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Lifecycle Study Finds Algae as Bioenergy Feedstock Has Higher Environmental Impacts than Conventional Crops in Energy Use, GHG Emissions, and Water Use; The Importance of Using Waste Streams

Schematic of systems considered in the study. Model scope includes all upstream processing of biomass material; conversion to liquid or solid fuel is intentionally excluded. Credit: ACS, Clarens et al. Click to enlarge.

Terrestrial bioenergy feedstock crops such as switchgrass, canola and corn have lower environmental lifecycle impacts than algae in energy use, greenhouse gas emissions, and water regardless of cultivation location, according to a new lifecycle assessment by researchers at the University of Virginia. Only in total land use and eutrophication potential do algae perform favorably. A paper on the study was published online 19 January in the ACS journal Environmental Science & Technology.

The researchers determined the impacts associated with open pond algae production with a raceway configuration using a stochastic life cycle model. The large environmental footprint of algae cultivation is driven predominantly by upstream impacts, such as the demand for CO2 and fertilizer, they found.

The scope of the analysis included those processes required for cultivation of biomass. For all crops, the entire plant was used to facilitate comparison on a total energy basis. Biofuel conversion processes were excluded from the scope of the analysis.

Five Life Cycle Burdens for Production of One Functional Unit of Energy (317 GJ) Algae, Corn, Canola, and Switchgrass in Virginia
 land (ha)energy
(MJ) x 104
(kg CO2e) x 104
(m3) x 104
(kg PO4- equiv)
algae 0.4 ± 0.05 30 ± 6.6 1.8 ± 0.58 12 ± 2.4 3.3 ± 0.86
corn 1.3 ± 0.3 3.8 ± 0.35 -2.6 ± 0.09 0.82 ± 0.19 26 ± 5.4
canola 2.0 ± 0.2 7.0 ± 0.83 -1.6 ±0.10 1.0 ± 0.14 28 ± 5.8
switchgrass 1.7 ± 0.4 2.9 ± 0.27 -2.4 ± 0.18 0.57 ± 0.21 6.1 ± 1.7
The standard deviation of each value is also presented (±).

In modeling algae production, the researchers selected open ponds as being the most promising option at present. They assumed that fertilizers and flocculants were added as water is pumped into or out of the ponds so that no additional mixing is required. Harvesting was assumed to proceed via a combination of flocculation and centrifugation, consistent with pilot-scale demonstrations and conventional practice for the dewatering of biosolids during municipal wastewater treatment. CO2 was bubbled into the ponds via an automated control system whereby the CO2 was added to the medium to maintain dissolved gas levels and pH at a constant level.

Land use is one impact in which algae offers a clear and appreciable improvement over corn, canola, and switchgrass. Algae cultivation uses land roughly 3.3 times more efficiently than corn, 4.3 times more efficiently than switchgrass, and 5 times more efficiently than canola. If corn were harvested only for the kernel, as is common practice, this disparity would be even larger since more land, roughly 100% more, would be needed to grow the same amount of biomass.

Although the improvement offered by algae is less dramatic than has been suggested previously, the results suggest that algae cultivation will be less limited by land availability than conventional crops. The land use estimates indicate that algae cultivation on roughly 13% of the United States’ land area could meet the nation’s total annual energy consumption. In contrast, use of corn would require 41% of the total land area, while switchgrass and canola would require 56% and 66%, respectively.

The land use changes implicit in large-scale bioenergy deployment are expected to have important implications for climate change and other impacts. These so-called ‘indirect’ changes are associated with conversion of arable land into production and were not included here. The focus of this work is to provide a comparative tool for already cultivated arable land, although future decisions to deploy bioenergy should consider the large-scale implications of land use changes.

—Clarens et al.

The team found that the life cycle impacts of algae cultivation are sensitive to several inputs that have been largely overlooked to date: the availability of renewable sources of nutrients and carbon dioxide. The model is largely insensitive to inputs widely associated with algae productivity such as water and sunlight availability.

In practice, they said, first-generation algae ponds will supply their nutrients and CO2 from fossil-based sources, with almost all commercially available CO2 coming from the steam reforming of hydrocarbons, and reactive nitrogen being produced by the Haber-Bosch process.

To reduce the environmental impacts of algae production, the authors said, flue gas and, to a greater extent, wastewater could be used to offset most of the environmental burdens associated with algae. To demonstrate the benefits of algae production coupled with wastewater treatment, the model was expanded to include three different municipal wastewater effluents as sources of nitrogen and phosphorus. Each provided a significant reduction in the burdens of algae cultivation, and the use of source-separated urine was found to make algae more environmentally beneficial than the terrestrial crops.

To reduce the impacts of algae cultivation to make it on par with terrestrial crops, producers will not only need to decide to use waste streams, they will have to develop means by which to deliver these waste streams to their production facilities since these are generally not available. The need to minimize the upstream impacts is the first overarching outcome from this analysis.

The second overarching outcome is that downstream processing is unlikely to change the life cycle assessment for the entire fuel cycle given how large the cultivation differences are...the huge impact differences reported here suggest that at a minimum cultivation will be a significant part of the overall life cycle burden. This work is not intended to supplant important future analysis in other life cycle stages. However, an exhaustive study of existing and proposed conversion technologies does not change the realities of the cultivation impacts. The authors anticipate that such analysis will find algae to be easier to convert into liquid fuels than some of the other biomass sources studies here because of their inherently high lipid content, semi-steady-state production, and suitability in a variety of climates.

—Clarens et al.


  • Andres F. Clarens, Eleazer P. Resurreccion, Mark A. White and Lisa M. Colosi (2010) Environmental Life Cycle Comparison of Algae to Other Bioenergy Feedstocks. Environ. Sci. Technol., Article ASAP doi: 10.1021/es902838n



Lets see the Assumptions

" In practice, they said, first-generation algae ponds will supply their nutrients and CO2 from fossil-based sources, with almost all commercially available CO2 coming from the steam reforming of hydrocarbons, and reactive nitrogen being produced by the Haber-Bosch process. "

at all over reaching?

As has been discussed before bioenergy seems to more efficient used for direct electricity production rather than liquid fuel production. Accordingly, a closed loop analysis would be in order with the furnace waste providing the CO2 and nutrient input for the system.

Will S

The bioreactor needed to extract the oil from the algae 'mash' could use natural gas or the bio-oil itself, with the waste heat recaptured for use by the bioreaction process and the CO2 reused in the ponds themselves.

Wastewater use for fertilization has already been used, and in Virginia itself, no less;



No mention of making alcohols or animal feed from algae remnants as coproducts?

Aren't there some new analyses that say using algae with lower oil content makes for a more robust loop if you sell all the coproducts?


Algae farms using just "...13% of the United States’ land area could meet the nation’s total annual energy consumption. In contrast, use of corn would require 41% of the total land area, while switchgrass and canola would require 56% and 66%."

And yet they conclude that algae would have a higher environmental impact?

Algae production is at such an infantile stage that it is of very little value to release a study like this.


I wonder who funded this study. Some of their assumptions and conclusions seem weighted.


Not only 13% of the United States' land area, but it will be desert area, since that's the area with most abundant sunshine and cheapest land. (though you need some pipes for delivering (sea)water and CO2)


The problem with this study is that it uses open-pond methods for algae growth for comparison. Its an old and unproven system.

Open-ponds are ill suited for algae growth over the long run. The future is in closed bioreactor systems. Moreover, the yield on a closed-system is multiple times higher then the archaic open ponds.

Especially in regards to newly engineered strains that are being designed by people like Craig Venter and Synthetic Genomics (of the Human Genome Project fame). These engineered strains can't be put in open-ponds, because they are open, and because they have a high risk of contaminating natural algae. A closed system is required for the next-generation of high-yield strains.

The problem with closed bioreactors is that they are still too early in development. Early examples are just starting to show up.

If anything, this study is far too premature in judging algae as a source of energy being that algae-based biofuels and the technology involved in it are only starting to be developed, and comparing a 50+ year old open-pond system as a measure of efficacy is beyond silly.


Good points about open pond - problems noted 30 years ago in the Aquatic Species studies.

We might also look at who funds this study - American Chemical Society. Their agenda includes opposition to Open Access science. And ACS owns and operates the ACS Petroleum Research Fund - a $500M fund to conduct research such as this.

ACS-PRF is charged with supporting "advanced scientific education and fundamental research in the petroleum field," including any area of pure science that may lead to further research directly impacting petroleum.

Aureon Kwolek

I wouldn’t put too much stock in this study. It gives you the false impression that algae does not measure-up. That’s because it’s based on narrow tunnel vision of how an algae installation is designed. How ‘bout Solazyme’s heterotrophic algae growing system, feeding biomass sugars in dark tanks, at up to 1,000 times more concentrated algae production – Not covered by the study. How ‘bout Algenol’s method, now going into commercial production, that perpetually extracts ethanol, without killing the algae – Not covered by the study. How ‘bout “Energy Quest”, a planned biomass burn electric power plant, integrated with an onsite algae to biodiesel plant – Not covered by the study. How ‘bout algae production integrated into the “Green Plains” corn ethanol plant, mitigating onsite CO2, waste heat and effluent waste water – Not covered by the study. And there are numerous other examples.

Algae production is not limited to the narrow assumptions made by the study. It’s much bigger than that and getting bigger yet. What started out several years ago with a handful of companies, is now several hundred companies, all using different methods. Furthermore, using a centrifuge to dewater algae is energy intensive old technology. That is being replaced with new state of the art dewatering methods that cost less than 2 bucks a ton, a small fraction of what it costs to use a centrifuge. The data used in the study is outdated.

I agree with another comment – that algae is still in its infancy and changing rapidly. So why bother with studying old production methods, when we are developing all kinds of new methods and integrations – that will probably be significantly more efficient and have a much better footprint than current technology. Put this study in the history column.

Aureon Kwolek

Defending Biofuels

Andres Clarens, an assistant professor in the Civil and Environmental Department, University of Virginia, is the lead author on this algae study.

Clarens not only bashes algae, he also bashes corn ethanol and soy biodiesel. He falsely claims that the 2008 spike in corn prices and food prices was caused by corn demand for ethanol – the typical fuel vs food myth. In that same year, we produced 2 billion gallons more ethanol than the previous year, increased our corn exports by 20%, and Doubled our exports of high protein distillers grains, the corn ethanol byproduct.

Dr. Antonio Bento, Associate Professor, Applied Economics and Management Program at Cornell, has a clear and accurate understanding of the economics of biofuels. Dr. Bento says: Commodities Speculation on Wall Street and escalating crude oil prices caused everything to go up in price, including food, fuel, and commodities. Food prices are directly proportional to energy and fuel prices, which determine transportation and production costs. Corn ethanol and soy biodiesel have a very minor impact on food prices. In fact biofuels compete with and displace petroleum based fuels, and they put downward pressure on the cost of fuel – Especially when biofuels are shipped directly to retail blender pumps.

On the other hand, Clarens thinks that using corn for fuel is ethically wrong, because it diverts food from hungry human mouths. Thus, his bad advice is to produce food and fuel separately. Clarens obviously doesn’t understand the economics. Nobody goes hungry because we take the starch from 25% of our feed corn crop to make ethanol, and produce co-product livestock feed, corn oil, and a biomass waste resource – Using feed corn that is not suitable for human consumption. Food, fuel, and fiber production is integrated and synergistic, not separate.

We have a huge surplus of corn, which makes up about 20% of the entire corn crop. This is exported and used mostly to feed foreign livestock for upwardly mobile populations, such as India and China. If you want to feed the hungry, you can buy corn anywhere in the world for about 7 cents a pound. We have plenty to sell. That is, if you can afford to ship it across the globe.

The roller coaster prices of crude oil and transportation fuels have the biggest impact on global food prices. The second biggest impact on corn prices is the demand for livestock feed, 4 times higher than the amount used for corn ethanol. Corn demand for ethanol is a distant third, and that is offset by the increasing value of the co-products.

Clarens gets his facts wrong. He states that biofuel refineries are using petroleum to convert corn into ethanol. They’re not. They’re using natural gas, and a good share of that is domestic natural gas that displaces imported oil. He also says: “By the time you get done, you’ve used almost as much petroleum to make ethanol that you would have if you just put the oil straight into your car.”

The fact is, based on the most up to date information shown in the 2009 Nebraska-Lincoln study, the energy return on corn ethanol is in the range of 1.5 to 1.8 for the average refinery, and a 2.2 return for biogas integrated refineries.

The energy return of corn ethanol will improve further, because we are beginning to take corn biomass residues and use them for CHP refinery production power, or to make addition ethanol. And we are also beginning to adapt ethanol refineries with a process that extracts corn oil from the byproducts (Greenshift). Both of these upgrades, and other cutting edge technologies in the works, will drive the energy return higher and spread the environmental impact across more co-products and higher productivity.

We are also beginning to see farmer-produced biodiesel fuel going into tractors. And tractors may also be built with higher torque ethanol-optimized engines with diesel-like power, using cheap ethanol that was made locally. High torque Plug-in Hybrid tractors with range extender ethanol-optimized engines, and highly efficient “direct ethanol” fuel cell powered tractors are also a possibility. These may be powered by 50-50 ethanol-water fuel processors generating hydrogen onboard the vehicle. Locally made biofuels may gradually displace shipped-in petroleum based fuels used for agriculture.

This is also in response to a related article in “Biofuels Journal” called: “University of Virginia Researchers Find Algae Biofuels Have Larger Environmental Footprint Than Other Feedstocks” (They Don’t) – The above is a rebuttal to the unjustified biofuel bashing expressed by the author of the same study.

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