초록
<P><B>Abstract</B></P> <P>The use of biogas for grid injection or vehicle fuel requires purification steps to obtain biomethane, process normally called biogas upgrading. The use of microalgae cultures has been proposed as a new alternative for CO<SUB>2</SUB> removal from biogas. Full-scale systems for biogas upgrading using microalgae should be able to deal with natural existing day/night photoperiods. This research evaluated the effect of a light/dark photoperiod on the operation of a photosynthetic biogas upgrading system, at lab-scale conditions. A system based on an open-photobioreactor connected to a mass transfer column was used for that purpose. Using a continuous biogas flow, an upgraded biogas with a CO<SUB>2</SUB> concentration between 2 and 4.5% was obtained throughout light and dark periods. O<SUB>2</SUB> concentrations below 1% in final biogas were observed. Mass balances showed that CO<SUB>2</SUB> desorption was the main process behind CO<SUB>2</SUB> removal. CO<SUB>2</SUB> removal during the dark phase was possible, under the tested conditions, as a result of inorganic carbon desorption from the photobioreactor and accumulation in the liquid phase.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Biogas can be upgraded continuously during light/dark cycle using a photobioreactor. </LI> <LI> Desorption from reactor and accumulation as HCO<SUB>3</SUB> <SUP>−</SUP> enabled CO<SUB>2</SUB> removal overnight. </LI> <LI> CO<SUB>2</SUB> desorption was the main mechanism of carbon removal from photobioreactor. </LI> <LI> Temperature decrease during dark-time enhanced CO<SUB>2</SUB> absorption. </LI> </UL> </P>