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Algae have great potential as lean, green, alternative fuel machines. Well, maybe not so lean, considering their ability to accumulate oil is precisely what makes them valuable as a biodiesel feedstock. Biodiesel is produced by converting the triacylglycerols in plant and animal fats into fatty acid methyl esters (FAME) through a simple transesterification reaction. (See Biodiesel backgrounder for more information.) Biodiesel/FAME can be used in place of, or blended with, petroleum-based diesel fuel. Biodiesel derived from algae oil is still a small-scale endeavour, but it is a front-runner in the race to become the newest feedstock on the biodiesel block.
Algae Biodiesel 101:
Algae belong to a heterogeneous group of non-plant photosynthetic organisms that make sugar and oxygen from water, CO2 and sunlight. Some are large and multicellular, such seaweed, but many are microscopic and unicellular, such as the green microalgae that are grown for biodiesel production. Green algae can grow very quickly, and some species accumulate oil until it is more than half their mass. To make biodiesel, the algal oil is first extracted, either mechanically by pressing or chemically using solvents. Then, it undergoes transesterification just like canola oil or waste cooking grease to produce algae-derived FAME.
Just like biodiesel feedstock crops like canola, algae can be ‘farmed.’ Their requirements are not qualitatively different from the green algae that grow in ponds, swimming pools and aquariums. They need water, sunlight, CO2 and nutrients like nitrogen and phosphorus. There are two main ways that algae are cultivated: open ponds and closed bioreactors. Outdoor open ponds are like aquatic raceways with the water continuously flowing to circulate the algae and ensure uniform exposure to sunlight. Open ponds are susceptible to water evaporation and contamination by undesired species of algae. Closed bioreactors with solar panels provide a controlled environment for algae cultivation, so growth and oil accumulation can be maximized, but they are much more expensive to build and maintain.
The Pros: Are Algae Little Green Superheroes?
Here are a few potential advantages to using algae instead of oilseed crops for biodiesel production.
- Algae have higher oil content, per cultivated area, compared to oilseed crops like canola. Exactly how much more oil is debatable, but a conservative range may be two to ten times more.
- Algae don’t compete with crops for growth on high-quality agricultural land.
- Commercial-scale algae biodiesel requires a lot of CO2 to support photosynthesis, but the gas can be supplied by capturing industrial waste CO2. A Canadian company called Pond Biofuels has partnered with a cement manufacturer in St. Mary’s, Ontario to capture their waste CO2 for algal bioreactors. It’s a small-scale project now, but Pond Biofuels has its sights set on commercialization.
- Green algae need a lot of water, which is a valuable resource. A research project run by NASA has recently demonstrated that algae can be grown in municipal wastewater in floating plastic bioreactor tubes. As they grow, the algae clean the wastewater by extracting nutrients. The algae can then be used for biofuel production.
The Cons: Are The Little Green Superheroes Ready for Primetime?
A recent report by the U.S. National Research Council questions the sustainability of algal biofuels. Two main concerns about scaling up algae cultivation are the large volume of water and the large amount of nutrients (nitrogen, phosphorus and CO2) required. The innovative strategies mentioned above, like capturing industrial waste CO2 and using nutrient-rich wastewater, as well testing new strains of algae and different growth conditions, may be the key to unlocking algae’s full biofuel potential. The National Research Council of Canada has invested in algae research at the Institute for Marine Biosciences in Nova Scotia.
Algae Biodiesel Makes a Brief Debut at the Pumps
For the month of November 2012, algae-based biodiesel was available at select fuels stations in California. This pilot project used algae biodiesel produced by Solazyme Inc., and tested the market for expanded commercialization. Solazyme’s algae technology bypasses the need for sunlight and photosynthesis by growing the algae in closed, dark bioreactors and feeding them sugar from plant biomass.
Algae Biofuels beyond Biodiesel
Algae’s high oil content makes them ideal for biodiesel production, but there are other ways to harness algae energy. For example, they can be dried into ‘algae coal’ and co-fired with fossil coal in power plants. Algae can also be used as a substrate for anaerobic digestion to generate biogas. This technology uses bacteria to break down organic material in the absence of oxygen (anaerobic). The bacteria produce methane biogas, which can be combusted for energy. The future looks green – and possibly slimy.
- For an interactive animated slideshow about algae biochemistry:
- For more information about Pond Biofuels:
- For an article about the partnership between Pond Biofuels and St. Mary’s Cement:
- For more information about NASA’s algae and wastewater project:
- For more information about the U.S. National Research Council’s report on unsustainability of algae biofuels:
- For more information about the National Research Council of Canada’s Institute for Marine Biosciences algae research:
- For more information about Solazyme’s algae biodiesel:
- Article from Guelph Engineering Journal (2008) with a good overview of algae as a biodiesel feedstock:
- Editorial from Biofuels about the challenges facing the commercialization of algae biofuels: