Hybrid Photobioreactors, Containing Microstructured Optical Fibres Aimed at Operating with Microalgae (OPTIC-ALGAE)
Microalgae are currently employed in such diverse fields as agriculture, wastewater treatment, aquaculture, bioremediation and manufacture of fine chemicals. Among the later, it is worth mentioning manufacture of such polyunsaturated fatty acids as eicosapentaenoic and docosahexaenoic acids — which are in high demand by the market; these fatty acids bring about health benefits to the human organism, so they can be utilized by the food industry, as functional ingredients. However, as happens with other fine chemicals, economic feasibility of their industrial manufacture is dependent on their production costs — which in turn depend on reactor efficiency. Hence, one major challenge to the current autotrophic microalgal cultivation at the industrial scale is to devise and develop cultivation systems that are more efficient, and thus economically sustainable. Despite several research efforts developed to date, there is no such thing as “the best reactor system” — defined as the one able to achieve maximum productivity with minimum operation costs, for every type of objective function; in fact, choice of the most suitable system is situation-dependent — as both the species of microalga available and the final purpose intended play a role. The need of accurate control impairs general use of open-system configurations, so current investigation has focused mostly on closed systems.
In attempts to improve metabolic efficiency in closed photosynthetic reactors, availability of light and CO2 are often considered as limiting factors — as they are difficult to control in the culture medium. The carbon source to microalgae is usually provided via bubbling of CO2- enriched air into the culture medium; however, this procedure is not particularly effective in terms of mass transfer. Besides, it leads to considerable waste of that gas to the open atmosphere, which adds to operation costs. Hence, increases in the interfacial area of contact available for gas exchange, via use of membranes, might constitute a useful alternative. In fact, use of microporous hollow fibres — rather than plain bubbling, for transfer of CO2 into microalgal cultures, offers technological enhancements in effectiveness of mass transfer. However, when using those devices, the supplies of light and gas are hardly synchronized — so the microalga is not able to fully metabolise the gas supplied. Therefore, the possibility of using optical fibres to introduce light inside heavily packed reactors will likely constitute a breakthrough — that may eventually turn closed reactors into fully competitive options. A combination of porous hollow fibres and optical fibres — in a hybrid fashion, is thus susceptible of leading to substantial increases in the efficiency of use of light and CO2.
An optical fibre consists of a cylindrical core, surrounded by a cladding. During manufacture of the fibre, certain impurities are deliberately introduced in the core and/or the cladding — so that the refractive index is slightly higher in the core than in the cladding; the resulting higher refractive index of the core enables light to be guided by the core, and thus propagate through the fibre. On the other hand, microstrutured fibres are optical fibres, whose waveguiding mechanism and properties are defined by an array of air holes that run down the entire fibre length. They are constructed by stacking silica glass capillaries and rods, and by drawing this composite into optical fibre form. Therefore, this type of fibre enables not only remote illumination, but also allows channelling of liquids and gases. These types of fibres will be extensively tested.
It is expected that this research work will go deeper in the production of biomass and specific metabolites (using polyunsaturated fatty acidsas model system), in an economically attractive mode, via development of novel hybrid photobioreactors.
- Prof. Dr António B. Lobo Ribeiro (Consultant to coordinator)
- Escola Superior Biotecnologia ESB-UCP, Portugal
- Escola Superior Biotecnologia ESB-UCP, Portugal (Coordinator)
- INESC-Porto, Centro de Biotecnologia e Química Fina, Portugal (CBQF/ESB/UCP)
Project supported by:
- Fundação para a Ciência e a Tecnologia