Conversion of Biogas to Bioproducts by Algae and Methane Oxidizing Bacteria

摘要

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_2 in a synthetic biogas was photosynthetically fixed by an algae Scenedesmus sp. culture at an average rate of 192 ± 9 mg CO_2 L~(-1) liquid d~(-1), resulting in concomitant O_2 production. After N-depletion, more than 30% of the 220 ± 7 mg lipids g~(-1) total organic carbon were unsaturated. In a second stage, the theoretical resulting gas mixture of 60% CH_4 and 40% O_2 was treated by a methane oxidizing Methylocystis parms culture, with oxidation rates up to 452 ± 7 mg~(-1) CH_4-C L~(-1) liquid d~(-1). By repeated N-limitation, concentrations of 295 ± 50 mg intracellular polyhydroxybutyrate g~(-1) cell dry weight were achieved. Finally, a one-stage approach with controlled coculturing of both microbial groups resulted in harvestable biofiocs. This is the first time that a total microbial conversion of both greenhouse gases into biomass was achieved without external O_2 provision. Based on these results, a biotechnological approach is discussed whereby all kinds of biogas can be transformed into valuable bioproducts.