Biomedical Engineering Reference
In-Depth Information
N fertilizer
P fertilizer
Electrical power
Perspex tubing
N fertilizer
P fertilizer
Electrical power
Concrete walls
Steel paddle
wheel
PVC lining
Water supply &
treatment
FIGURE 9.2 (See color insert.)
The relative contribution of fossil energy (left) and GWP
(right) to the total requirements for microalgal biodiesel production using a tubular airlift
reactor (upper) and a raceway (lower). From the LCA of
C. vulgaris
conducted by Stephenson
et al. (2010) under standard conditions. The total fossil energy requirements of 230 and 29 GJ
and GWP of 13,550 and 1,900 kg CO
2
per tonne biodiesel formed were estimated for the
tubular reactor and raceway, respectively.
9.3.3 n
utrient
p
rovision
For
M
iCroalGal
C
ulture
CO
2
provision to raceway ponds through additional sparging of compressed CO
2
contributed some 40% of the energy consumption and 30% GHG emissions
(Clarens et al., 2010). Alternatively, co-location with industries or facilities with high
CO
2
emissions (such as power stations, fermentation plants, or anaerobic digester
systems) may facilitate reduced contributions for effective CO
2
provision. This
has been demonstrated; however, it is noted that the CO
2
source may influence the
productivity achieved and interacts with the supply of other nutrients. Stephenson
et al. (2010) modeled the impact of CO
2
concentration in the gas to be compressed
for sparging into either the raceway or tubular reactor system. Owing to the influence
of CO
2
concentration on both concentration driving force (and hence transfer rate)
and on the volume of gas to be compressed, its impact is significant, with the fos-
sil energy requirement nearly doubling on decreasing the CO
2
concentration from
12.5% (typical of flue gases) to 9% and increasing fourfold on decrease to 5% by
volume in the raceway system. The design of a low-depth carbonation sump also
favors reduced energy consumption.
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