Part 2.
http://biopact.com/2007/01/in-depth-look-at-biofuels-from-algae.html
Friday, January 19, 2007
An in-depth look at biofuels from algae - 2
The main conclusions of the extensive experimental program were
interesting. They included:
1. Productivities of 15 to 25 g/m2/d were routinely obtained during
the 8-month growing season at this location. However, higher numbers
were rarely seen. Algae were not grown during winter months.
2. Continuous operations are about 20% more productive than
semi-continuous cultures, but the latter densities are much higher, a
factor in harvesting.
3. Culture collection strains fare poorly in competition with wild types.
4. Temperature effects are important in species selection and culture
collapses, including grazer development.
5. Nighttime productivity losses increased to 10% to 20 % in July,
when grazers were present; nighttime respiratory losses were high
only at high temperatures.
6. There is a significant decrease in productivity in the afternoons,
compared to the mornings, in the algal ponds.
7. Oxygen levels can increase as much as 40 mg/L, over 450% of saturation, and
high oxygen levels limit productivity in some strains but not others. Oxygen
inhibition was synergistic with other limiting factors (e.g., temperature).
[...]
9. Mixing power inputs were small at low mixing velocities (e.g., 15
cm/s) but increased exponentially. Productivity was independent of
mixing speed.
10. The strains investigated in this study did not exhibit high lipid
contents even upon N limitation.
11. The transfer of CO2 into the ponds was more than 60% efficient,
even though the CO2 was transferred through only the 20-cm depth of
the pond.
12. Harvesting by sedimentation has promise, but was strain specific
and was increased by N limitation.
13. Initial experiments demonstrated that media recycle is feasible.
14. Project end input operating costs for large-scale production (at
$50/mt of CO2, 70% use efficiency, etc.) was $130/mt of algae, of
which half was for CO2 and one-third for other nutrients, with
pumping and mixing power only about $10/mt.
This project answered a number of issues that had been raised about
this process. One initially controversial observation was the finding
that mixing speed had no effect on productivity. However, this
experiment used a strain of Chlorella that did not settle, and care
was taken to keep other parameters identical (in particular pH and
pO2 levels). Thus, the increased productivities seen in some
experiments (e.g., those of Hawaii), could possibly be accounted for
by differences other than those of mixing, such as changes in
outgassing of O2.
From the perspective of large-scale biomass production, one
conclusion from this research was that
"mixing power inputs make any mixing speed much above about 30 cm/s
impractical, as the energy consumed would rapidly exceed that
produced. The rate of mixing should only be between about 15 and 25
cm/s, sufficient to keep cells in suspension and transfer the
cultures to the CO2 supply stations in time to avoid C limitations in
large-scale (>1-ha) ponds." [181]
For low-cost production higher productivities would reduce capital,
labor, and some other costs, but nutrient (e.g., CO2) related costs
would not change. This suggested the need for low-cost CO2, and other
nutrients, as well as a high CO2 utilization efficiency. Efficient
utilization of CO2 appeared feasible based on the results obtained
with even this unoptimized system.
Another major conclusion was that
"competitive strains would be required to maintain monocultures. The
need for feedback from the outdoor studies to development of
laboratory screening protocols was a major recommendation.
Specifically, the relatively controllable parameters of CO2, pH, and
O2 were of interest in determining species survival and culture
productivity. Also, harvesting was identified as a specific area for
further research. Finally, lipid induction remained to be
demonstrated."[182]
These were the general objectives during the final year of this project.
In 1985-86, numerous microalgal strains were obtained from the SERI
Culture Collection and tested in small-scale, 1.4-m2, ponds. All
strains could be grown quite successfully in these very small units,
although some, such as Amphora sp., did not survive more than 2 or 3
weeks before they were displaced by other algae.
Cyclotella displaced Amphora under all conditions tested, even though
Amphora was the most productive strain, producing 45 to 50 g/m2/d in
very short-term experiments. The green algae, e.g. Chlorella or
Nannochloropsis, also could not be grown consistently. Their
productivities were among the lowest, about 15 g/m2/d (similar to
that in the prior year).
"Thus, one fundamental conclusion was that productivity is not
necessarily correlated with dominance or persistence." [185]
A significant factor in pond operations was the oxygen level reached
in the ponds, which influenced productivity and species survival.
Ponds were operated with air sparging (and antifoam) to reduce DO
levels, from typically 400% to 500% of saturation without air
sparing, to 150% to 200% of saturation with sparging. Foaming, caused
by air sparging, was still was a problem in some cases, as with the
Cyclotella. However this alga exhibited approximately the same
productivity with or without sparging despite the 20%-30% opaque foam
cover, suggesting some positive effect of the lower pO2. For other
algal species productivity differences of 10% to 20% were noted, and
for some (e.g., C. gracilis), no specific effect of high versus low
DO was noted.
These outdoor results were reproducible enough to detect differences
of greater than about 10% between treatments. The major result of
this project was that productivities were 50% to 100% higher than the
previous year, with some species of diatoms producing 30 to 40 g/m2/d
(AFDW, efficiency about 6% to 9% of PAR, or 3% to 4.5% total solar).
The green algae were, as mentioned earlier, less productive than the
diatoms.
A more detailed study of oxygen effects was also carried out in the
laboratory, avoiding the confounding factors of CO2 supply,
temperature, and light intensity. In general the diatoms were
insensitive to high DO; most, but not all, of the green algal strains
exhibited marked inhibition by high oxygen levels:
"None of the oxygen-sensitive algae could be grown outdoors,
suggesting this as a major factor in species dominance and
productivity." [185]
Laboratory studies were also carried out at both high light intensity
and high DO, to determine the synergism between these factors. Both
the apparent maximum growth rate and dense culture productivity were
determined for comparisons. Higher levels of DO intensified the
inhibitory effects of higher light observed in some cases. This was
true in particular for productivity, with growth rates also affected.
Of course, the actual density of the culture is a major factor
determining productivity, and dense cultures avoid most, if not all,
the deleterious effects of high
light intensity. High O2 and low CO2 are other factors influencing
the response to high light, with O2 being more inhibitory at both low
CO2 and high light levels. High oxygen also affects chlorophyll
content, although this effect is most pronounced at low light
intensities where chlorophyll levels are 50% higher compared to high
light intensities.
Outdoor experiments were carried out to determine the effect of low
CO2 (25 µM) and high (9-10) pH, which would be experienced in algal
mass cultures, at least temporarily. Compared to the control
cultures, one strain was not inhibited even at pH 10, two not at pH
9, and two were inhibited by about 33% at this pH, compared to the
control at pH 8. Lowering pCO2 also resulted in similar levels of
inhibition for the other strains. A role for bicarbonate in growth at
high pH was established from the data, with metabolic costs estimated
at about one-third of productivity, a major factor. This requires
further investigation.
One strain, a Cyclotella species, exhibited an increase of lipid
content of more than 40% of dry weight upon Si limitation. However,
lipid productivity (9 g/m2/d), was not significantly different
between Si-deficient and the Si-sufficient controls, because of the
high productivity of the Si sufficient culture. Optimizing for lipid
productivity was considered possible, but requires more detailed
study.
Perhaps most important, the data and simulations also suggest that
maximizing productivity at an acceptable CO2/pH combination from the
perspective of outgassing and CO2 loss from the ponds is possible,
with operations above pH 8.0 required (for an alkalinity of 32 meq/L,
higher for higher alkalinities) to avoid wasting of CO2.
Laboratory studies were also carried out during this project. These
included a study of light conversion efficiencies that concluded that
at low light intensities very high light conversion efficiencies can
be achieved (near the theoretical maximum of about 10 photons/CO2
fixed).
However, these and other laboratories studies carried out during this
project would require a much longer review than possible here.
Note on costs: An important note on costs is required here: the
California project investigated different harvesting techniques for
microalgae cultures. To enhance algae settling, both polymers, FeCl3
and cross-flow filtration were studied. The flocculation technique
(getting the algae to flock together so they can be harvested easily)
required the addition of organic flocculants at about 2 to 6 g/kg and
FeCl3 at about 15 to 200g/kg of algal biomass to remove 90% or more
of the algal cells. Because of the high cost of the organic
flocculants, costs were comparable for both flocculants tested. The
organic polymers were also deemed to have significant potential for
improvement and optimization. Cross-flow filtration, though
effective, was estimated to be too expensive. In short, a
considerable amount of costly inputs is needed to harvest the algae.
No lifecycle study was ever presented which included all these costs
and the energy balances of the inputs.
In conclusion, this project significantly advanced the state-of-the
art of microalgae biomass production, and provided the basis for the
Outdoor Test Facility, the ASP's final project.
ISRAEL
In the mid-1980s, the ASP researchers collaborated with scientists in
Israel, in three separate projects. All these experiments involved
the same idea: growing algae in (very small) open ponds in the
desert. It would take us too far here to discuss the results of these
projects, but for basic data, we refer to Table 1, which presents an
overview of all the field trials initiated under the ASP.
Some key findings included:
-the fact that in chemostat tests (these are lab tests) "nitrogen
limitation does not induce the production and accumulation of
lipids," but the "algae attain a low protein-carbohydrate ratio."
Previous reports in the literature describing lipid accumulation in
algae induced by N limitation were attributed to trace element
limitations.
-two cultures, C. gracilis and Nannochloris atomus grown in
laboratory chemostats and in 0.35-m2 outdoor "microponds" attained
productivities of 40 g/m2/d (C. gracilis) during June-August, which
decreased by a bout half during the winter. Lipid contents in the
N-sufficient algal cells increased almost as much, reproducing the
low-temperature effect on lipid content seen in the laboratory
cultures.
-attempts were also made to increase lipid production by Si
limitation, but this was unsuccessful due to rapid contamination with
green algae.
NEW MEXICO, OUTDOOR TEST FACILITY, 1987-1990
After the above noted projects carried out in Hawaii, Israel and
California, the ASP decided to hold a competition for the development
of a larger process development outdoor test facility (OTF) located
in the southwestern United States. Two independent designs and
proposals were commissioned, one consisting of enclosed production
units; the other of open ponds, similar to the design tested in
California.
The latter design won the competition, with a proposed facility
consisting of two 1,000-m2 ponds, one plastic lined and another
unlined, as well as supporting R&D using six small, 3-m2 ponds,
continuing and extending the work carried out in the prior projects
in California.
Although the proposal recommended establishing this facility in
Southern California, the ASP selected a site in Roswell, New Mexico
to establish the OTF. The project was located at an abandoned water
research facility. Roswell has high insolation, abundant available
flatland and supplies of saline groundwaters. The primary limitation
of this site was temperature, which, in retrospect, turned out to be
too low for more than 5 months of the year for the more productive
species identified during the prior project.
The objective of the first year of the research at this new site was
to initiate a species screening effort at this site with the small
3-m2 ponds, which were installed while designing and constructing the
larger facility. A major objective of this project was to identify
cold weather adapted strains. Building the large system required
installation of two water pipelines of 1,300-m in length (15 and 7.5
cm, for brackish and fresh waters). The ponds were about 14 x 77 m,
with concrete block walls and a central wooden divider. The paddle
wheels were approximately 5-m wide, with a nominal mixing speed of 20
cm/s, and a maximum of 40 cm/s. Carbonation was achieved with a sump
that allowed counterflow injection of CO2, to achieve high (90%+)
absorption of CO2. One pond was plastic lined; the other had a
crushed rock layer. The walls were cinder block. A 50-m2 inoculum
production pond was included.
During the first year of the project (Weissman et al. 1988), all
experimental work was carried out using the small ponds, which
allowed essentially fully automatic operation and continuous
dilution, as well as heating if needed. The objectives were to
determine long-term productivity and stability for this site with
previously studied and new species. Five of the strains inoculated
into the 3-m2 ponds were successfully cultivated, including two that
derived from local isolates (one of which had invaded these ponds).
Three of the culture collection strains could not be cultivated
stably in the small ponds.
"Productivities in the summer month of August reached 30 g/m2/d for
C. cryptica CYCLO1, but decreased to about half this level in
September and October. At this point, M. minutum (MONOR2) was used,
as this is a more cold-tolerant organism. By November productivity of
MONOR2 fell to about 10 g/m2/d, and was very low (3.5 g/m2/d) in
December in unheated ponds. Remarkably, despite these ponds freezing
over repeatedly, the culture survived and exhibited some
productivity." [195]
During August and September, productivities for CYCLO1 and Amphora
sp. exhibited short-term excursions above 40 g/m2/d. Faulty data are
not suspected.
The large-scale system was completed by the second year. But some
problems were encountered: the spongy clay at the site did not
compact well, resulting in an uneven pond bottom. This made it
difficult to clean and drain the ponds, and resulted in settling and
sedimentation of solids.
Significant differences were noted between the lined (north) and
unlined (south) ponds, in terms of mixing velocities, head losses,
and roughness coefficients.
Conclusions for the OTF project
The final report in this series on the New Mexico OTF operations,
reported on the demonstration of productivity for the two large ponds
for 1 full year, continuation of the small-scale pond operations, and
improvements in mixing and carbonation.
1. One major improvement in the system was an automated data
recording and operations system.
2. Mixing was improved by improving the flow deflectors and
increasing operating depths from 15 to 22.5 cm, which is probably a
better depth for large-scale systems.
3. Culture instability was a problem, particularly in spring because
of greater temperature fluctuations, and resulted in low average
productivity of only 7 g/m2/d for March through May. In contrast, the
average productivity was 18 g/m2/d for June through October,
decreasing to 5-10 g/m2/d in November (depending on onset of cold
weather), and only about 3 g/m2/d in the winter months. Overall
productivity, including 10%-15% down-time for the ponds for repairs
and modifications, was 10 g/m2/d, only one-third of ASP goals.
4. A major conclusion from this work is that scale-up is not a
limitation with such systems. Climatic factors are the primary ones
that must be considered in their siting.
5. A countercurrent flow injection system was installed in the sumps
resulting in a carbonation system that was essentially 100% efficient
in CO2 transfer. Overall CO2 utilization was higher than 90%.
6. Species stability in the lined and unlined pond exhibited no
significant difference. This work clearly established the feasibility
of using unlined ponds in microalgae cultivation. This was a critical
issue, as plastic lining of ponds is not economically feasible for
low-cost production.
7. In the small 3-m2 systems, two variables were investigated: Si
supply and pH. Both are major cost factors in pond operation, due to
sodium silicate costs and CO2 outgassing. They affect overall
productivity as well as lipid production. For Cyclotella, for
example, productivity was about 20 g/m2/d at pH 7.2 or 8.3, but only
15 g/m2/d at pH 6.2. As the higher pH range is preferred, where CO2
outgassing is minimal, this demonstrates the feasibility of operating
such cultures within the constraints of a large-scale production
system. Si additions could be halved with only a modest decrease in
productivity, suggesting that Si supply could be reduced,
particularly if low Si-containing diatoms are cultivated. Also Si
limitation can be used to induce lipid production, as was
demonstrated during this project, with lipid biosynthesis increasing
as soon as intracellular Si content dropped, with a 40% lipid content
being achieved. However, overall, lipid productivity did not increase
as CO2 fixation limitation also set in. This remains as a major issue
for future research.
Algae versus tropical energy crops
Tropical energy crops are known for their high biomass
productivities. They come in different forms (grasses, trees, annual
and permanent crops) and under such names as eucalyptus, Arundo
donax, sorghum, sugarcane, oil palm, sweet potato, cassava or sago.
The ASP produced very few field trials in which algae were
successfully grown continuously for periods of over a year. In fact,
most experiments lasted a few days or weeks only (see table 1). Since
algae are highly sensitive to changes in temperature, monthly or
weekly biomass productivity data (e.g. high yields during summer
months) can not be extrapolated into yearly data. Only two series of
data allows us to make a comparison with the yields of tropical
crops. They are the data reported in the "large scale" study of
1977-79 and the data from the OTF trials in New Mexico.
Table 4 shows that tropical energy crops yield considerably larger
amounts of biomass than algae cultures. Several crops easily produce
twice the amount of biomass.
It should be noted that the data for the tropical crop yields in
Table 4 refer to the "phytomass" of those crops. That is the entire
biomass of the plants (including roots or rhizomes). Still for the
majority of these crops (the exception being Arundo donax), the bulk
of this phytomass is actually harvesteable and can be used as a
bioenergy feedstock.
Besides differences in yields, some broad points for comparisons
between algae production systems and 'traditional' terrestrial
agriculture are the following:
-species control and scale:
algae cultures tend to be unstable and can be colonized fairly easily
by more powerful algae; these biologically stronger species are not
necessarily suitable for biofuel production (e.g. their lipid
contents are too low). Now in traditional tropical agriculture, pest
and diseases are a comparable problem: a plantation or a sugarcane
field can be invaded with weeds or pests. But relatively simple
techniques (pesticides, herbicides and phytopathological strategies
using natural predators) can be applied to the crops. In open algae
ponds this would be extremely difficult.
Moreover, experience with terrestrial agriculture has allowed farmers
to estimate the disease, pesticide and herbicide infestation risks
involved in establishing vast monocultures. For algae, the largest
facilities ever usedhad a surface of a mere 0.1 hectares, with most
of them being "micro-ponds" of a few square metres. No studies or
projections exist that allow algae-culturalists to estimate the risk
of colonisation and destabilisation of large algae monocultures.
Given the high rate of destruction of cultures grown in
"micro-ponds", it is not unreasonable to assume that this rate
increases as a function of the size of the ponds. As yet, there are
not enough datasets to look for a correlation between pond-size and
the risk of culture-loss. But one thing is certain: the ultra-large
scale production schemes ("replacing all U.S. diesel demand with
algae grown in one big pond facility located in the Sonoran desert")
that have been proposed are faced with this important lack of
knowledge on phytopathological risks involved in large scale
algae-culture.
-risk of species contamination and the uncontrolled spread of
genetically modified algae:
from the ASP we learn that mass algae production is not likely to be
feasible unless genetically modified algae are engineered which are
stable, contain a high amount of lipids and can be harvested easily.
The problem with such a development would obviously be contamination
of water bodies not destined for biofuel prodution. The genetically
altered algae species would be so strong, that they would easily
destroy species that thrive naturally in water bodies. The existing
algae colonies in natural water bodies are often caught in a fragile
balance, with 'predators' fighting each other, limiting the overall
colonisation of the water body. A genetically altered species could
unsettle this balance and cause a major pest problem.
The same can of course be said of genetically altered energy crops.
But it is clear that biomass yields of tropical crops are high enough
to maintain a positive energy balance; in theory, no genetically
modified crops are needed to produce satisfactory amounts of biomass.
-harvesting problems:
modern tropical agriculture (let us take the sugarcane industry as an
example) is highly mechanised when it comes to harvesting and
processing biomass. Harvesting techniques for algae have not attained
the same level of perfection. The tried technologies (membranes,
bioflocculation) are a limiting factor when it comes to choosing the
best algae; some interesting micro-organisms are physically too small
to be practically harvesteable by membranes; whereas the flocculation
technique does not yield consistent results with all species.
Moreover, flocculants are very expensive and some species need a high
amount of them in order to flocculate.
-opportunity costs, system flexibility and crop portfolios
A major disadvantage of algae production systems is that once the
investments in the technologies have been made, they must be used,
even when the economics change radically. This is not the case in
terrestrial agriculture (at least not when it involves annual crops),
where farmers can switch between crops and markets, and choose to
grow crops that promise to make most profits depending on market
predictions. In terrestrial agriculture assets (like land and
machinery) can be used for a wide variety of crops and products. This
allows for flexibility and for adapting choices to market
opportunities.
Energy farmers can produce feedstocks for biofuels one year, and
decide to grow food crops the next. This would be hard to achieve
with algae production systems, which have to be finetuned and
designed to accomodate a specific range of species, catering to a
very specific market. The volatility of oil prices influences the
volatility of bioenergy markets and is now ultimately influencing the
market for food products. Terrestrial farmers can switch between the
two. Algae-culturalists can not, which entails a definite risk.
All in all, algae-culture does not have to be seen as a strict
competitor with energy crops. Algae ponds can be located in arid
regions not suitable for agriculture (such as deserts). The only
problem is their high production costs (on an energy equivalent
basis) and the lack of flexibility of the production system, compared
to those of (tropical) terrestrial energy crops.
Algae for biohydrogen and biogas production
The ASP focused on the production of biodiesel from algae. However,
the micro-organisms have been studied as potential feedstocks for the
production of gaseious fuels such as hydrogen and biogas
(biomethane). In the 1950s and 1970s, several field trials aimed at
obtaining biogas were carried out (mentioned in the document we are
referring to here) with encouraging results.
"The idea of producing methane gas from algae was proposed in the
early 1950s. These early researchers visualized a process in which
wastewater could be used as a medium and source of nutrients for
algae production. The concept found a new life with the energy crisis
of the 1970s. DOE and its predecessors funded work on this combined
process for wastewater treatment and energy production during the
1970s. This approach had the benefit of serving multiple needs-both
environmental and energy-related. It was seen as a way of introducing
this alternative energy source in a near-term timeframe." [3]
Algae were grown on the sludge of waste water management facilities,
in open ponds, after which their biomass was harvested and used as a
substrate in a biogas digester. It was shown that many species make
for a good subtrate for anaerobic fermentation:
"The concept of microalgae biomass production for conversion to fuels
(biogas) was first suggested in the early 1950s. Shortly thereafter,
Golueke and coworkers at the University of California-Berkeley
demonstrated, at the laboratory scale, the concept of using
microalgae as a substrate for anaerobic digestion, and the reuse of
the digester effluent as a source of nutrients.
Oswald and Golueke presented a conceptual analysis of this process,
in which large (40-ha) ponds would be used to grow microalgae. The
algae would be digested to methane gas used to produce electricity.
The residues of the digestions and the flue gas from the power plant
would be recycled to the ponds to grow additional batches of algal
biomass. Wastewaters would provide makeup water and nutrients. The
authors predicted that microalgae biomass production of electricity
could be cost-competitive with nuclear energy. This concept was
revived in the early 1970s with the start of the energy crisis. The
National Science Foundation-Research Applied to National Needs
Program (NSF-RANN) supported a laboratory study of microalgae
fermentations to methane gas (Uziel et al.1975). Using both fresh and
dried biomass of six algal species, roughly 60% of algal biomass
energy content converted to methane gas." [145]
However, the researchers found that the organically rich sludge on
which the algae were fed, yielded more methane than the algae that
had grown on it. So the entire venture was seen as inefficient: why
make the detour of converting a prime biogas substrate that yields
reasonable quantities of methane, into a substrate that yields less?
Even though it would take us too far to delve into the potential of
hydrogen producing algae, some past and more recent developments are
worth noting. The oil crisis in 1973 already prompted research on
biological hydrogen production, including photosynthetic production,
as part of the search for alternative energy technologies. Green
algae were known as light-dependent, water-splitting catalysts, but
the characteristics of their hydrogen production were not practical
for exploitation.
Hydrogenase is too oxygen-labile for sustainable hydrogen production:
light-dependent hydrogen production ceases within a few to several
tens of minutes since photosynthetically produced oxygen inhibits or
inactivates hydrogenases. A continuous gas flow system designed to
maintain low oxygen concentrations within the reaction vessel, was
employed in basic studies, but has not been found practically
applicable.
Scientists later found that a particular species of algae,
Scenedesmus, does produce molecular hydrogen under light conditions
after being kept under anaerobic and dark conditions.
Basic studies on the mechanisms involved in hydrogen production
determined that the reducing power (electron donation) of hydrogenase
does not always come from water, but may sometimes originate
intracellularly from organic compounds such as starch. The
contribution of the decomposition of organic compounds to hydrogen
production is dependent on the algal species concerned, and on
culture conditions. Even when organic compounds are involved in
hydrogen production, an electron source can be derived from water,
since organic compounds are synthesized by oxygenic photosynthesis.
The reason for hydrogenase inactivity in green algae under normal
photosynthetic growth conditions is unclear. Hydrogenase is thought
to become active in order to excrete excess reducing power under
specific conditions, such as anaerobic conditions.
Very high (10 to 20%) efficiencies of light conversion to hydrogen
have been reported, based on PAR (photosynthetically active radiation
which includes light energy of 400-700nm in wavelength). Recent
findings show that a kind of "short circuit" of photosynthesis
exists, whereby hydrogen production and CO2 fixation occur by a
single photosystem (photosystem II only) of another species, a
Chlamydomonas mutant.
Green algae are applicable in another method of hydrogen production.
Scenedesmus produces hydrogen gas not only under light conditions,
but also fermentatively under dark anaerobic conditions, with
intracellular starch as a reducing source. Although the rate of
fermentative hydrogen production per unit of dry cell weight, was
less than that obtained through light-dependent hydrogen production,
hydrogen production was sustainable due to the absence of oxygen. On
the basis of experiments conducted on fermentative hydrogen
production under dark conditions, other scientists have proposed
hydrogen production in a light/dark cycle. According to their
proposal, CO2 is reduced to starch by photosynthesis in the daytime
(under light conditions) and the starch thus formed, is decomposed to
hydrogen gas and organic acids and/or alcohols under anaerobic
conditions during nighttime (under dark conditions).
The technological merits of this proposal include the fact that
oxygen-inactivation of hydrogenase can be prevented through
maintenance of green algae under anaerobic conditions, nighttime
hours are used effectively, temporal separation of hydrogen and
oxygen production does not require gas separation for simultaneous
water-splitting, and organic acids and alcohols can be converted to
hydrogen gas by photosynthetic bacteria under light conditions. A
pilot plant using a combined system of green algae and photosynthetic
bacteria was operated within a power plant of Kansai Electric Power
Co. Ltd. (Nankoh, Osaka, Japan). Researchers at this plant recently
proposed chemical digestion of algal biomass as a means of producing
substrates for photosynthetic bacteria, thus improving the yield of
starch degradation.
Finally, cyanobacteria have also been found to produce hydrogen gas
auto-fermentatively under dark and anaerobic conditions. Spirulina
species were demonstrated to have the highest activity among
cyanobacteria tested. The nature of the electron carrier for
hydrogenase in cyanobacteria is still unclear.
All in all, hydrogenases have been purified and partially
characterized in only a few cyanobacteria and microalgae.
The question remains: will these laboratory experiments ever make it
on a large scale? Most of the trials require closed photobioreactors
(in order to arrive at anaerobic conditions) and we already know that
these reactors are a major barrier to cost-effective biofuel
production from algae. Finally, no hard data are available on the
overall productivity of hydrogen-producing algae. If they convert
starches into hydrogen very efficiently, this doesn't mean that their
overall gross starch productivity and consequent gross hydrogen
productivity is equally impressive. The latter point is crucial,
because these algae systems compete with ordinary terrestrial energy
crop production, the biomass of which can already be converted into
both liquid fuels and gaseous fuels, quite efficiently (either
thermochemically, through gasification and pyrolysis, or
biochemically, through the enzymatic breakdown of lignocellulose).
Conclusions
One recurring conclusion of all the studies is that harvestable algae
biomass yields max out at around 50 tonnes per hectare per year. This
is below the biomass yields of most tropical energy crops. In most
field situations, algae also tend to be unstable, which entails the
risk of entire cultures being destroyed by invasive competitors.
Harvesting algae is not an easy task; tried cost-effective and
efficient techniques limit the number of species that can be used for
large-scale biofuel production and limit the biomass productivity of
the potentially interesting candidates somewhat. Finally, the ASP did
not succeed in developing a 'super' algae that shows all the desired
properties that make continuous biofuel production on a large scale
feasible.
Given the fact that at the height of the oil crisis (1979-1980), when
oil prices topped records that still stand today, photobioreactors
were deemed to be both impractical and too costly, we think that the
situation today is not much different. The ASP radically chose the
'open pond' option from the beginning, and if algae biofuels are ever
to succeed, this production system will most likely be the one that
is used.
Finally, the claims that algae yield 'enormous' amounts of useable
biomass, have never been demonstrated or substantiated. Algae
production in photobioreactors has never left the laboratory or pilot
phase and no energy balance and greenhouse gas balance analyses exist
for biofuels obtained from such system. The only real data we can
rely on, so far, are those of the projects carried out under the
Aquatic Species Program.
More information:
National Renewable Energy Laboratory: A Look Back at the Department
of Energy's Aquatic Species Program: Biodiesel Production from Algae
[*.pdf], close-out report, 1998.
Michael Briggs, University of New Hampshire, Physics Department,
Widescale Biodiesel Production from Algae, 2004.
BBC Journal h2g2: "Biohydrogen" -may 31, 2004.
Biopact: Biofuels from algae - new breakthrough claimed, July 22, 2006.
Biopact: Growing algae for biofuels in the Negev desert, August 17, 2006.
Biopact: Biohydrogen, a way to revive the 'hydrogen economy'?, August 20, 2006.
posted by Biopact team at 12:06 AM
2 Comments:
JPatten said...
This is a well considered if long analysis of oil production from
algae pointing to some of the failures in the past. However I don't
share the overall theme of pessimism because the studies referred to
ended at least ten years ago and in the interim technology has
continued to evolve and will continue to do so. With regard to
bio-reactors a number of clever but incremental ideas gradually
coming together could change things for the better. For instance
using magnets to alter the properties of calcium in water has long
been used by Koi pond owners to suppress blanket weed in their fish
ponds. Could a similar technique be used to stop algae attaching to
light sources in bio-reactors? Many have referred to locating
bio-reactors beside power stations in order to recycle CO2 but seem
to have missed an important additional bonus which could further
enhance matters and this is the availability of unused waste heat.
Not all power stations sited in urban areas (and elsewhere) are
suitable for hooking up to metropolitan heating schemes and there is
plenty of waste heat out there waiting to be used. Additionally could
some of this waste heat be used in some way to agitate the water
borne algae in the bio-reactors as well as providing a heat source to
encourage growth? I think if we push hard enough and if we are
imaginative enough many of the current problems to do with
bio-reactors could be solved. The worst thing would be to close our
minds from the start. Alternative energy has been continually plagued
with overly vocal nay sayers most particularly those who can see
nothing other than the oil economy. Interestingly pond production of
algae could be a fantastic development for many parts of Africa given
the availability of sunshine so I would therefore urge Biopact to
take it all just a little bit more seriously.
12:32 PM
Biopact team said...
Hi jpatten, thanks for your insights and suggestions.
The main reason why we wrote the piece is to temper some of the
unfounded and unsubstantiated enthusiasm surrounding algae. We try to
keep a critical eye on all biofuel initiatives and developments. One
of the most important aspects of such an attitude is to remain
sceptical about claims in press releases.
First and further-generation biofuels based on terrestrial crops
receive questions on energy balances and lifecycle efficiencies on a
daily basis. Why shouldn't algae biofuels?
You may have read in our previous pieces on algae biofuels that we
are in favor of the technology, provided it makes sense from an
energy efficiency point of view. If it works, then all the better for
all of us. But if it doesn't, we should devote our time and money to
technologies that make more sense.
When it comes to algae-culture in Africa: there has been a small open
pond experiment in Mozambique, carried out by a Dutch students. We
are awaiting the results of this project.
One thing is certain: we have never read a critical assessment of
algae biofuels. We wrote one, sticking to the facts (on biomass
yields), and some may not like these facts.
We have decided no longer to mimick the uncritical press releases on
algae and no longer to report on developments in this sector, as long
as no basic lifecycle assessments are made available.
ends
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