Biomedical Engineering Reference
In-Depth Information
P. cruentum, Scenedesmus obliquus,
and
Synechocystis aquatilis
have been grown
autotrophically in PBRs. Calculations with
Dunaliella
cultures showed that the
use of a large, dense inoculum accelerates cell division with early attainment of
stationary phase (Subba Rao, 2009). Such a shift saves time, which is desirable in
a production process. Without negatively impacting growth rates, it is possible to
attain a twofold increase in biomass in
Neochloris oleoabundans
by sequential
increases in irradiance levels (Wahal and Vjamajala, 2010). Based on the geom-
etry, fluid flow, and illumination on the biomass growth, Wu and Merchuk (2004)
developed a triangular airlift reactor in which removal of CO
2
by two green algae
(
Dunaliella parva
and
D. tertiolecta
) in a pilot-scale unit supplied with flue gases
from a small power plant was 82.3 ± 12.5% on sunny days and 50.1 ± 6.5% on
cloudy days.
The University of California, San Diego, designed a multi-stage algal bioreactor
at the Scripps Institution of Oceanography (http://techtransfer.universityofcalifornia.
edu/NCD/21141.html). This reactor provides light-limited growth, different or com-
bined nutrient-controlled regimes, and can pre-amplify algal production to continu-
ously inoculate existing pond or bioreactor systems.
Ben-Amoz (2009) reported that aeration of mass cultures with CO
2
lue gases
enhances
Dunaliella
production from 2
to 20 g C m
−2
d
−1
and could serve as an ideal
and inexpensive nutrient source in commercial settings. Recent developments have
substantially reduced production costs of microalgal dry biomass from $1,000 kg
−1
in
1953 to a fraction of this ($0.17 to $0.29 kg
−1
) when grown in wastewater (De Pauw
et al., 1984). Israel-based Seambiotic produces
Dunaliella
for $17 kg
−1
dry weight
(DW) and by enrichment with CO
2
lue gases aims to produce
Nannochloropsis
for
$1.00 kg
−1
DW.
To lessen the costs associated with harvesting, Johnson (2009) provided “proof-of-
concept” and cultured
Chlorella
sp. in the laboratory on attached solid polystyrene
substrate on the bottom of a growth chamber. In dairy farm wastewater,
Chlorella
biomass reached production rates up to 3.2 g m
−2
d
−1
, comparable to suspended liquid
cultures, and was harvested easily by scraping the solid surfaces. In addition to
remediation of dairy manure water, an added advantage of this method was that the
attached algal colonies served as inocula and eliminated the extra inoculation step
(Johnson, 2009).
Although heterotrophic cultivation of algae could be cost-effective, only a few
studies have been carried out. Growth of
Chlorella vulgaris
with the addition of the
bacterium
Azospirillum brasiliense
in a heterotrophic regime, using glucose, yielded
growth superior to that in cultures grown in autotrophic and mixotrophic regimes
(Perez-Garcia et al., 2010).
Chlorella protothecoides
has been grown heterotrophi-
cally using an organic carbon source in an enclosed environment of fermenters rang-
ing from 5 to 11,000 L capacity (Li et al., 2007). The PBRs and fermenters have the
advantages of reduced contamination and evaporation, but are more expensive than
open ponds and raceways. They can be utilized in the production of large volumes
of inocula while switching over from an autotrophic mode to heterotrophic mode of
cultivation.
Under the temperate climatic conditions of British Columbia (Canada), calcu-
lated base costs per liter of algal oil from raceways, closed PBRs, and fermenters
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