|Algae colors green the waters of this Tennessee catfish
farm. The best way to extract fuel from algae, however,
may be through using a totally enclosed “bioreactor.”
Editor’s Note: With every new technology there is a lot of hype, especially when it is green technology. Biofuel is no exception. In the realm of new green energy technologies not only is the holy grail of abundant energy held forth by entrepreneurs to investors as an irresistable temptation, there is also the claim that we will save the planet. Heady stuff.
We’ve been aggressively covering developments in biofuel for quite some time now, and we’ve learned a few things. First of all, using the best crops out there, such as palm oil for biodiesel and sugar cane for bioethanol, you will get an economically viable crop. But at 6,000 barrels of fuel per square mile per year, you will not get a substitute for petroleum. In fact, to replace worldwide petroleum use with biofuel you would have to consume 10.8 million square miles of farmland with the highest yielding biofuel crops, and there are only 5.8 million square miles of farmland on earth.
We’ve also learned that the biofuel boom is already having unintended negative consequences. It’s crowding out food production and driving up food prices in nations where many of the poorer citizens already can’t afford to buy enough food. It is also encouraging new rounds of deforestation in regions where deforestation for rangeland, farms and timber harvesting are still out of control. Clearly, biofuel is a new technology with potential, but it is also problematic. A conscientious environmentalist will undoubtedly make a nuanced appraisal of biofuel, not a total endorsement.
Now we have a new concept – factory produced biofuel. In the following assessment of biofuel produced in a “bioreactor” from algae, the pitfalls of producing biofuel from algae ponds is recognized, and then the author explains the potential to produce biofuel within illuminated, enclosed containers, infused with carbon dioxide. While much more needs to be learned, it is certainly possible this process could become economically viable, and could result in a far higher contribution from biofuel to the ever increasing fuel requirements of civilization. – Ed Ring
|Didymosphenia geminata, microscopic
algae once scarce, but now in many
streams and rivers of North America
(Photo: US EPA)
Algae are microscopic, single-celled plants, growing in an aqueous environment.
For growth algae make use of sunlight as energy source and simple inorganic nutrients, predominantly CO2, soluble nitrogen components and phosphates. For many years, there has been a theory that noxious flue gases produced by industries could be substantially reduced by using algae. The algal biomass produced can then be used for generating high-energy biofuel. In the case of the cement industry, the biofuel produced can be directly fired in captive power plants and kilns.
Characteristics of algae cultivation are:
- The productivity per area is 2 to 5 fold higher as compared with traditional agricultural crops and fast growing ‘energy crops.’
- Lower quality water can be used for growing algae, e.g. the effluent of biological waste water treatment facilities.
- Algal systems can remove CO2 (and NOx) from flue gases.
- Many algal species produce valuable products, such as colorants, polyunsaturated fatty acids and bioactive compounds. These ‘fine chemicals’ are applicable as a natural ingredient in food products, pharmaceuticals, food supplements and personal care products.
- After extraction of these valuable compounds the remaining biomass (approx. 80%) can be used for production of ‘green’ electricity and heat. Alternatively, microalgae can be used for the production of methylesterfuel (bio-diesel).
Finding renewable energy sources has been a top concern for many scientists around the world and algae based biofuel has emerged as a viable resource. At present there are two common methods for algae based biofuel production: open ponds and bioreactors. The major technical challenges of these systems are how to: sustain highest photosynthesis and biomass productivity, reduce cell damage by hydrodynamic stress, reduce costs in fabrication, installation, and maintenance, and increase the capability of the system to expand to an industrial scale.
From 1978 to 1996, the U.S. Department of Energy’s Office of Fuels Development funded a program to develop renewable transportation fuels from algae. The main focus of the program, know as Aquatic Species Program (or ASP), was the production of biodiesel from high lipid-content algae grown in ponds utilizing waste CO2 from coal fired power plants. The study demonstrated that more than 300 species of algae were well suited to the task. Gaseous emission was pumped through the base of a pond and algae grown on the surface. The project was eventually abandoned because of the difficulty in harvesting algae and high cost of energy required to agitate the pond to ensure sufficient algal exposure to sunlight. As photosynthesis efficiency is driven by complex cellular mechanisms that depend on having just the right exposure to light, past algal systems grew to be complex and ultimately too expensive for most industries to contemplate. They took the form of huge, shallow ponds with extensive pumping and distribution mechanisms.
GreenFuel Technologies Corp., a Massachusetts based research company, working in collaboration with theMassachusetts Institute of Technology (MIT), using the air-lift bioreactors for algal growth on flue gas, has succeeded in reducing the capital investment by streamlining the harvesting of algae, limiting the energy required to operate the system, automating many of the necessary controls (e.g., flow controllers and gas uptake), and minimizing the physical space required.
|SCHEMATIC OF AN AIR LIFT BIOREACTOR|
|Solid arrows indicate the direction of the gas flow;
open arrows indicate the direction of the liquid flow.
GreenFuel uses an implementation of an air-lift reactor (ALR), which is a type of pneumatic contacting device in which fluid circulation takes place in a defined cyclic pattern through channels built specifically for this purpose. The process, called photomodulation, rotates the algae in and out of the sunlight. On the basis of the ALR principles and the specific requirements of photosynthetic processes, a “triangular” ALR configuration was developed that is particularly suitable for algal growth. The GreenFuel bioreactor consists of a riser tube or channel, a gas separator, and a down comer tube or channel. The difference in the apparent fluid densities between the riser and down comer provides the driving force for liquid circulation. Air-lift reactors (ALRs) have great potential for industrial bioprocesses, because of the low level and homogeneous distribution of hydrodynamic shear.
In the GreenFuel Technologies beta system at MIT, a slipstream from the MIT Cogeneration Plant is passed directly from a sampling port on the stack into a bank of triangle-shaped bioreactors containing algae in a salt water growth medium. Each bioreactor is self-contained; the gas enters at the bottom two vertices, and makes a single pass though the tubular bioreactor before exiting at the top vertex. The bioreactor dimensions-approximately 8 feet tall by 6 feet long by several inches wide-are determined by the amount of time required for the gas to dissolve in the growth medium as it rises through the vertical and hypotenuse legs (The triangle design is patented by GreenFuel).
The GreenFuel team has been growing algae on the Cogen gases, and harvesting algae ‘crops’ daily. Algae reduced NOx day and night, regardless of temporal and weather conditions. The process is essentially an effect of the surface configuration of the algae cell walls. Even dead algae can reduce NOx up to 70 percent. The harvested algae can be used to generate biofuel products. A week-long evaluation by a third party called CK Environmental Inc. certified that over the seven-day test period, the GreenFuel beta system simultaneously removed 85.9 percent NOx (2.1 percent, regardless of weather conditions), and 82.3 percent CO2 (12.5 percent) on sunny days, or 50.1 percent CO2 (6.5 percent) on cloudy or rainy days. The testing methods conformed to EPA standards for measuring NOx and CO2 emissions.
The Academic and University Centre in Nove Hrady, Czech Republic developed a closed tubular photobioreactor. This “penthouse-roof” photobioreactor was based on solar concentrators (linear Fresnel lenses) mounted in a climate-controlled greenhouse on top of the laboratory complex combining features of indoor and outdoor cultivation units. The dual-purpose system was designed for algal biomass production in temperate climate zones under well-controlled cultivation conditions and for heating service water with surplus solar energy.
GreenShift Corporation has acquired rights to Ohio University’s patented cynaobacteria based bioreactor process for reducing greenhouse gases emissions from fossil-fuel combustion processes. Dr. David Bayless at OU designed a bioreactor based on a newly discovered iron-loving cyanobacterium (blue-green algae). In concept, this is very similar to GreenFuel Technology’s reactor. The algae grown in the bioreactor on 60 by 120-centimeter membranes of woven fibers resembling window screens interspersed between the Oak Ridge glow plates. Capillary action wicks water to the algae, fiber optic cables channel sunlight into the glow plates, and ducts bring in the hot flue gas. Spreading the cyanobacteria on membranes maximizes surface area for growth, minimizes water and optimizes the use of sunlight. The algae use the available carbon dioxide and water, giving off pure oxygen and water vapor in the process. The organisms also absorb nitrogen oxide and sulfur dioxide. A prototype is capable of handling 140 cubic meters of flue gas per minute, an amount equal to the exhaust from 50 cars or a 3 megawatt power plant. Once the algae grow to maturity, they fall to the bottom of the bioreactor and are used as feedstock and fertilizers. The biomass can also be utilized for producing biodiesel.
Future research in this area would involve determination of the operational and economic feasibility of such systems for organic biomass production from the viewpoint of cement industry. This would lead to sequestration of CO2 produced from cement manufacturing and production of biofuel as an alternate fuel.
Novakovic, G.V., Kim, Y., Wu, X., Berzin, I., and Merchuk, J.C., 2005. Air-Lift Bioreactors for Algal Growth on Flue Gas: Mathematical Modeling and Pilot-Plant Studies. Ind. Eng. Chem. Res. Vol. 44, pp. 6154-6163.
Sheehan, J., Dunahay, T., Beneman, J. and Roessler,P., 1998. A Look Back at the U.S. Department of Energy’s Aquatic Species Program Biodiesel from Algae. U.S. Department of Energy, Office of Fuels Development.
De Boer, A.J., and van Doorn, J., 1998. Combined production of chemicals and biomass with microalgae in a closed photobioreactor. ECN Contribution to the 10th European Conference: ‘Biomass for energy and industry’. ECN RX-98-003, pp. 27-29.
Reith, J.H., van Doorn, J., Mur, L.R., Kalwij, R., Bakema,G. and van der Lee, G., 2000. Sustainable co-production of natural fine chemicals and biofuels from microalgae. Conference Biomass for Energy and Industry, Sevilla, June 2000.
Bayless, D.J., et al., 2002. Enhanced Practical Photosynthetic CO2 Mitigation (http://www.netl.doe.gov/publications/proceedings/01/carbon_seq/5a4.pdf)
Masojídek, J., Papácek, S., Sergejevová, M., Jirka, V., Cervený, J., Kunc, J., Korecko, J., Verbovikova, O., Kopecký, J., `tys, D. and Torzillo, G., 2003. A closed solar photobioreactor for cultivation of microalgae under supra-high irradiance: basic design and performance. Journal of Applied Phycology, Vol. 15, pp. 239-248.
GreenFuel: Using Algae to Capture Emissions
Vision: The World Student Community for Sustainable Development, April 22, 2005
Greenshift Licenses Bioreactor Technology
Green Car Congress, December 12, 2005
Beta Test Set for Emission-Fighting Algae Bioreactor
Power Engineering International, November 2004
Blue Green Acres
Scientific American, August 29, 2005
Algae Emissions Reduction Concept Shows New Promise
Electric Light & Power, March 2005
About the Author: Ramesh K. Suri is the Joint President for Alternative Fuels & Raw Materials Business Develoment at ACC Ltd., reporting to the ACC’s Managing Director. After completing his studies in Chemical Engineering at IIT Delhi in 1970, Suri joined ACC Ltd. and has held positions in the areas of plant operations, industrial engineering, design & construction, commissioning, project management, administration and consultancy services for cement plants within India and abroad. Suri has served on various national and international committees including the Asia Pacific Partnership on Clean Development and Climate (APP), Regional CDM Initiative APAC, and the Thematic Advisory Group of TERI.