MATERIALS AND METHODS Biomethane gasometer Raw biogas gasometer 100L Tank Settler Biogas (G) Settled Biomass Liquid Recirculation (L) Domestic wastewater or centrate Raw biogas composition: Biogas upgrading using algal-bacterial processes in wastewater treatment plants M. Rosario Rodero1,3, Raquel Lebrero1,3, Esteban Serrano2, Enrique Lara2, Zouhayr Arbib2, Raúl Muñoz*1,3 1- Department of Chemical Engineering and Environmental Technology, University of Valladolid, Dr. Mergelina s/n., Valladolid 47011, Spain. 2- FCC Servicios Ciudadanos, Av. del Camino de Santiago, 40, edificio 3, 4ª planta,28050 Madrid, Spain 3- Institute of Sustainable Processes, University of Valladolid, 47011, Valladolid, Spain * Author for correspondence: mutora@iq.uva.es INTRODUCTION RESULTS AND DISCUSSION CONCLUSIONS Negligible influence of the hydraulic retention time (HRT) in the HRAP and the biogas flowrate in the absorption column on the biogas upgrading performance. Higher CO2 and H2S removal efficiencies were obtained using centrate instead of domestic wastewater due to the higher alkalinity and pH of the influent. Higher L/G ratios entailed higher CO2 and H2S removals, but an increased stripping of N2 and O2 was observed, which negatively impacted CH4 concentration in the upgraded biogas. To the best of our knowledge, this work demonstrated for the first time the capacity of algal-bacterial systems for the simultaneous biogas upgrading and wastewater treatment at semi-industrial scale. References: [1] Toledo-Cervantes A., Serejo M., Blanco S., Pérez R., Lebrero R., Muñoz R., (2016). Photosynthetic biogas upgrading to bio-methane: Boosting nutrient recovery via biomass productivity control. Algal Res.17, 46-52. [2] Marín D., Posadas E., Cano P., Pérez V., Blanco S., Lebrero R. and Muñoz R. (2018). Seasonal variation of biogas upgrading coupled with digestate treatment in an outdoors pilot scale algal-bacterial photobioreactor. Bioresour. Technol. 263, 58-66 [3] Posadas, E., Serejo, M.L., Blanco, S., Pérez, R., García-Encina, P.A., Muñoz, R. (2015). Minimization of biomethane oxygen concentration during biogas upgrading in algal-bacterial photobioreactors. Algal Res. 12, 221–229. Acknowledgments:The project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 689242. Biogas, which mainly consists of CH4 (40-75%), CO2 (15-60%) and H2S (0.005-2%), constitutes a valuable renewable energy source able to reduce our current dependence on fossil fuels. In this context, H2S removal is mandatory due to its corrosive, malodorous and pernicious nature, while CO2 removal increases the specific calorific value and reduces biogas costs of compression and transportation [1]. Figure 2. Influence of the L/G ratio on biogas upgrading performance at biogas flowrate of 276 (black), 370 (white) and 459 (grey) L h-1 during stage I (a), stage II (b) and stage III (c). Effluent composition DWW, HRT= 3.5 days DWW, HRT = 8 days Centrate, HRT = 73 days COD (mg L-1) 99.4±31.3 65.0±21.7 123.8±0 N-NH4 + (mg-N L-1) 3.1±1.7 1.0±1.1 0±0 N-NO2 (mg-N L-1) 0.8±0.5 0.4±0.2 13.3±11.7 N-NO3 (mg-N L-1) 2.0±1.2 9.6±0.5 38.1±7.4 P-PO4 3- (mg L-1) 1.0±0.5 1.3±0.3 19.9±5.4 Figure 3. Wastewater removal efficiencies in the high rate algal pond during stage I (white), II (black) and III (grey) Table 2. Effluent composition under steady state conditions Objetive: To assess the influence on biomethane composition of: L/G ratio: 1.2, 2.1 and 3.5 Biogas flow rate (G): 274, 370 and 459 L h-1 Parameter Stage I II III Type of wastewater DWW DWW Centrate HRT (d) 3.5 8 73 Average temperature (°C) 23.5±2.5 12.4±2.3 18.8±3.0 Average pH in the cultivation broth 7.3±0.2 7.1±0.5 8.9±0.3 Figure 1. Schematic diagram (left) and photograph (right) of the continuous biogas upgrading experimental plant at Aqualia’s facility in Chiclana CH4 (%) 69.2±4.9 CO2 (%) 32.7±2.8 H2S (ppm) 1183±1006 Biogas upgrading in algal–bacterial photobioreactors re