Algae bioreactors and photobioreactors

NASA launched the OMEGA (offshore membrane enclosures for growing algae) photobioreactor in 2009 as a project to grow algae in municipal wastewater and produce biofuel. The algae bioreactor would not compete with agriculture for land, fertilizer, or freshwater, offering a significant advantage over biofuels derived from corn, soybeans, and sugarcane.

Algae is an incredibly versatile plant which can be used in a wide variety of commercial and industrial applications from energy to oil to cosmetics, and it possesses impressive potential for carbon capture technology. Algae has been at used in small-scale versions of these applications for some time, but photobioreactors have unleashed greater potential for algae in all of these areas.

Until recently, algae has been grown in open air cultivation systems which are expensive and prone to challenges including water evaporation, predators eating the algae cultures, and a large land requirement. Photobioreactors, however, are closed cultivation systems, which solve these challenges while increasing production efficiencies and increasing yields.

What is a photobioreactor?

Algae biofuel tubes in a lab

Whereas bioreactors and fermenters feed sugar and oxygen to cell cultures and nutrients to microbes, photobioreactors feed light to photosynthetic organisms such as plants and algae.

Photobioreactors are not commercialized to the same degree as bioreactors, but are rapidly developing due to ongoing research and a better understanding of the many advantages of culturing algae. They are unique in their ability to effectively grow cultures using only wastes from other industrial processes: carbon dioxide, water, and heat.

Algae bioreactors enable carbon neutrality in a variety of applications

Algae for biofuels

Five thousand gallons of biofuel can be extracted from one acre of algae, making it comparable in efficiency to hydroelectric and geothermal power. Algae is highly productive, and can yield more than 80 times more oil per acre than fossil fuels, while reducing atmospheric carbon dioxide.

Algae for oils

Like corn and soybeans, algae can be refined into vegetable oils; and like petroleum, algae can be developed into cosmetics.

Algae for food – human and animal

Algae has a high protein content, and strains could be developed to have an even higher protein concentration. Unlike other plants, algae is a complete protein containing all amino acids. Additionally, it contains essential micronutrients, vitamins and minerals.

Algae for fertilizer

As algae is a living organism, it breaks down quickly in soil and releases nitrogen that is vital for soil health and helps other crops to grow.

Algae for carbon capture

Like trees, algae takes in carbon dioxide from the environment and releases oxygen as a metabolic waste product. However, algae grows much more quickly and requires less space than trees allowing for more efficient carbon capture.

Algae for plastics

Algae can be used to create compostable, environmentally friendly “green plastics” that provide strong structural support; and since algae can quickly break down, these won’t end up lingering in landfills like traditional plastic bags.

Algae for wastewater treatment

In addition to using untreated water to grow, algae can be used to treat industrial wastewater before it reenters municipal sewage. The inorganic nitrogen and phosphorous within the water streams then helps the algae to grow.

Advantages of algae bioreactors

Algae grows where no other crop will

Creating good growing conditions for algae is very simple. Algae can be grown on waste land that is not arable for corn, wheat, beans or other crops. It can also use water that is unsuitable for crops.

Growing algae is easy

Algae converts carbon dioxide into biomass using sun, water, and inorganic nutrients, including carbon dioxide. It is a unicellular organism, and can be grown in almost any climate or environment. Together, this makes algae very easy to culture in controlled conditions, even when optimal conditions are not achieved.

Algae bioreactors scale out effectively

While it is challenging to scale up photobioreactors, they can be scaled out quite effectively, allowing for higher yields using optimized lab-scale parameters. This modularization provides a large degree of process redundancy. While scale-out is likely infeasible for biofuel applications, which inherently require large batches, it is a reasonable approach for high-value, algae-based products such as cosmetics.

Energy from algae is fully renewable

Fossil fuels are rapidly depleting, and wind and solar energy are only available as environmental conditions permit. In contrast, algae can grow quickly and efficiently year-round, in almost any environment, and it can be transported using infrastructure already in place from oil, natural gas, and biofuels.

In fact, algae is often a carbon negative energy source. In 2019, the Eos Bioreactor was launched. Taking up only 21 square feet, it was able to sequester the same amount of atmospheric carbon as an acre of trees while producing usable biomass.

Challenges of growing algae in photobioreactors

Scale-up tactics are still in development

Best practices for scaling up algae in commercial photobioreactors are still in development. Critical process parameters such as light efficiency, carbon dioxide loss, mixing efficiency, and oxygen removal can all be optimized in the lab, but have not been successfully scaled in tandem.

Algae photobioreactors require uniform light distribution

Yield in photobioreactors can be measured as biomass productivity per unit of incident light. Light needs to reach all layers of algae in the reactor for uniform growth, penetrating through the self-shading that occurs. If too much light reaches the outer layers, and insufficient light reaches the inner layers, none of the culture will grow well.  The results of a 2015 experiment indicate that this challenge can be overcome by distributing optical fibers throughout the culture medium.

Photobioreactors have yet to achieve economies of scale

Because of the above challenges, photobioreactors have not yet been able to achieve economies of scale. Although there are clear indicators that this process will become significantly cheaper once it scales efficiently, the current required capital expenditures are often a barrier to entry.

Monoculture – with variations

As with any other crop, growing monocultures in algae bioreactors leads to risk of pests, pollution, and catastrophes affecting the entire supply. However, all living cultures, including those grown in photobioreactors, are subject to variations which can effect quality, without mitigating the risks of a monoculture.