Experimental system for the prevention of O2- and air contamination during biogas upgrading with phototrophic microalgae

Several alternative biogas purification techniques are currently being examined for increasing the efficiency of the biogas production. Phototrophic microalgal strains have been tested for converting large quantities of CO2 from biogas into algal biomass. However, nearly all studies on blogas upgrading with microalgae resulted in contamination of upgraded gas with O-2 caused by photosynthesis or air due to algal culturing in open ponds. To avoid impurities in upgraded biogas, we tested a discontinuous system at bench scale. We grew the well-studied green algae Chlorella vulgaris and the recently described green algae Chloroparva pannonica in a tubular photobioreactor with 3NBB medium. Subsequently, we used a, detached gas scrubber to transfer CO2 from biogas into dark-adapted microalgal suspensions. During the gas upgrading, the O-2- and CO2 concentrations in biogas were monitored and corresponding reaction kinetics of mass transfer from biogas into algal medium were determined. The upgrading experiments resulted in a virtually complete removal of CO2 from all biogas batches. Simultaneously, no O-2 or air was added to the upgraded biogases. Furthermore, we found varying CO2 kinetics which indicated an algal-specific effect upon the CO2 removal from biogas. These findings proved the suitability of our experimental system for detailed studies on biogas upgrading with phototrophic microalgae, including their culture media. Moreover, we demonstrated the feasibility of bench-scale biogas upgrading with microalgae without simultaneous contamination of the upgraded gas.