Sunday, April 06, 2008

Could Peak Phosphate be Algal Diesel's Achilles' Heel?

The depletion of world phosphate reserves will impact on the production of biofuels, including the potential wide-scale generation of diesel from algae. The world population has risen to its present number of 6.7 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. Worldwide production of phosphate has now peaked (in the US the peak came in the late 1980's), which lends fears as to 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 from which to make biodiesel. 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. soy which might yield a tonne of diesel per hectare, or 8 tonnes from palm-oil, in excess of 100 tonnes (I shall assume 125 tonnes) per hectare is thought possible from algae, 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 3,200 km^2 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 leave them to absorb CO2 from the atmosphere (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.

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.

(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 around 0.6 - 1.5 metres and so I shall assume a depth of 1 m for simplicity.

UK Case: I worked-out previously [3] 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 3,200 km^2. 3,200 km^2 = 320,000 ha and at a depth of 1m, this amounts to a volume of: 320,000 x (1 x 10^4 m^2/ha) x 1m = 3.2 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:

3.2 x 10^9 x 9.2 x 10^-4 = 2.94 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.

World Case: The whole world needs 2.88 x 10^9 tonnes of oil, which would take an area of 2.88 x 10^9/125 t/ha = 2.30 x 10^7 ha of land to produce it.

2.3 x 10^7 ha x (10^4 m^2/ha) = 2.3 x 10^11 m^2 and at a pond depth of 1 m they would occupy a volume = 2.30 x 10^11 m^3. Assuming a density of 1 tonne = 1 m^3, and a concentration of PO4(3-) = 0.092%, we need:

2.30 x 10^11 x 0.092/100 = 2.13 x 10^8 tonnes of phosphate, i.e. 213 million tonnes.

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. Indeed, the ratio of algal phosphate to that present originally in the culture medium (i.e. 158/213) suggests that 74% of it is absorbed by the algae.

Now, world phosphate production amounts to around 140 million tonnes (noting that we need 213 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 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 53 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 phosphate rock output, and imports (of phosphate) are still needed.

The world total of 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 phosphate rock mineral. 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.

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.

A Hubbert 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 [1]. 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 [1]. 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.

Related Reading.
[1] "Biofuels and the fertilizer problem,", By Tom Phillpott.
[2] "Chlorella" - Wikipedia.
[3] "Biofuel from algae - Salvation from Peak Oil?


Anonymous said...

"..Marine Current Turbines, has successfully completed the first installation phase of the 1.2MW SeaGen Tidal System, previous post, the world’s largest grid-connected tidal stream system, into the fast-flowing waters of Strangford Narrows off the coast of Northern Ireland.."
Northern Ireland, even Wales and Canada (both in same link above) - this fight ain't over yet!

Daniel said...

That is why we will need to use waste water (sewage) to grow the algae. This water is very high in Phosphate. Phosphate pollution is the main contributing factor that wild algae blooms are out of control. Algae farming using municipal waste will kill two birds with one stone. One, clean the municipal waste. Two, grow bio-fuels and as a bonus, sequester CO2.

Professor Chris Rhodes said...

I like the idea of sea-power generally, while acknowledging the enormous amount of engineering that installing it on a large scale (from scratch) will entail. I'll check that link. I wrote an article about SeaGen recently and the prototype "upside-down" windmill type turbine to be placed at the Strangford Lough narrows.As I recall, "Strangford" means "Strong Ford" in Old Norse, as the currents flow quite fast there, above 7 knots.

Yes, that's my point - that we have to recycle phosphate from sewage, and indeed drain-off waters. We must do this to keep existing farming going in any case, even without growing algae for fuel, if we are to expect a decline in rock-phosphate from now on (according to the Hubbert analysis). In principle it could be recycled within the algae-growing programme, from year to year, but how exactly to get it from the algal waste, post oil-extraction, would need to be determined.



Anonymous said...

One of phosphate industry burdens is the phophogypsum obtained as byproduct, which contains some residual Phosphorus in it; with a major part consisting of calcium sulfate. I just wonder if this remaining phosphorus can serve, in a controlled manner, to farm the algae...


Professor Chris Rhodes said...

What are we talking about in terms of a concentration of P in phophogypsum? A couple of percent or more than that?

However, if that is available in quantity - and it sounds like it is if it's a by-product of the industry - then I think it could be very useful not just for nourishing algae but for all agriculture.



Judd said...

It might be of interest to note that state-of-the-art material processing technologies now exist that promise the distinct potential to reclaim and reuse a significant amount of the phosphate by-product derived from algae biofuel production as well as reclaiming waste phosphate from numerous other feed sources including manure and waste water plant residue. It is envisioned this reclaimed phosphate will not only be used as crop nutrients but also for the production of a distinctly superior quality, eco-friendly ceramic cement / concrete that replaces the environmental, quality problems associated with Portland cement and / or toxic epoxy binders, while being conveniently adaptable to present Portland cement production and application technologies. This still little known waste stream materials recycling research combined with ceramic cement appears to be a win/ win for all concerned. Regards, Judd

Professor Chris Rhodes said...

Looks great, Judd! Do you have a reference or a link you can pint me too,perhaps?

I ask out of interest in this important point but also that I am writing a book on the general subject of this blog and I would like to expand this topic into the positive!

I agree that recycling is key.



Anonymous said...

Yeah! Let's use up the last of the world's phosphates so that Joe Sixpack can keep driving his fat ass around in his SUV, while millions are starving worldwide.

Professor Chris Rhodes said...

It is telling that even if there is not a direct competition between food crops and fuel crops for arable land, the two scramble for the world's fertilizers.

So it all looks like we can't make the equivalent of 30 billion barrels of crude oil by this route either!

Looks to me like relocalisation of societies is inevitable; cutting the amount of fuel needed and producing food locally by non-fertilizer and fuel-input farming methods like permaculture.

In the present version, there are too many people, using to much of the world's resources, and what is the answer to that?


guayabapr said...

Great blog! good discussion! Have any of you considered growing certified organic marine algae in ponds with parallel production of organic Tilapia fish, that feed on the algae leftovers (after oil extraction and on the approximately 15-20% of the algae that stays in the saltwater after harvesting), and in turn create nutrients in the form of their bodily wastes, which are further refined by organic shrimp? That is what Bio-Lipidos de Puerto Rico is trying to do. We also use waste industrial CO2 as additional source of food for the algae. For more info, email me at

T. Hendlin said...

"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." No they are not necessarily energy intensive!
Properly designed it happens almost automatically. The livestock need to drink and already frequently have ponds and pools to drink from, many of which are positioned close enough to the quantities of animal poo to dirty the water anyway. Simply keep the muddy manure of the livestock pens around the ponds and the run off will automatically go into them or at-least transportation is minimized to yards and not miles. sure some light weight minimal redesign of most existing farms will be required but that can be as simple as re organizing the fences and digging the ponds int he right places. (plus its not an additional reduction in arable land since the live stocks trampled land is already used and not plant able with them on it.)

Likewise the simple act of composting the algae remains and using that compost then to feed the algae requires practically no energy input from our side except to transfer to a near by compost site and wait (once you get the process going the time delay between start of finish of each batch of compost becomes irrelevant as they each become "ripe" sequentially ensuring a constant stream of ready batches of composted algae feed).

Professor Chris Rhodes said...

O.K. that's very reassuring and looks to me as though we do have a potential or partial solution to hand.



Professor Chris Rhodes said...

Hi Monica,

I hadn't heard of the fish-solution but it looks like an integrated approach as is necessary to solve the problem.

Too much is wasted in terms of resources and energy and introducing such "feedbacks" is vital.



Oliver Glassl said...

Could it be the other way round? That in the future we will need algae to get the phospate for agriculture out of phosphate-rich ocean currents?

Professor Chris Rhodes said...

Dear Oliver,

a very good point. I guess this could all be part of a grand strategy to actually accrue phosphorus rather than use it up. Thus, this might help all of agriculture.

Thanks for your thought!


Professor Chris Rhodes said...

To VLFarming, thanks for alerting us to you blog, which looks very informative.



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