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Influence of liquid-to-biogas ratio and alkalinity on the biogas upgrading performance in a demo scale algal-bacterial photobioreactor

Marín, David, Ortíz, Antonio, Díez-Montero, Rubén, Uggetti, Enrica, García, Joan, Lebrero, Raquel, Muñoz, Raúl
Bioresource technology 2019 v.280 pp. 112-117
absorption, alkalinity, biogas, carbon dioxide, hydrogen sulfide, methane, natural gas, photobioreactors
The influence of the liquid-to-biogas ratio (L/G) and alkalinity on methane quality was evaluated in a 11.7 m³ outdoors horizontal semi-closed tubular photobioreactor interconnected to a 45-L absorption column (AC). CO₂ concentrations in the upgraded methane ranged from <0.1 to 9.6% at L/G of 2.0 and 0.5, respectively, with maximum CH₄ concentrations of 89.7% at a L/G of 1.0. Moreover, an enhanced CO₂ removal (mediating a decrease in CO₂ concentration from 9.6 to 1.2%) and therefore higher CH₄ contents (increasing from 88.0 to 93.2%) were observed when increasing the alkalinity of the AC cultivation broth from 42 ± 1 mg L⁻¹ to 996 ± 42 mg L⁻¹. H₂S was completely removed regardless of the L/G or the alkalinity in AC. The continuous operation of the photobioreactor with optimized operating parameters resulted in contents of CO₂ (<0.1%–1.4%), H₂S (<0.7 mg m⁻³) and CH₄ (94.1%–98.8%) complying with international regulations for methane injection into natural gas grids.