactor production of microalgal biomass, particularly for biofuel application. A standard hydraulic examination of auxiliary energy use with tubular- and flat panel photobioreactors was carried out in Chapter 3, resulting in general design recommendations. In chapter 4, a model of microalgal growth as a function of irradiance and temperature was developed in the laboratory and extended with an irradiation model for a specific flat panel reactor. The model was used to optimize the design of the flat panel photobioreactor and was validated in a study of a full-scale installation of the photobioreactor. Chapter 5 and 6 describes the design and development of operating techniques for a tubular photobioreactor for production of microalgal oil, based on recommendations in chapters 2 and 3. A laboratory protocol to compare the suitability for oil production in microalgal strains was developed and a laboratory method to determine the minimum biomass concentration in an outdoor tubular photobioreactor. On the basis of that, two strains, Neochloris oleoabundans and Chlorococcum littorale were selected for further work. A method, the inverse nitrogen quota, was developed to predict and steer microalgal oil production, in terms of total fatty acid content, based on assimilated nitrogen and biomass yield. The method is strains-specific and was completed for the two selected strains. A pilot plant with a 6 m3 tubular photobioreactor was designed and constructed in southern Spain and growth and oil production with the two selected microalgal strains  was  tested.The general discussion includes a resume of the achievements in chapters 2-6 and an analysis of the current stage of development and a future outlook of the microalgal R & D field.  It is noticed that well managed outdoor production trials may match laboratory results in terms of photosynthetic efficiency, but a gap remains between experimental and routine practice. Also, the cost of photobioreactor manufacturing should be reduced. Recent proliferation of the microalgal production sector and public-private development partnerships hold promise that the future may bring cost-competitive microalgal commodity products.