Mixing algae in a PBR can be carbon positive !! 64Anna Stephenson of University of Cambridge says
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.
Equally interesting is the research being carried out by
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.