How to Turn Algae Into a Viable Biofuel Source
Algae are one of the most promising sources of renewable biofuel. Unlike other biofuel crops, algae do not compete with food crops for land and can be grown with minimal freshwater. Algae can also produce much higher yields per acre than conventional crops. With some engineering innovations and process improvements, algae could become a major global source of transportation fuels. In this article, I’ll provide an overview of algae biofuels and explain the current methods for turning algae into viable biofuels.
Algae Varieties for Biofuel Production
There are thousands of different algae species, but only certain types are suitable for biofuel production:
Microalgae are single-celled organisms that typically grow suspended in water. The main microalgae varieties used for biofuels include:
- Green algae – A diverse group that includes Chlorella and Dunaliella salina. These algae produce oil and can grow in fresh or salt water.
- Diatoms – Single-celled algae with cell walls made of silica. Diatoms like Skeletonema costatum produce oils and can be grown in oceans.
- Golden algae – Primarily Prymnesium parvum, these algae produce lipids and grow quickly in brackish water.
Macroalgae are multicellular, seaweed-like algae. Common varieties include:
- Kelp – Large brown algae such as Laminaria that grow in cool ocean waters. Kelp can be processed into liquid biofuels through hydrothermal liquefaction.
- Sargassum – A brown macroalgae that floats on tropical seas. The sugars in sargassum can be extracted and fermented into bioethanol.
Microalgae tend to be better biofuel feedstocks than macroalgae because of their faster growth rates. However, macroalgae do not require cropland, so they can complement microalgal biofuels.
Algal Biofuel Production Methods
There are three main processes for generating biofuels from algae:
1. Extracting and Refining Oils
Most algae produce oils that can be extracted and refined into biodiesel or other fuels:
- Algae are grown in open ponds or closed photobioreactors.
- The algal oils are extracted using solvents like hexane or pressed mechanically.
- The oils then undergo transesterification, converting them into biodiesel.
- Further refining and blending produces green diesel, jet fuel, and gasoline.
This process is similar to first-generation biodiesel production using oil crops like soybeans. Algal oil yields per acre are estimated to be 10-30 times greater than soybeans.
2. Hydrothermal Liquefaction
This process uses heat and pressure to convert whole wet algae biomass into biocrude oil:
- Algae are grown and harvested like above.
- The algae slurry is pumped into the liquefaction reactor at 280-370°C and 1500-3000 psi.
- Under these conditions, the algae decompose into biocrude oil.
- The biocrude is then refined into finished fuels like diesel and gasoline.
Hydrothermal liquefaction breaks down all algae components, not just oils. This can boost fuel yields compared to extraction.
3. Fermentation into Ethanol or Butanol
Like other crops, algae can be fermented into alcohol biofuels:
- After growing algae, the carbohydrates are extracted from the cells.
- The sugars are fermented into ethanol or butanol using yeast or bacteria.
- The resulting alcohol is concentrated and purified into liquid transportation fuel.
Fermentation co-products like glycerin and leftover biomass can be processed into co-products.
Optimizing Algae Biofuel Production
Several approaches can help maximize productivity and efficiency:
- Bioprospecting to find naturally robust, oil-rich algal strains.
- Metabolic engineering to tweak algae genetically for better fuel yields.
- Open pond optimization through strains, paddlewheels, and nutrient recycle.
- Photobioreactor R&D to allow large-scale enclosed cultivation.
- Harvesting innovations like flocculation to separate microalgae cheaply.
- Co-product development for leftovers like proteins and glycerin.
With continued research, open ponds could one day produce 10,000-15,000 gallons of algal biofuel per acre per year. That’s over 10 times the yield of corn ethanol!
Algae have tremendous potential to sustainably supply renewable biofuels at a global scale. By tapping the incredible productivity of algae in well-designed systems, algal biofuels could displace a significant portion of fossil fuels for transportation while recycling carbon dioxide and avoiding competition with agriculture. With increased funding and research, revolutionary algal biofuel technologies could become a reality within decades.