0.35-liter PBR cultivation conditions
For 0.35 L PBR operation, the reactors were inoculated with theArthrospira strain grown at 30 °C to a concentration of 0.5 gDW L-1. The pH value was maintained between 9.2-9.8 with an aeration rate of 80 mL min-1 supplying 0.75 % CO2 during the light phase and 0.20 % CO2 in the dark phase for cultures grown at 30 °C and 35 °C. The cultures grown at 20 ° C were supplied with 0.38 % CO2 during the light phase, and 0.2 % CO2 in the night phase. The aeration rate chosen for these experiments is higher than normal due to the filamentous nature ofArthrospira that leads to settling under less stringent conditions. Thus the CO2 concentration, required to supply the cultures and replenish the bicarbonate consumed by the organism, appears low but is confirmed to be sufficient by the pH monitoring, as well as extensive experience with outdoor cultivations. The light regime for the cultures was a 12 h light:12 h dark cycle with light intensity of 230 μmol m-2 s-1from one side of the PBRs using fluorescent lamps (Plusrite). This irradiance level was chosen to model annual average conditions for typical vertical PBR arrays deployed in Fort Myers, Florida. For CO2 aeration and mixing of the cultures, a custom designed porous air diffuser (0.5 mm diameter) was used in order to generate mm-size gas bubbles for aeration at a constant flow rate of 80 mL min-1.