In tubular photobioreactors micro-algae continuously experience dynamically changing oxygen and light conditions when circulating from the solar receiver to the dark degasser. These changes in oxygen concentration and light were simulated in a CSTR using sub-saturating light intensity. Elongation of the residence time in the solar receiver from 30 to 300 min was also investigated. Specific growth rates measured at constant low oxygen concentration PO2 = 0.21 bar were; 1.14 ± 0.06 day 1 using continuous light 0.80 ± 0.16 day 1 with 30 min light and 1.09 ± 0.05 day 1 with 300 min light. The effect of dynamically changing oxygen concentrations from PO2 = 0.21 to 0.63 bar followed by degassing resulted in similar specific growth rates. The exposure of the algae cells to dark periods in the degasser has a bigger negative impact than the temporary exposure to accumulating oxygen concentrations in the solar receiver. This shows that considerable energy savings for degassing are possible.
- tubular photobioreactor