Microalgal-bacterial consortium for the removal of volatile methylsiloxanes from biogas in a multi-channel capillary photobioreactor

Abstract

Volatile methylsiloxanes (VMS) are widely occurring biogas contaminants that hinder the performance and lifetime of energy recovery systems. Despite the feasibility of biological VMS removal, important limitations remain, and the use of microalgal-bacterial consortia has not yet been investigated. The present study presents the first assessment of the removal of seven VMS from simulated biogas using a multi-channel capillary pho- tobioreactor (PBR). Chlorella vulgaris was initially used as the sole inoculum, followed by the addition of mixed recirculation sludge, VMS-enriched sludge, and the surfactant Tween 80. C. vulgaris provided CO2 fixation rates up to 302 mgCO2 L 1 d 1 and average total VMS removal and elimination capacity of 36 ± 10% and 1142 ± 436 μg L 1 h 1, respectively. PBR re-inoculation with sludge did not significantly improve the average VMS removal due to gas-liquid mass transfer limitations. The addition of Tween 80 increased the total VMS removal efficiency and elimination capacity to 60 ± 4% and 2136 ± 195 μg L 1 h 1, respectively. This improvement was attributed to enhanced mass transfer of VMS such as D5 (decamethylcyclopentasiloxane) from the simulated biogas to the culture, along with a substantial increase in siloxane adsorption and accumulation in the biomass. The combi- nation of a microalgal-bacterial consortium with a capillary reactor was proved effective for VMS removal, namely in the presence of a surfactant. These findings open new perspectives for the integration of microalgae- based systems and advances PBR designs into biogas upgrading technologies, which are essential to enable the reliable large-scale use of biogas as a renewable energy source.