How to Use Algae as a Sustainable Biofuel Source

What are Algae?

Algae are a diverse group of aquatic organisms that have the ability to photosynthesize. There are microalgae that are unicellular and macroalgae that are multicellular, commonly known as seaweeds. Algae are found in both marine and freshwater environments and they form the base of aquatic food chains. Some key characteristics of algae:

• Algae contain chlorophyll and carry out photosynthesis.
• They are eukaryotic organisms, meaning their cells contain nuclei and organelles.
• Many species are microscopic, while others like giant kelp can grow to over 50 meters long.
• Algae growth is affected by sunlight, carbon dioxide, and nutrient availability.
• They grow rapidly and some doubling times can be as short as 3-5 hours.

Why Algae for Biofuels?

Algae have recently gained attention as a promising feedstock for renewable biofuels for several key reasons:

• Certain species of algae produce high amounts of lipids and hydrocarbons that can be converted into biodiesel or renewable diesel.
• Algae grow extremely rapidly and many species double their biomass within 24 hours.
• Algae require only sunlight, some species of bacteria, CO2 and water to grow, so they can utilize otherwise non-productive land.
• Algae production systems can be set up on non-arable land near power plants to utilize emitted CO2.
• Algae cultivation does not compete for land and resources with conventional agriculture like corn or soybeans.
• The oil productivity per land area of algae can greatly exceed that of conventional oilseeds.

In summary, algae are an attractive option for biofuels due to their rapid growth, high oil content, ability to utilize waste CO2, and limited compete for resources with food production.

How Algae Can Be Grown for Biofuels

There are two main approaches to cultivating algae for biofuels production:

Open Pond Systems

• This involves growing algae in large open raceway ponds mixed by paddlewheels.
• Open ponds provide a low cost production system but are less productive than closed systems.
• Key advantages: simple and inexpensive construction and operation.
• Challenges: more prone to contamination and weather fluctuations.

Photobioreactors (PBRs)

• Enclosed bioreactors made of transparent materials like glass or plastic tubes.
• Algae cultures are supplied with necessary inputs like nutrients and CO2.
• More productive and controllable environment than open ponds.
• Key advantages: optimized light delivery, temperature control, prevent contamination.
• Challenges: higher capital and operating costs than open ponds.

In summary, open pond systems are currently more economically viable for large scale algae production for biofuels, while PBRs allow for more controlled optimized growth.

How Algae Can Be Converted to Biofuels

Once algae have been harvested, there are two primary technologies to convert the algal biomass into usable biofuels:

Extraction and Transesterification for Biodiesel

• Algal oil is extracted from the biomass then put through a transesterification reaction.
• This converts the triglycerides in the algal oil into biodiesel - monoalkyl esters like fatty acid methyl esters (FAMEs).
• Biodiesel derived from algae shares similar fuel properties to conventional diesel fuel.
• It can replace or be blended with petroleum diesel in engines.

Hydrothermal Liquefaction to Biocrude Oil

• Whole algal biomass is processed under high temperature and pressure with catalysts.
• This breaks down the biomass and converts it into a biocrude oil that can be refined.
• Advantages are that it utilizes all the algal biomass instead of just oil.
• Produces a "drop-in" fuel requiring less processing than biodiesel.

In summary, algal biofuels can take the form of biodiesel, renewable diesel, jet fuel, and other biofuel products that serve as substitutes for petroleum-derived fuels.

Challenges for Economically Viable Algae Biofuel Production

While algae biofuels offer great promise, there are still challenges to make it economically viable on a large scale:

• Achieving very low cost, highly productive algae cultivation at large scale.
• Developing harvesting/dewatering systems that work for specific algal strains.
• Identifying algal strains with both high growth rates and high fuel precursor yields.
• Advancing conversion systems for improved efficiencies and economics.
• Integrating cultivation, harvest, extraction and conversion systems into a smoothly running, cost-effective overall process.

Continued research and development is still needed to improve algal biofuel economics and make it competitive with conventional petroleum fuels. But the high productivities possible from algae give it excellent potential in the longer term.

Conclusion

In summary, algae are emerging as a promising renewable feedstock for producing sustainable biofuels. With their rapid growth rates, high oil content, and ability to be produced with marginal resources, algae could ultimately help provide renewable alternatives to petroleum-based transportation fuels. Continued advancements and research are still needed, but algae-based biofuels have the potential to become a scalable green energy solution.