**Figure 10.**

*Algae raceway pond: The microalgae culture broth is constantly kept in motion with a powered paddle wheel [23].*

surface area for the interaction of light and the algal cells, increasing the time of gas mass transfer in the culture broth, and the efficient uptake of nutrients. Most times, commercial cultivation of microalgae in vertical reactor systems and reactors of other configurations is not economically viable in batch mode, due to the time taken to load, unload, and clean the reactor systems. The vertical tubular reactor can be made of alveolar panels, polyethylene sleeves, or glass tubes and supported on steel frames (see **Figure 11**). The low productivity characterizing this reactor system is overcome when the surface area to volume ratio is increased. The O2 gas mass transfer is aided by bubbling air through the culture broth [23].
