초록
<P>Biogas produced by anaerobic digestion is typically converted into electricity and low value heat. In this study, biogas is microbially transformed into valuable bioproducts. As proof of principle, the production of feed additives, i.e. lipids and polyhydroxybutyrate, out of biogas was evaluated. In a first stage, the CO<SUB>2</SUB> in a synthetic biogas was photosynthetically fixed by an algae <I>Scenedesmus</I> sp. culture at an average rate of 192 ± 9 mg CO<SUB>2</SUB> L<SUP>–1</SUP> liquid d<SUP>–1</SUP>, resulting in concomitant O<SUB>2</SUB> production. After N-depletion, more than 30% of the 220 ± 7 mg lipids g<SUP>–1</SUP> total organic carbon were unsaturated. In a second stage, the theoretical resulting gas mixture of 60% CH<SUB>4</SUB> and 40% O<SUB>2</SUB> was treated by a methane oxidizing <I>Methylocystis parvus</I> culture, with oxidation rates up to 452 ± 7 mg<SUP>–1</SUP> CH<SUB>4</SUB>–C L<SUP>–1</SUP> liquid d<SUP>–1</SUP>. By repeated N-limitation, concentrations of 295 ± 50 mg intracellular polyhydroxybutyrate g<SUP>–1</SUP> cell dry weight were achieved. Finally, a one-stage approach with controlled coculturing of both microbial groups resulted in harvestable bioflocs. This is the first time that a total microbial conversion of both greenhouse gases into biomass was achieved without external O<SUB>2</SUB> provision. Based on these results, a biotechnological approach is discussed whereby all kinds of biogas can be transformed into valuable bioproducts.</P><P><B>Graphic Abstract</B><BR><IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2012/esthag.2012.46.issue-24/es303929s/production/images/medium/es-2012-03929s_0003.gif'></P>