16 2 The influence of biogas flow rate (0, 0.3, 0.6 and 1.2 m 3 m -2 h -1 ) on the elemental and 17 macromolecular composition of the algal-bacterial biomass produced from biogas upgrading in a 18 180 L photobioreactor interconnected to a 2.5 L external bubbled absorption column was 19 investigated using diluted anaerobically digested vinasse as cultivation medium. The influence of 20 the external liquid recirculation/biogas ratio (0.5 < L/G < 67) on the removal of CO2 and H2S, 21and on the concentrations of O2 and N2 in the upgraded biogas was also evaluated. A L/G ratio of 22 10 was considered optimum to support CO2 and H2S removals of 80% and 100%, respectively, at 23 all biogas flow rates tested. Biomass productivity increased at increasing biogas flow rate, with a 24 maximum of 12±1 g m -2 d -1 at 1.2 m 3 m -2 h -1 , while the C, N and P biomass content remained 25 constant at 49±2%, 9±0% and 1±0%, respectively, over the 175 days of experimentation.

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Abstract. 16A pilot high rate algal pond (HRAP) interconnected to an external CO 2 −H 2 S absorption 17 column via settled broth recirculation was used to simultaneously treat a synthetic 18 digestate and to upgrade biogas to a bio-methane with sufficient quality to be injected 19 into natural gas grids. An innovative HRAP operational strategy with biomass 20 recirculation based on the control of algal-bacterial biomass productivity (2. Introduction.

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