The photobioreactor was connected to a 0.7 L bubbling column operated in counterflow mode. Microalgae culture was continuously circulated between the photobioreactor and the column, by means of a peristaltic pump, in the same way as when operating the system depicted in Fig. 1. Column dimensions were 2.2 m height and 0.02 m diameter. The system was operated injecting real biogas (72 ± 2% CH4; 28 ± 2% CO2) in the bottom of the column. Biogas was produced in a 4.5L lab-scale UASB reactor. The anaerobic digester was operated at 30?C, and fed continuously at an organic loading rate (OLR as COD) of 5 g L?1d?1, using diluted wine as substrate. Samples were periodically taken from the photobioreactor to determine biomass and DIC concentrations. Gas samples were taken from sampling ports located at the entrance and exit of the column for determination of gas composition.