Biological hydrogen production by Anabaena sp. – Yield, energy and CO2 analysis including fermentative biomass recovery

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 H2 production, the energy consumption and CO2 emissions and the technological bottlenecks and possible improvements of the whole energy and CO2 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 kgH2H2/kgbiomass which had a rough energy consumption of 1538 MJ/MJH2H2 and produced 114640 gCO2/MJH2H2. 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 CO2 showing that although the process increased the overall efficiency of hydrogen production it was not a viable energy and CO2 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 kgH2H2/kgbiomass). 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).

► Best H2 photoautotrophic production yield is 0.128 kgH2H2/kgbiomass (Ar + CO2 + N2 gas atmosphere; high intensity of light). ► Best H2 production, energy and CO2 balance is for Ar + CO2 + 20% N2 gas atmosphere and medium light intensity. ► H2 yield can be increased 8% using the biomass leftovers but with 12% energy and CO2 increase. ► Improving H2 yield and using high shares of renewable electricity, allows significant decrease of energy and CO2. ► Cyanobacteria-based production of H2 must be further investigated to be sustainable relevant.