Strategies for decreasing the O2 content in the upgraded biogas purified via microalgae-based technology

Abstract

Microalgae-bacteria consortium based technology using a High Rate Algal Pond (HRAP) interconnected to an Absorption Bubble Column (ABC) has emerged as an environmentally friendly promising option to upgrade biogas. However, the oxygenic photosynthesis of microalgae induces oxygen contamination in upgraded biogas, which could limit its further applications. Several strategies were proposed to favor the oxygen desorption and oxygen uptake in parts and accessories of the upgrading system. The effect of the volumetric ratio liquid recirculation rate/biogas rate (L/G = 5.0, 1.0 y 0.5) was evaluated in conjunction with the application of a novel accessory called Open Trickling Column (OTC). The O2 content in upgraded biogas was around 2.1%v, attaining CO2 removal efficiencies around 90%, at L/G ratio of 1.0 during diurnal and nocturnal periods. The inclusion of an OTC at the previous L/G, enhanced 54% the removal of O2 by stripping and uptake compared with the basal condition. Mass balances of H2S and methane showed that L/G > 1.0 favored the complete oxidation of H2S but promoted the loss of methane in dissolved form. Additionally the effect of increasing linear velocity of liquid broth in the lab-scale HRAP (from 15 cm s−1 to 20 cm s−1) showed to improve the O2 stripping with a consequential increase of biomass concentration under steady-state (from 0.7 to 1.4 g L−1) besides achieving O2 content in the upgraded biogas around 1.5%v.