Supply of CO2 to Closed and Open Photobioreactors

Production of microalgae started in the 1950s at the Massachusetts Institute of Technology producing Chlorella for human consumption using a closed photobioreactor. At the same time, open raceway reactors were used at the University of California, Berkeley, to perform wastewater treatment using microalgae. Since this time, diverse processes have been developed using microalgae to produce valuable products and services. Great efforts were made in the 1980s and 1990s by the Aquatic Species Program in the United States and the RITE project in Japan to develop processes capable of producing biofuels from microalgae. Nevertheless, with the technology available and production costs at the time, it was not possible to compete with petrofuels. Since then, processes for the production of valuable products have been developed such as the production of feed for aquaculture, human nutraceuticals, specialty foods, and carotenoids, among others (Borowitzka 2013). Recently, great interest has emerged in the use of microalgae as CO₂ fixation systems for fossil fuel emissions, thus contributing to the mitigation of GHG emissions, while also producing biofuels. Utilization of microalgae cultures as a CO₂ biofixation method was proposed in the 1960s (Oswald and Golueke 1960); however, this does not amount to a sequestration strategy unless the biomass produced can be stored for any significant time. Thus, one way for 226microalgae to contribute to a reduction in CO₂ emissions is by producing biofuels to replace fossil fuels used today or, alternatively, by allowing the production of other commodities or by-products from flue gases, which provides a net CO₂ benefit in comparison with alternatives, allowing credits for carbon capture systems (Acién et al. 2012a). From several projects, values up to 50 gCO₂/m² · day have been reported, 10 times higher than the capacity of temperate forests (Benemann 1997; Otsuki 2001; Li et al. 2013; Singh and Ahluwalia 2013). However, potential commercial applications are scarce due to high microalgae biomass production costs, applications of microalgae remaining mainly in the markets of human foods and nutraceuticals, in addition to wastewater treatment (Acien et al. 2012b; Craggs et al. 2012; Benemann 2013).