The cultivation process relies on photosynthesis. One of the major products from photosynthesis is oxygen; thus as the algae consumes carbon dioxide and photosyn — thesise, the culture experiences a significant increase in dissolved oxygen concen­tration. As mentioned above, excess dissolved oxygen within the culture can inhibit photosynthesis and cause photo-oxidative damage to cells. Molina Grima et al. [22] found that the maximum dissolved oxygen concentration within the culture should not exceed the standard air saturation of the culture by more than 400%. This param­eter constraint is one key issue involved with the scale-up of photobioreactors. Dissolved oxygen cannot be removed within the solar receiver, thus limiting the length of the tubular receiver.