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Why Algal Biofuels May Never Hold the Key to the Future

By Professor Chris Rhodes | Sun, 19 February 2012 17:59 | 14

The depletion of world rock phosphate reserves will restrict the amount of food that can be grown, a situation that can only be compounded by the production of biofuels, including the potential large-scale generation of diesel from algae. The world population has risen to its present number of 7 billion in consequence of cheap fertilizers, pesticides and energy sources, particularly oil. Almost all modern farming has been engineered to depend on phosphate fertilizers, and those made from natural gas, e.g. ammonium nitrate, and on oil to run tractors etc. and to distribute the final produce. A peak in worldwide production of rock phosphate is expected by 2030, which lends fears over how much food the world will be able to grow in the future, against a rising number of mouths to feed [1]. Consensus of analytical opinion is that we are close to the peak in world oil production too.

One proposed solution to the latter problem is to substitute oil-based fuels by biofuels, although this is not as straightforward as is often presented. In addition to the simple fact that growing fuel-crops must inevitably compete for limited arable land on which to grow food-crops, there are vital differences in the properties of biofuels, e.g. biodiesel and bioethanol, from conventional hydrocarbon fuels such as petrol and diesel, which will necessitate the adaptation of engine-designs to use them, for example in regard to viscosity at low temperatures, e.g. in planes flying in the frigidity of the troposphere. Raw ethanol needs to be burned in a specially adapted engine to recover more of its energy in terms of tank to wheels miles, otherwise it could deliver only about 70% of the "kick" of petrol, pound for pound.

In order to obviate the competition between fuel and food crops, it has been proposed to grow algae to make biodiesel from. Some strains of algae can produce 50% of their weight of oil, which is transesterified into biodiesel in the same way that plant oils are. Compared to e.g. rapeseed which might yield a tonne of biodiesel per hectare, or 8 tonnes from palm-oil, perhaps 40 - 90 tonnes per hectare is thought possible from algae [2], grown in ponds of equivalent area. Since the ponds can in principle be placed anywhere, there is no need to use arable land for them. Some algae grow well on salt-water too which avoids diverting increasingly precious freshwater from normal uses, as is the case for growing crops which require enormous quantities of freshwater.

The algae route sounds almost too good to be true. Having set-up these ponds, albeit on a large scale, i.e. they would need an area of 10,000 km^2 (at 40 t/ha) to produce 40 million tonnes of diesel, which is enough to match the UK's transportation demand for fuel if all vehicles were run on diesel-engines [the latter are more efficient in terms of tank to wheels miles by about 40% than petrol-fuelled spark-ignition engines], one could ideally have them to absorb CO2 from smokestacks (thus simultaneously solving another little problem) by photosynthesis, driven only by the flux of natural sunlight. The premise is basically true; however, for algae to grow, vital nutrients are also required, as a simple elemental analysis of dried algae will confirm. Phosphorus, though present in under 1% of that total mass, is one such vital ingredient, without which algal growth is negligible. I have used two different methods of calculation to estimate how much phosphate would be needed to grow enough algae, first to fuel the UK and then to fuel the world:

(1) I have taken as illustrative the analysis of dried Chlorella [2], which contains 895 mg of elemental phosphorus per 100 g of algae.

UK Case: To make 40 million tonnes of diesel would require 80 million tonnes of algae (assuming that 50% of it is oil and this can be converted 100% to diesel).
The amount of "phosphate" in the algae is 0.895 x (95/31) = 2.74 %. (MW PO4(3-) is 95, that of P = 31).

Hence that much algae would contain: 80 million x 0.0274 = 2.19 million tonnes of phosphate. Taking the chemical composition of the mineral as fluorapatite, Ca5(PO4)3F, MW 504, we can say that this amount of "phosphate" is contained in 3.87 million tonnes of rock phosphate.

World Case: The world gets through 30 billion barrels of oil a year, of which 70% is used for transportation (assumed). Since 1 tonne of oil is contained in 7.3 barrels, this equals 30 x 10^9/7.3 = 4.1 x 10^9 tonnes and 70% of that = 2.88 x 10^9 tonnes of oil for transportation.

So this would need twice that mass of algae = 5.76 x 10^9 tonnes of it, containing:
5.76 x 10^9 x 0.0274 = 158 million tonnes of phosphate. As before, taking the chemical composition of phosphate as fluorapatite, Ca5(PO4)3F, MW 504, this amount of "phosphate" is contained in 279 million tonnes of rock phosphate.

(2) To provide an independent estimate of these figures, I note that growth of this algae is efficient in a medium containing a concentration of 0.03 - 0.06% phosphorus; since I am not trying to be alarmist, I shall use the lower part of the range, i.e 0.03% P. "Ponds" for growing algae vary in depth from 0.3 - 1.5 m, but I shall assume a depth of 0.3 m.

UK Case: assuming (vide supra) that producing 40 million tonnes of oil (assumed equal to the final amount of diesel, to simplify the illustration) would need a pond/tank area of 10,000 km^2. 10,000 km^2 = 1,000,000 ha and at a depth of 0.3 m, this amounts to a volume of: 1,000,000 x (1 x 10^4 m^2/ha) x 0.3 m = 3 x 10^9 m^3.

A concentration of 0.03 % P = 0.092% phosphate, and so each m^3 (1 m^3 weighs 1 tonne) of volume contains 0.092/100 = 9.2 x 10^-4 tonnes (920 grams) of phosphate. Therefore, we need:

3 x 10^9 x 9.2 x 10^-4 = 2.76 million tonnes of phosphate, which is in reasonable accord with the amount of phosphate taken-up by the algae (2.19 million tonnes), as deduced above. This corresponds to 4.87 million tonnes of rock phosphate.


World Case: The whole world needs 2.88 x 10^9 tonnes of oil, which would take an area of 2.88 x 10^9/40 t/ha = 7.20 x 10^7 ha of land to produce it.

7.2 x 10^7 ha x (10^4 m^2/ha) = 7.2 x 10^11 m^2 and at a pond depth of 0.3 m they would occupy a volume = 2.16 x 10^11 m^3. Assuming a density of 1 tonne = 1 m^3, and a concentration of PO4(3-) = 0.092%, we need:

2.16 x 10^11 x 0.092/100 = 1.99 x 10^8 tonnes of phosphate, i.e. 199 million tonnes. This corresponds to 352 million tonnes of rock phosphate.

This is also in reasonable accord with the figure deduced from the mass of algae accepting that not all of the P would be withdrawn from solution during the algal growth.


Now, world rock phosphate production amounts to around 140 million tonnes (noting that we need 352 million tonnes to grow all the algae), and food production is already being thought compromised by phosphate resource depletion. The US produces less than 40 million tonnes of rock phosphate annually, but would require enough to produce around 25% of the world's total algal diesel, in accord with its current "share" of world petroleum-based fuel, or 88 million tonnes of phosphate. Hence, for the US, security of fuel supply could not be met by algae-to-diesel production using even all its indigenous rock phosphate output, and significant imports of the mineral are still needed. This is in addition to the amount of the mineral needed for agriculture.

The world total of rock phosphate is reckoned at 8,000 million tonnes and that in the US at 2,850 million tonnes (by a Hubbert Linearization analysis). However, as is true of all resources, what matters is the rate at which they can be produced.

I remain optimistic over algal diesel, but clearly if it is to be implemented on a serious scale its phosphorus has to come from elsewhere than mineral rock phosphate. There are regions of the sea that are relatively high in phosphates and could in principle be concentrated to the desired amount to grow algae, especially as salinity is not necessarily a problem. Recycling phosphorus from manure and other kinds of plant and animal waste appears to be the only means to maintain agriculture at its present level, and certainly if its activities will be increased to include growing algae. In principle too, the phosphorus content of the algal-waste left after the oil-extraction process could be recycled into growing the next batch of algae. These are all likely to be energy-intensive processes, however, requiring "fuel" of some kind, in their own right. A recent study [4] concluded that growing algae could become cost-effective if it is combined with environmental clean-up strategies, namely sewage wastewater treatment and reducing CO2 emissions from smokestacks of fossil-fuelled power stations or cement factories. This combination appears very attractive, since the impacts of releasing nitrogen and phosphorus into the environment and also those of greenhouse gases might be mitigated, while conserving precious N/P nutrient and simultaneously producing a material that can replace crude oil as a fuel feedstock.

It is salutary that there remains a competition between growing crops (algae) for fuel and those for food, even if not directly in terms of land, for the fertilizers that both depend upon. This illustrates for me the complex and interconnected nature of, indeed Nature, and that like any stressed chain, will ultimately converge its forces onto the weakest link in the "it takes energy to extract energy" sequence.

The is a Hubbert-type analysis of human population growth indicates that rather than rising to the putative "9 billion by 2050" scenario, it will instead peak around the year 2025 at 7.3 billion, and then fall [5]. It is probably significant too that that population growth curve fits very closely both with that for world phosphate production and another for world oil production [5]. It seems to me highly indicative that it is the decline in resources that will underpin our demise in numbers as is true of any species: from a colony of human beings growing on the Earth, to a colony of bacteria growing on agar nutrient in a Petri-dish.

By. Professor Chris Rhodes

Professor Chris Rhodes is a writer and researcher. He studied chemistry at Sussex University, earning both a B.Sc and a Doctoral degree (D.Phil.); rising to become the youngest professor of physical chemistry in the U.K. at the age of 34.
A prolific author, Chris has published more than 400 research and popular science articles (some in national newspapers: The Independent and The Daily Telegraph)
He has recently published his first novel, "University Shambles" was published in April 2009 (Melrose Books). http://universityshambles.com

About the author

More recent articles by Professor Chris Rhodes

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Tue 19 February 2013
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Sun 10 February 2013
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Sun 27 January 2013
Why EROEI Means Mining in Space will Never Work
Thu 24 January 2013
Low Energy Light Bulbs Not So "Green" After All?

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  • Keith on February 20 2012 said:
    I find the calculation for phosphate % a bit upside down. P+Ox4 is indeed 95 and P is 31 but the percent P in PO4 is 31/95. If there are 895 mg PO4 in 100 gm then there are 895*31/95 mg of P and 895*16*4/95 mg of Oxygen bound phosphate. It's still a large task to feed and heat 7 billion people. One has to shudder to think that peak oil also has a corollary to people as well. I always favored nuclear energy as a means to extend prosperity while we solve our population problems but there are not any easy answers.
  • fatalgae on February 20 2012 said:
    ARPA-E halts algae project, citing missed milestones
    Jim Lane | February 16, 2012

    Share"In Washington, the DOE has halted a research project at Iowa State University funded by ARPA-E to develop biofuel feedstock from an aquatic micro-organism for failing to reach research milestones. About 56% of the $4.4 million grant was used. Politicians against increasing APRA-E funding as proposed by President Obama’s new budget are using it and other halted ARPA-E projects as examples to reject the program."

    Know doubt why the DOE BIOMASS PROGRAM AND ALGAE RESEARCHERS ARE BEING INVESTIGATED!

    Solydra story is opening a huge can of worms at the DOE LOAN GURANTEE LOAN PROGRAM. Its not just about the Solar loan guarantee program. Look at all the millions in fees collected by the DOE LOAN GUARANTEE PROGRAM with algae projects less than 20% completed.

    An audit is being done on all DOE GRANTS to algae researchers and individuals from the DOE that are now working in private industry. Very incestuous!

    The US taxpayer has spent over $2.5 billion dollars over the last 50 years on algae research. To date, nothing has been commercialized by any algae researcher at any university.

    The REAL question is: Does the DOE BIOMASS PROGRAM really want the US off of foreign oil or do they want to continue funding more grants for algae research to keep algae researchers employed at universities for another 50 years?

    In business, you are not given 50 years to research anything. The problem is in the Congressional Mandate that says the DOE can only use taxpayer monies on algae research, NOT algae production in the US. So far, algae research has not got the US off of foreign oil for the last 50 years!

    A Concerned Taxpayer
  • art on February 20 2012 said:
    Dear Sir,

    thank you for the analysis regarding algae and phosphate. two remarks;

    the good thing about algae that they are the only microbes that can capture P from dilute phospate solutions powered by solar input, they are extremely efficient scavengers for phosphate due to their high affinity PO4 uptake mechanisms.

    The second is that algae display luxury PO4 uptake and store them as polyphosphates. P content in algae can vary between 0.3 % to 5 %....

    the big advantage of algae over current landbased agricultural practices is that the process of growing algae seems better suited for optimized use op P
  • Durwood M. Dugger on February 20 2012 said:
    As Dr. Rhodes has been a proponent of biofuels - particularly algae biofuels, I applaud Dr. Rhodes examination of the peak phosphate problem's impact on both our expectations for biofuel energy production and its competition with food production. However, I think if anything - he too cautiously understates the reasons for concern.

    Global and US rock phosphate production demonstrably peaked in the late 80s. Whether global phosphate production may be on a peak - or a peak plateau - is from a peak food and peak population standpoint - only academic. There is a growing awareness in the scientific community that peak oil is a minor problem compared to peak phosphate. Governments, politicians and the petrochemical/fertilizer industry would rather side step this complicated issue - it's the human population at large which is at risk of the damage that their negligence incurs. Unfortunately, the human population at large does not understand that phosphorus is the single most limiting factor of any biological population's size within a given ecosystem.

    Thinking that we have an accurate estimate of the amount of useable phosphates seems to be our first mistake. The following article provide a a very excellent analysis and graphic portrayal of global phosphate productions peak and progression toward depletion: (http://www.energybulletin.net/node/33164)

    "Although many estimates for when peak phosphorus will occur have been made, many of them are marred by inaccurate knowledge of the quantity of world phosphate reserves. This is largely in part due to distrust in phosphate mines reports of total reserves, with the expectation that these values will be inflated to protect their business interests. The USGS, which obtains its figures from foreign governments, estimates that phosphorus reserves worldwide are 65 billion tons of which 15 billion tons is mineable, while world mining production in 2010 was 176 million tons.[5] (Reserve figures refer to the amount in deposits recoverable at current market prices with present technology; phosphorus comprises 0.1% by mass[6] of the Earth's 3 * 1019 ton crust,[7] quadrillions of tons in total but at predominantly lower concentration than the most inexpensive deposits). These reserve figures, although widely used for predicting future peak phosphorus, have raised concern as to their accuracy due to the fact that they aren't independently verified by the USGS.[8] The depletion of phosphorus is more relevant to our world today than the depletion of oil is. Phosphorus is a major component in fertilizer, without which fertilizer will be rendered useless. Without fertilizer, two thirds of the worlds population will starve because the Earth cannot support our demands for food.[9" (http://en.wikipedia.org/wiki/Peak_phosphorus)

    "Phosphate deposits can contain significant amounts of naturally occurring heavy metals. Mining operations processing phosphate rock can leave tailings piles containing elevated levels of cadmium, lead, nickel, copper, chromium, and uranium. Unless carefully managed, these waste products can leach heavy metals into groundwater or nearby estuaries. Uptake of these substances by plants and marine life can lead to concentration of toxic heavy metals in food products.[8]"
    "Some phosphate rock deposits are notable for their inclusion of significant quantities of radioactive uranium isotopes. This syndrome is noteworthy because radioactivity can be released into surface waters[6] in the process of application of the resultant phosphate fertilizer (e.g. in many tobacco farming operations in the southeast USA)." (http://en.wikipedia.org/wiki/Phosphate)

    Dr. Rhodes doesn't adequately emphasize the con fluency between the economics of peak oil and peak phosphate. Essentially, as the price of oil goes up so do the production costs of mined rock phosphates - since most of phosphate mining costs are energy. As the price of mined rocked phosphate production goes up - the amounts of global rock phosphates that can be mined at those concentrations (economically feasible to mine) - go down. - resulting in much smaller economically viable phosphate reserves than currently being anticipated. Whether phosphates come from land based mines or as Dr. Rhodes suggests might come from mining the oceans - it's their impact on food production economics, population dynamics, and global political stability that need to be far more carefully examined.

    Recycling phosphorus from wastes only slows our time to when our population must rely on the natural phosphorus replenishment cycle that previously (up to the industrial revolution of mid-1800s) demonstrated a maximum sustainable limit of 2 billion humans or less. We will survive peak oil with use of solar, wind, tide and other alternative energies - without the need for more phosphate dependent biofuel production. Peak phosphate is something we are going to have to deal with sooner than later - if we develop a global biofuel industry.
  • Dr. Aaron Wolf Baum of AlgaeLab.org on February 20 2012 said:
    In a P-limited future world, microalgae are by far the best crop to grow, for 2 main reasons:

    1. They are the most effective organism at scavenging dilute P from water, capable of absorbing 90+% from a culture into their biomass. This also means they are good at cleaning up fertilizer-contaminated ground water, as well as waste water; not only doe this address peak P, it also deals with the much more pressing issue of eutrophication (i.e. "dead zones).

    2. Since algae cultures are well contained, compared to conventional crops, P loss can be practically eliminated, and P in spent biomass can be returned to the culture after the desired products have been extracted.

    For these reasons I would say that peak P is in fact a selling point for large-scale algae production.

    Respectfully,
    Dr. Aaron Wolf Baum of AlgaeLab.org
  • Durwood M. Dugger on February 21 2012 said:
    It's easy to confuse the qualities, advantages and scalability of open water algae macrophage culture where the algae truly do derive their phosphorus from over-nutrified coastal waters (but only economically successfully for a relatively small scale high value specialty food and nutraceutical production) - with algal biofuel production in open pond systems and photo bioreactors (PBRs) which have to have phosphorous and other chemical fertilizers and trace elements added for large scale commercial scale production. While it's technically possible to recycle phosphorus with algae - it is far from economically feasible. For biofuels neither open ocean macrophyte production, open pond, nor PBR production of algal biofuels have achieved commercial feasibility even after some 80 years of research (as another reader laments). For algae to impact our future energy needs it not only needs to be an efficient phosphorus user, but it needs to compete with the production costs of other alternative and fossil energy sources. Otherwise, algae biofuel's dramatically higher production cost and it's competition with food crops will also dramatically alter our current life styles where we spend comparatively little of our work effort/income on either energy or food to maintain our current life style.

    Regardless of algae's more efficient uptake of phosphorus - economically viable commercial production of algae biofuels either in open ponds or photo-bio-reactors have been shown to be unsustainable because of their dependence on chemical fertilizers in mass balance analysis studies by the U. of Kansas, MIT, Rand Corp, NREL and the Innovation Counsel of B.C and other research organizations.

    It would seem to be an extremely poor strategy to commit to large scale biofuel production - unless we can first effectively solve (not theoretical solutions) our peak phosphorus problem and it's limitations on human food productions. Turning peak phosphorous that is so essential to current food production technology to important, but far less essential energy production - which we already are making progress at substituting with solar and wind - would be extremely unwise and risky.
  • Tom on February 21 2012 said:
    Much of oil's spike is speculative and detached from fundamentals. Eventually the fundamentals would hold true and so the speculators serve a useful purpose even if they are just in it for the $$$.

    I agree with the fertilizer question but I think we could get many of these nutrients from sewage and waste water. Algae could possibly serve 2 purposes (the one you mention) and also to help clean waste water effectively and still getting the nutrients it needs. All of the worlds oil came from ancient algae deposits. Just baked over millions of years at high heat, it doesn't break down in the cold like algae oil would. Perhaps science will solve that as well.
  • Anna Sternfeldt on February 22 2012 said:
    Yes, to use sewage and waste water is a good idea. But what strikes me on this peak matter is that with time even sewage and waste water may be scarce and depleted (it can't come out more than we consume). It is a bit scary...especially for our children. We are really pushing the entropy law. It will likely be as said, that the scarce resources will reduce our numbers, instead of us adjusting to the amount of resources..unfortunately...
    Anna

    "Don't blow it - good planets are hard to find."
    www.best-alternative-fuel-sources.com
  • Chris Rhodes on February 22 2012 said:
    Keith: There are 895 mg of "elemental phosphorus" (NOT phosphate) in the algae. So, there are 95/31 x 895 mg of "phosphate" = 2,743 mg of it. Expressed as a percentage that is 2.74%, exactly as I have it. OK? I concur with you entirely that peak oil is but one aspect of the resource crisis and since phosphate is mined using machinery that runs on oil-derived fuels, there is a direct connection between the two.

    To Mr Dugger: I am indeed enthusiastic about the prospects of algae as a fuel source, but I am dismayed at the aspect of competition if not for land, but phosphate, between "crops" for food and crops for fuel. What I now realise is that we have a huge problem of feeding 7 billion people (and animals) by means of industrialized agriculture, which depends on phosphate, nitrogen (from the Haber Bosch process), freshwater and oil for fertilizers.

    I put this to a colleague of mine at Transition Town Reading, who is educating me on the finer points of permaculture, as he says that this style of agriculture could help the situation since (1) soil fungi can help mobilize phosphate in the soil, and (2) that building mulch in the soil helps to reduce the loss of phosphate through run-off. The problem is that such methods struggle to meet the yields that are attained through industrial farming.

    In regard to the other comments, I agree that we should not give-up on algae yet. Certainly we will need to use resources more efficiently, and getting back P and N from sewage etc. is the way forward. It has been suggested that algae might be used to extract P from sea-current where the concentration is low but reasonable.

    As to the timing of peak-oil, there are various estimates. That accepted, even if we had 50 years until it's arrival, it would make sense to address the problem now.

    Regards,

    Chris Rhodes
  • Larry Pierson on February 24 2012 said:
    The author overlooked something so simple, I'm stunned he missed it. All the trace minerals in algal fuel can be extracted and recycled. And they exist in suspension in the sea, where they can also be extracted if the prince of biofuels is high enough to justify the cost of doing so.

    Bottom line is, algal fuels will not indefinitely consume a limited resource, it will only a year or so's supply to jump start production, after which very little more will be required to maintain the process.
  • Durwood M. Dugger on February 24 2012 said:
    Hi Chris,

    I couldn't agree more about your final comment on the urgency of a new technical paradigm in phosphate production technology. However, you should be aware that people have been working on this problem since WW II and while it's certainly technically possible - the economics are not comparable to existing technologies.

    If you search long enough on Google it seems someone has already answered the question for which you were putting all the data together. Regarding the affects of algae and other biofuels on peak phosphate - I found this very interesting and recommend it very highly:

    http://seekingalpha.com/article/182522-taking-stock-of-phosphorus-and-biofuels

    There seems to be more than enough support therein to make us very cautious about developing a major biofuel industry until we have peak oil/alternative energy and a new technology for phosphate production well in place. Otherwise like cows, we'll spending our days trying to find enough to eat to survive to the next day.

    All the best,

    Durwood M. Dugger, Pres.
    www.biocepts.com
  • Chris Rhodes on April 05 2012 said:
    Dear Larry,

    I have indeed NOT overlooked the aspect of phosphorus recycling, since I clearly state: "In principle too, the phosphorus content of the algal-waste left after the oil-extraction process could be recycled into growing the next batch of algae. These are all likely to be energy-intensive processes, however, requiring "fuel" of some kind, in their own right."

    How exactly the extraction of phosphate from the algal waste might be done remains to be determined.

    My point clearly is that a truly vast amount of phosphate needs to be garnered to be pout in circulation in the first place.

    Regards,

    Chris
  • Sean on October 22 2012 said:
    dear chris and larry.
    once you have squeezed all the oils you are looking for out, put the waste seaweed/algae into a digester, pull methane out, use the resultant sludge, which has all the minerals in it, either to fertilise land crops, or dump back into the growing pond and grow more seaweed/algae.

    the methane produced will not be in huge quantities, but the aerobic digestion should enable the uptake of minerals once they are used to fertilise crops of either land or sea .

    as far as the "huge economic costs" I don't think anyone will get too put out by a big black plastic bag. (you could make a gobar gas style digester if you wanted) the economic cost will simply be finding land to put it on.
  • Don Schroder on October 24 2013 said:
    The article doesnt take into account the abundance of phosphates and other trace minerals and nutrients in waste water. Especially in a closed system where spent biomass is converted back to phosphates and nitrates naturally. Rock phosphate is for centralized production. Where as the accessibility of a decentralized network of mid to small scale closed loop systems, deployed to scale, at the point of use, is the prime advantage of algae cultivation.

    Entrepreneurs that ignore the advantages of accessible, mobile, domestic, automatic, and multifunctional biomass production, provided solely by microbes alone, are dooming themselves to failure.

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