Introduction to Algae Biofuels
Algae biofuel is an exciting and rapidly developing field that utilizes algae as a renewable source of energy. Algae naturally produce oils and can be grown in large quantities to produce biodiesel, jet fuel, ethanol and other biofuels. Algae have many advantages over traditional crops used for biofuels:
- Algae have very fast growth rates and can double their mass in 24 hours. This allows for high oil yields per acre.
- Algae can be grown on non-arable land that is not suitable for food production. This avoids competition with food crops.
- Some algae can grow in saltwater, brackish water or wastewater. This reduces freshwater use.
- Algae utilize carbon dioxide as they grow, reducing greenhouse gas emissions.
- The composition of algae oils can be tailored based on growth conditions. This allows production of optimized fuels.
- Algae can produce other valuable co-products like proteins, nutraceuticals and fertilizers.
While algae biofuels show enormous potential, there are still challenges to overcome before they can reach commercial scale production. The keys will be increasing productivity and efficiency while reducing costs.
Selecting the Right Algae Strains
Choosing the optimal algae strains is one of the most important factors for profitable algae biofuel production. Ideal strains exhibit:
- Fast growth - Strains that multiply rapidly maximize biomass and oil yields.
- High oil content - Strains with over 50% oil content produce more fuel per biomass.
- Valuable co-products - Some produce proteins, pigments, vitamins, omega-3 oils or other byproducts.
- Resilience - Robust strains withstand temperature, pH and contaminant fluctuations.
- Ease of harvest - Strains that flocculate or float simplify harvesting.
Examples of promising algae strains include:
- Botryococcus braunii - This green algae can produce up to 75% oil by dry weight.
- Nannochloropsis - These saltwater algae are resilient and commonly used for aquaculture.
- Chlorella - Rapidly growing green algae that can double its biomass daily.
- Spirulina - Cyanobacteria rich in proteins, omega-3s and pigments like carotenoids.
Researchers continue isolating and genetically engineering algae to enhance biofuel performance. Maintaining biodiversity in culture collections preserves options.
Optimizing Growth Conditions
To achieve maximum productivity, algae growth conditions must be carefully controlled and optimized:
Lighting
- Natural sunlight is free but inconsistent. Artificial lighting allows 24-hour growth.
- Photobioreactors allow precise light levels and distribution.
- Optimal wavelengths and intensities vary between algae species.
Carbon Dioxide Delivery
- Elevated CO2 levels boost algae growth rates and yields.
- Flue gas from power plants can provide concentrated CO2.
- Careful pH monitoring is required to optimize carbon utilization.
Temperature
- Most algae grow best between 20-30°C. Temperature affects growth rate and oil content.
- Water temperature must be controlled, especially in open ponds.
- Closed bioreactors allow better temperature regulation.
Nutrients
- Nitrogen and phosphorus levels strongly influence growth and oil production.
- Fertilizers must be optimized for each algae strain. Deficiencies and excesses both reduce yields.
- Wastewater can provide key nutrients like nitrogen and phosphorus.
Cultivation Systems
Algae can be grown in open pond or closed photobioreactor systems:
Open Ponds
- Less expensive to construct than bioreactors.
- More prone to contamination and environmental fluctuations.
- Require large land areas with adequate sunlight and water.
- Most suitable for robust, fast-growing algae strains.
Photobioreactors
- Enclosed, light-harvesting vessels provide controlled conditions.
- More expensive to build but achieve higher productivities.
- Better for delicate algae strains and pharmaceutical products.
- Various designs (tubular, flat-plate, bag, etc.) are available.
Hybrid approaches that use cheap open ponds for initial biomass production followed by bioreactors for oil enhancement offer a balanced approach.
Harvesting and Processing Algae
Effectively separating algae from water is vital for efficient biofuel production. Common approaches include:
- Flocculation - Adding chemicals that bind algae together into larger aggregates that can settle or be skimmed off.
- Floatation - Bubbling air into tanks causes algae to float to the surface.
- Centrifugation - Spinning mixtures separates algae by density. Energy intensive but fast.
- Filtration - Membranes filter algae from water. Works well for filamentous algae.
- Electrocoagulation - Applying an electric field causes algae to clump together.
After harvesting, algae must be further processed to extract and refine the oils into finished fuels. This involves:
- Cell disruption - Breaking thick cell walls to access oils, often by high pressure homogenization.
- Extraction - Isolating oils from biomass using solvents like hexane or mechanical pressing.
- Conversion - Converting algae oils into biodiesel via transesterification or renewable diesel via hydrotreating.
Making Algae Biofuels Economically Viable
For algae biofuels to compete with petroleum, further innovations are required:
- Increasing algae productivity through genetics and optimized growth.
- Developing co-products like nutraceuticals and proteins to improve revenues.
- Improving harvesting/processing efficiency to reduce costs.
- Utilizing wastewater resources for key nutrients.
- Designing large-scale integrated production facilities.
- Leveraging carbon taxes and biofuel subsidies to support growth.
With continued research and sustained investment, algae-based fuels can become major contributors to transportation energy needs while significantly reducing net carbon emissions. The future is green.