Perspectives on third generation gaseous biofuel
Guneratnam, Amita Jacob
University College Cork
Advanced biofuels that have high productivity such as micro and macro algae or certain plant based waste biomass are considered as third generation biofuel. Hydrogen produced using surplus electricity can be then transformed to methane by biological or catalytic methanation is also considered as a candidate for third generation feedstock to produce gaseous biofuel. Micro-algal biomass can be produced using waste exhaust streams from industries containing CO2, SOx, NOx. The emissions from a 1 GWe coal power plant if captured can produce 2.69Mt of micro-algal (volatile solids) in a closed cultivation system with a carbon capture efficiency of 80 %, in a foot print of 19,200 hectare for a tubular photo-bioreactor. Macro-algae (seaweed) can also be produced by sequestering nitrogen from waste streams that are released by fish farms. A production of 168Mt of seaweed integrated with 13Mt of farmed salmon is required if 1.25 % of energy in transport is to be provided by seaweed biomass. However this involves operating 2600 anaerobic digesters, each treating 64,500t/a of S.latisma in coastal digesters. Brown seaweed such as Laminaria digitata was subjected to a two-stage fermentation process that involved hydrolysis followed by methanation. It was found that two stage fermentation of L. digitata can be implemented if shorter retention times and higher organic loading rate are required. Average methane yields of 176 and 234 L/kg VS (two stage) and 221 L/kg VS (single stage) were obtained with higher methane compositions than that of the single stage process. H2 and CO2 were used in ex-situ biological methanation which was conducted at two thermophilic temperatures (55°C and 65°C) with methane compositions of 85–88% and volumetric productivities of 0.45 and 0.4L CH4/Lreactor were observed at 55°C and 65°C after 24h respectively. Methanothermobacter species represent likely and resilient candidates for thermophilic biogas upgrading.
Biofuel , Biogas , Seaweed , Micro-algae , Hydrogen
Guneratnam, A. J. 2017. Perspectives on third generation gaseous biofuel. PhD Thesis, University College Cork.