Influence of the diffuser type and liquid-to-biogas ratio on biogas upgrading performance in an outdoor pilot scale high rate algal pond

Abstract

Four different types of biogas diffusers (metallic of 2 µm, porous stone, and two ceramic membranes of 0.2 and 0.4 µm) were evaluated to improve the quality of biomethane in an outdoor pilot scale photobioreactor interconnected to an external biogas absorption unit. Each type of diffuser was tested independently using three different liquid to biogas (L/G) ratios (0.5, 1 and 2). No significant difference was recorded in the CH4 concentrations of biomethane (i.e. > 93.0%) working with the different types of diffusers at L/G ratios > 1. Only the metallic biogas diffuser supported CH4 concentrations higher than 94.0% at a L/G ratio of 0.5. The increase in L/G ratio induced the stripping of the dissolved N2 and O2 into the biogas, which compensated the decrease in CO2 concentration mediated by the higher pH value of the scrubbing solution. The ANOVA of the results here obtained confirmed that both the type of biogas diffuser and the L/G ratio significantly determined the quality of the upgraded biogas.