making algal biodiesel in clear tubes has a carbon footprint nearly four times that of producing diesel.
When algae are farmed in perspex tubes, she says, the energy needed to pump the algae around to ensure adequate exposure to sunlight, results in a carbon footprint of 320 grams per megajoule equivalent of fuel.
This compares with 86 g/MJ to extract, refine and burn regular diesel (Energy and Fuels, DOI: 10.1021/ef1003123).
Anna's model shows that growing algae in open ponds offers a lot more potential to produce an environmentally sustainable fuel the footprint of biodiesel produced this way is only 19 g/MJ.
Dont rule out a PBR yet !
Am not sure if Anna Stephenson has taken into account that in open ponds, the water tends to evaporate, and there is the consequent need to keep pumping water.
Prof Mackley and Benjamin Taylor.
Prof Mackley is also incidentally from University of Cambridge, UK.
Their research is about the design and evaluation of an algal oscillatory flow bioreactor (OFB). The design is based on Oscillatory Flow Mixing (OFM).
The goal of their research is to apply OFM technology to develop a more efficient method of algal growth and CO2 sequestration, with one end product being biodiesel.
So, dont rule out a PBR yet.
PBR for commodity products like, biomass, algaefuel, etc is a no go, anyway.
PBR for a speciality high cost end use product is always on. The economics so highly favourable that you can go ahead with OFM or without.
I think for a country such as UK, cultivation through a PBR is the best way to go considering the climatic conditions..
Isn't Anna's research studies a computer model.. I have a few questions.. Has she actually proved DOI's number through her computational approach..
I am trying to get the full paper, any idea where I can get it from??
This is the abstract of the research report.
If you need the entire report you can pay $ 30 for 48 hour access.
" Life-cycle assessment has been used to investigate the global warming potential (GWP) and fossil-energy requirement of a hypothetical operation in which biodiesel is produced from the freshwater alga Chlorella vulgaris, grown using flue gas from a gas-fired power station as the carbon source. Cultivation using a two-stage method was considered, whereby the cells were initially grown to a high concentration of biomass under nitrogen-sufficient conditions, before the supply of nitrogen was discontinued, whereupon the cells accumulated triacylglycerides. Cultivation in typical raceways and air-lift tubular bioreactors was investigated, as well as different methods of downstream processing. Results from this analysis showed that, if the future target for the productivity of lipids from microalgae, such as C. vulgaris, of 40 tons ha−1 year−1 could be achieved, cultivation in typical raceways would be significantly more environmentally sustainable than in closed air-lift tubular bioreactors. While biodiesel produced from microalgae cultivated in raceway ponds would have a GWP 80% lower than fossil-derived diesel (on the basis of the net energy content), if air-lift tubular bioreactors were used, the GWP of the biodiesel would be significantly greater than the energetically equivalent amount of fossil-derived diesel. The GWP and fossil-energy requirement in this operation were found to be particularly sensitive to (i) the yield of oil achieved during cultivation, (ii) the velocity of circulation of the algae in the cultivation facility, (iii) whether the culture media could be recycled or not, and (iv) the concentration of carbon dioxide in the flue gas. These results highlight the crucial importance of using life-cycle assessment to guide the future development of biodiesel from microalgae."
Thanks for the extract. informative.