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.

Innovative operational strategies in photosynthetic biogas upgrading in an outdoors pilot scale algal-bacterial photobioreactor

“…In addition, the presence of aerobic conditions likely supported the growth of methanotrophs, which prevented CH4 emission from the cultivation broth in the photobioreactor (Muñoz et al, 2015;Serejo et al, 2015). The biogas upgrading performance here achieved was superior to that reported by Marín et al, (2020), who observed CH4 concentrations up to 94.6% in a similar outdoors experimental set-up without greenhouse during autumn at a L/G of 1. The CH4 concentrations obtained in the upgraded biogas also fulfilled with the current legislation on the use of biogas (European Committee for Standardization, 2018Standardization, , 2017Muñoz et al, 2015).…”

Innovative technologies for biogas upgrading

“…In addition, the presence of aerobic conditions likely supported the growth of methanotrophs, which prevented CH4 emission from the cultivation broth in the photobioreactor. The biogas upgrading performance here achieved was superior to that reported byMarín et al, (2020), who observed CH4 concentrations up to 94.6% in a similar outdoors experimental set-up without greenhouse during autumn at a L/G of 1. The CH4 concentrations obtained in the upgraded biogas also fulfilled with the current legislation on the use of biogas (European Committee for Standardization, 2018, 2017;.…”

Anaerobic Digestion of Food Waste Coupled with Biogas Upgrading in an Outdoors Algal-Bacterial Photobioreactor at Pilot Scale

“…Similarly, N 2 concentration in biomethane during stages I and II averaged 4.2 ± 0.4%. However, the increase in the L/G ratio in stage III mediated an increase in N 2 concentration in biomethane up to 9.4 ± 0.7% as a result of the enhanced dissolved N 2 stripping at higher liquid flowrates [51]. Finally, the resumption of the L/G ratio to 2 in combination with the increase in IC concentration of the culture broth and pH through stages IV and V entailed a decrease in N 2 concentration in the biomethane to average values of 5.3 ± 1.0% (Fig.…”