Ra Influence of Liquid/Gas ratio and alkalinity on photosynthetic biogas upgrading efficiency in an outdoors tubular photobioreactor David Marín1, Antonio Ortíz2, Enrica Uggetti2, Joan García2, Raquel Lebrero1, Raúl Muñoz1,* 1 Department of Chemical Engineering and Environmental Technology, Valladolid University. * mutora@iq.uva.es 2 GEMMA-Environmental Engineering and Environmental Group, Universitat Politècnica de Cataluña INTRODUCTION • Biogas from the anaerobic digestion of solid wastes constitutes an important energy source able to decrease the dependence on fossil energy in our current society. • The use of biogas as a substitute of natural gas or fuel in transportation requires an effective purification to levels set by international regulations. Biogas injection into natural gas grids typically requires concentrations of CH4 ≥95%, CO2 ≤2%, O2 ≤0.3% and negligible amounts of H2S. • Algal-bacterial processes have emerged as a cost effective and environmentally friendly alternative for biogas upgrading compared to conventional physical/chemical or biological technologies. • Bahr, M., Díaz, I., Dominguez, A., González Sánchez, A., Muñoz, R., 2014. Microalgal-biotechnology as a platform for an integral biogas upgrading and nutrient removal from anaerobic effluents. Environ. Sci. Technol. 48, 573–581. doi:10.1021/es403596m • Marín, D., Posadas, E., Cano, P., Pérez, V., Blanco, S., Lebrero, R., 2018. Seasonal variation of biogas upgrading coupled with digestate treatment in an outdoors pilot scale algal-bacterial photobioreactor. Bioresour. Technol. 263, 58–66. https://doi.org/10.1016/j.biortech.2018.04.117 • Muñoz R., Meier L., Díaz I. and Jeison D. (2015) A review on the state-of-the-art of physical/chemical and biological technologies for biogas upgrading. Rev. Environ. Sci. Biotechnol. 14:727–759 Aknowledgments: This work was supported by the project INCOVER. The project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the grant agreement No. 689242. MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS Microalgae BioFertilizer H2S CO2 BioCH4 SO4 2- O2 Solar Energy Digestate Organic Waste Anaerobic Digester Biogas CH4 CO2 H2S Aims of this study: • Study the influence of the liquid/gas ratio on the quality of the upgraded biogas. • Evaluate the influence of alkalinity on the absorption column. Two experimental series were conducted: • During the first experimental series, biogas was sparged into the absorption column (AC) under co-current flow operation in order to evaluate the influence of the liquid/gas ratio (L/G). • During the second experimental series, the influence of the alkalinity on the AC was studied. Biogas was sparged into the AC under co-current flow operation with an addition of a carbonate solution (NaHCO3 and Na2CO3) with a concentration of 16000 mg L-1 of inorganic carbon (IC) Experimental Set-up used for this study Evaluation of the liquid/gas ratio in the absorption column L/G Ratio Liquid Volume (L d-1) Biogas Volume (L d-1) 0.5 50 100 1.0 100 100 2.0 200 100 3.0 300 100 4.0 400 100 5.0 500 100 Evaluation of the influence of alkalinity on the absorption column L/G Ratio IC Concentration (mg L-1) Carbonate Solution (L d-1) 0.5 16000 0 1 2 3 5 The increase in the L/G ratio mediated a higher desorption of O2 and N2, which negatively impacted the final concentration of CH4 in the upgraded biogas. REFERENCES • To the best of our knowledge, this research constitutes the first evaluation of the use of microalgae for biogas upgrading under outdoors conditions at a pilot scale. • This research confirmed the key role of the liquid/gas ratio on the biogas upgrading efficiency. • The results herein obtained confirmed the key role of alkalinity on the biomethane quality. Evaluation of the liquid/gas ratio in the absorption column Evaluation of the influence of alkalinity on the absorption column Liquid Recirculation Pump Biogas Pump External Liquid Recirculat