ISIS Report 03/03/06
Green Algae for Carbon Capture & Biodiesel
A sustainable option overlooked? Prolific green
algae that capture carbon dioxide to make biodiesel.
The article, along with others, will form part of ISIS’ 2006 Energy
Report (see advertisement below) to be submitted to UK government’s energy review.
A fully referenced version of this article is posted on ISIS
members’ website. Details here.
Carbon Capture and Storage mega-project beset with
The UK government has invested in a £25
million Carbon Capture and Storage (CCS) demonstration project led by British
oil company BP as a way of reducing greenhouse gas emissions. This involves
capturing carbon dioxide from the exhausts of power stations and hydrogen or
oil and gas production facilities in a relatively pure form and storing it
geologically underground, in porous layers of rock, depleted or near-depleted
oil and gas fields, deep saline aquifers (porous rock layers containing salty
water deep underground), or in coal seams that cannot be mined.
energy sector is responsible for 35 percent of carbon emissions, so CCS seems
an effective way of tackling the problem head on. UK’s sector of the North Sea
has large storage potential, estimated at ~20 000 to 260 000 Mtonne CO2.
But it is illegal to dump large quantities of CO2 under the North
Sea at the moment. Nevertheless, the Norwegian company Statoil has been
co-produced with natural gas into a deep aquifer overlying its offshore Sleipner
field since 1996, and nothing seems to have leaked from the 6 mt CO2
stored so far. Geologists are continuing to monitor the situation.
already adopted in the North Sea Enhanced Oil Recovery (EOR) programme is to
pump CO2 underground to dissolve in the oil,
making it more mobile and easy to extract. The North Sea Oilfields have an
estimated storage capacity of ~700 Mtonne CO2. UK’s oil
operations are nearing the end of their operation, and EOR could postpone decommissioning
and recover more oil.
However, there are
problems in capturing carbon dioxide economically and without compromising the
efficiency of the power plants. The carbon dioxide captured also has to be
transported to the storage sites, and that could involve thousands of
kilometres of pipelines.
are major concerns over the integrity of the geological storage, the
possibility of leakage during storage and transport, and the potential impacts
on the marine ecosystem when CO2 is injected into
the deep ocean.
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According to the US Department of Energy, CO2 capture is the limiting
factor economically, and is generally estimated to represent 75 percent of the
total cost of CCS.
What no one seems to be aware of is that the humble green algae could offer
a cost-effective and environmentally benign way to capture carbon dioxide on-site
that does not need transport or storage, and at the same time, provides renewable
biodiesel fuel much more effectively and sustainably than energy crops (“Biofuels
for oil addict”, this volume).
Green algae to the rescue
Isaac Berzin, a rocket
scientist at Massachusetts Institute of Technology, is using algae to clean up
power-plant exhaust, saving greenhouse gas emissions and satisfying energy
The idea occurred
to him three years ago, although it is not exactly new (see later). He bolted
onto the exhaust stacks of a 20 MW power plant rows of clear tubes with green
algae soup inside. The algae grew happily, gobbling up 40 percent of the carbon
dioxide for photosynthesis, and as a bonus, 86 percent of the nitrous oxide as
well, resulting in a much cleaner exhaust.
The algae is harvested daily and its oil extracted to make biodiesel for transport
use, leaving a green dry flake that can be further processed to ethanol, also
a transport fuel (but see “Ethanol
from cellulose biomass not sustainable nor environmentally benign”, this
GreenFuel, the company set up by Berzin in Cambridge Mass., has already attracted
£11 million in venture capital funding and is conducting a field trial at 1
000 MW plant owned by a major southwestern power company. GreenFuel expects
two to seven more such demo projects, scaling up to a full production system
One key to success is to select an alga with a high oil density – about 50
percent by weight. Algae are prolific and can produce 15 000 gallons of biodiesel
per acre, compared to just 60 gallons from soybean. Berzin estimates that a
1 000 MW power plant using his system could produce more than 40 million gallons
of biodiesel and 50 million gallons of ethanol a year. But that would require
a 2 000 acre farm near the power plant.
Greenfuel is not alone in racing to make oil out of algae. Greenshift Corporation,
an incubator company based in Mount Arlington New Jersey, licensed a CO2-scrubbing
screen-like filter developed by David Bayless, researcher at Ohio University.
A prototype is capable of handling 140 cubic metres of flue gas per minute,
an amount equivalent to the exhaust from 50 cars or a 3-megawatt power plant.
The US National Renewable Energy Laboratory (NREL) had a research project from1978
to1996 on creating renewable transportation fuel with algae making use of waste
CO2 from coal fired power plants. The project, led by NREL scientist
John Sheehan, was funded at $25.05 m over the 20-year period, compared to the
total spending under the Biofuels Program over the same period of $459 m. It
resulted in a collection of 300 species of green algae and diatoms, now housed
in the University of Hawaii and still available to researchers. Although some
technical and economic problems remained to be solved, it was estimated that
just 15 000 square miles (or 3.8 m ha) of desert (the Sonoran desert in California
and Arizona is more than 8 times that size) could grow enough algae to replace
nearly all of the nation’s current diesel requirements, and algae use far less
water than traditional oilseed crops.
suggested using algae to clean up Salton Sea in Southern
California , into which more than 10 000 tons of nitrogen and phosphate
fertilizers are discharged annually. The idea was to use some 1 000 ha of pond
system to grow algae such as Spirulina
with the sea water, harvest the algae biomass and convert that into fuels,
while the residual sludge could be recycled to agriculture for its fertilizer
value. An estimate suggests that such a process could mitigate several hundred
thousand tons of CO2 emissions at below $10/ton CO2
But it is perhaps the algae’s potential for carbon-capture that makes them
most attractive, and it is as yet almost untapped.