Biological hydrogen production by Anabaena sp. – Yield, energy and CO 2 analysis including fermentative biomass recovery

Abstract

This paper presents laboratory results of biological production of hydrogen by photoautrotophic cyanobacterium Anabaena sp. Additional hydrogen production from residual Cyanobacteria fermentation was achieved by Enterobacter aerogenes bacteria. The authors evaluated the yield of H 2 production, the energy consumption and CO 2 emissions and the technological bottlenecks and possible improvements of the whole energy and CO 2 emission chain. The authors did not attempt to extrapolate the results to an industrial scale, but to highlight the processes that need further optimization. The experiments showed that the production of hydrogen from cyanobacteria Anabaena sp. is technically viable. The hydrogen yield for this case was 0.0114 kg H 2 /kg biomass which had a rough energy consumption of 1538 MJ/MJ H 2 and produced 114640 gCO 2/MJ H 2 . The use of phototrophic residual cyanobacteria as a substrate in a dark-fermentation process increased the hydrogen yield by 8.1% but consumed 12.0% more of energy and produced 12.1% more of CO 2 showing that although the process increased the overall efficiency of hydrogen production it was not a viable energy and CO 2 emission solution. To make cyanobacteria-based biofuel production energy and environmentally relevant, efforts should be made to improve the hydrogen yield to values which are more competitive with glucose yields (0.1 kg H 2 /kg biomass). This could be achieved through the use of electricity with at least 80% of renewables and eliminating the unessential processes (e.g. pre-concentration centrifugation).