Environmental Engineering Reference
In-Depth Information
β-carotene for the nutritional supplement industry (Borowitzka and Borowitzka 1989; Borowitzka
and Hallegraeff 2007).
Dunaliella
is also commercially grown in Israel and India. The blue-green
alga
Spirulina
(
Arthrospira
) is grown in the United States, China, Taiwan, Thailand, and India
(Belay 1997; Hu 2004), the green alga
Chlorella
in Taiwan, Indonesia, Japan, and Germany (Lee
1997), and the green alga
Haematococcus
in the United States, Israel, and Sweden (Cysewski
and Lorenz 2004). A number of other species such as
Chaetoceros
,
Isochrysis
,
Tetraselmis
,
Nannochloropsis
, and
Nitzschia
are also grown around the world as feed for aquaculture species
(Borowitzka 1999b; Muller-Fuega 2004). Although some of these production plants are very
large (e.g., the
Dunaliella
plants in Australia have an area >750 ha), they are still very small
compared with the production plants needed for biodiesel production. For example, a raceway
pond-based production plant producing microalgae with a 40% lipid content at an average daily
productivity of 30 g/m
2
per day would need approximately 75.5 km
2
of ponds to produce 10,000
barrels (1 barrel = 158.987 L) of oil per day. Therefore, the extremely large scale required for
biofuel production using microalgae presents a new and significant challenge (Borowitzka and
Moheimani 2011; Fon Sing et al. 2011).
The production of biofuels from algae needs not only to be technically feasible, but also must
be commercially viable and environmentally sustainable. The actual production costs of these
commercial producers are difficult to obtain; however, the best estimates are given in Table 26.3.
How do these costs compare with the production costs required to produce biodiesel? Current
prices for comparative feedstock for biodiesel are palm oil (~$U.S. 0.40-0.50/kg) and canola/rape
seed oil (~$U.S. 0.60/kg). Assuming that an alga's oil content is approximately 40% of dry weight
(achievable average), then to produce oil at $U.S. 0.50/kg, the algal biomass must be produced at a
cost of less than approximately $U.S. 0.20/kg (Note: This includes harvesting costs, but it does not
include lipid extraction costs). This presents a major challenge for algal oil production for biofuels.
To achieve this cost, reliable high productivities all year round of a biomass with a high lipid content
(at least 30-40% of dry weight) are essential. Furthermore, culture and harvesting systems have to
be constructed and operated at very low cost.
To achieve high biomass productivities, the following key conditions should be met:
• Maximal available sunshine (i.e., as little cloud cover as possible), and
• As little rainfall as possible (because rain means clouds, thus reducing light available, and
for better control of salinity).
taBle 26.3
estimated Production costs of commercially Grown microalgae
estimated Production cost
for dry Biomass in australian
dollars per kilogram
alga
culture system
Place
Dunaliella salina
Extensive (~270 ha) open
ponds
Australia
$6
Chlorella spp.
Open ponds
Taiwan
$17
Open ponds (shallow
cascade system)
Australia
(pilot plant operation)
$15
Spirulina
Open raceway ponds
United States
$15-20
Haematococcus pluvialis
Tubular photobioreactor
Israel
>$50
Several species for
aquaculture
Mainly closed reactors
Australia, United States,
Europe
$50 to >$1000
a
a
Some of the high costs can be attributed to the small scale of the operations.
