Tubular Photobioreactors

Considerable progress has been made in the past decade in developing the appropriate biotechnology for microalgal mass cultivation aimed at establishing a new agro-industry. However, until today economic constraints currently limit the industrial exploitation of microalgae for feed, food and biofuel production. Largescale tubular reactors are being operated in Germany and Israel for the production of Chlorella and Haematococcus respectively. However, because of their high investment costs and energy requirement (particularly for mixing and cooling) their use is limited to the production of high-value products for human nutrition, cosmetics and pharmaceutical applications, and for the preparation of inocula for industrial production of low value commodities (biofuels). Tubular reactors are mandatory for the cultivation of strains that require a strict control of temperature and for the production of biohydrogen and in general volatile compounds. In this chapter, rather than extensively examining the plethora of photobioreactor designs available in the literature, we focus the attention on the main biological and technological constraints affecting their performance, and in the second part of this chapter we briefl y describe the tubular reactors that are currently operated at a market size. Finally, principles for guiding optimal photobioreactor design are proposed.