Scaling Algae Growth
for Biofuels


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In the pursuit of more sources of clean energy, microalgae are being investigated to determine if they can be a viable source of biofuels.

Algae are photosynthetic organisms that have been on the earth for millions of years and have adapted to brutal environmental conditions. Microalgae are simple forms of algae that produce many useful chemicals and thrive in nutrient-rich water, carbon dioxide, and sunlight.

Many in the industry are working on advanced biological aspects of native or genetically engineered organisms, attempting to improve their yield and robustness in various growth environments.

In addition, numerous others are looking at techniques for extracting and maximizing the obtainable proteins, carbohydrates, nutrients, and lipids that can be converted into biodiesel, green diesel, jet fuels, other fuels, and many other useful products such as food additives, cosmetics, bioplastics, and soil conditioners.

Solix Biofuels is one of the only companies focusing solely on the cultivation systems and extraction processes for algae, along with the equipment and methods of growing microalgae in the most productive and scalable way.

Their demonstration-scale photobioreactors have been growing algae outdoors continuously for more than two years, and have demonstrated the ability to produce the feedstock required to produce hundreds to thousands of gallons of lipid biocrude per year. They're now working to overcome the challenges of scaling required for this new industry.

Solix Biofuels has cultivated algae continuously in its Lumian AGS for three years with no culture crashes. Photo: Solix Biofuels

Complex Balance

Bryan McCarty, Solix Biofuels' vice president of engineering, described the cultivation technology as a modular, controlled-environment, outdoor system. They fill nearly transparent, closed panels with a blend of algae, growth media, nutrients, and salts.

As algae are exposed to sunlight in the growth panel, filtered air and CO2 is supplied through a lower vessel and bubbled up into the algae chamber in a process called sparging. Algae multiply rapidly as they are mixed in a productive reactor.

Optimizing algae growth is a complex process with many variables, combining biological and engineering processes. McCarty describes it as mainly a "water moving" challenge: how to move large amounts of water with minimal energy while maintaining optimal growing conditions, nutrients, and sunlight.

Because all types of algal growth systems require managing and moving a lot of water (the Solix system less so) they are still expensive, with the off-the-shelf pumps, centrifuges, and long distances currently used.

Solix is looking at ways to reduce both the movement and volume of water. They are also investigating cleaning and reusing the growth and other media, which has the benefit of generating less waste.

Location, Location, Location

When there is no sunlight, algae go into a period of respiration and nongrowth, so the system is shut down to a minimal sustaining level overnight. When it's cloudy, the growth rate will decline depending on the specific light intensity level available to the algae and how long the clouds are around.

Solix has designed its reactor to use both direct and diffuse light, so constant direct light is not required to maintain high average growth rates.

Solix is optimizing its technology to control the temperature environment in which the algae are grown. The company's operation outside of Durango, CO, is fully integrated with an adjacent facility that provides the opportunity to productively use the thermal benefits of wastewater, and also use waste CO2.

The ideal location is in a dry, sunny, flat desert, with a CO2 source such as a coal-fired power plant and a significant wastewater source. Solix is collaborating with researchers working on finding robust strains of algae that grow well year-round, in cold climates, or in regions with large temperature swings, such as a desert.

Scaling

Solix's AGS4000 commercial R&D-scale reactor processes about 4,000 L and has about 720 square feet of photosynthetic reactive area. Including support equipment, its footprint is about 4,000 square feet.

It provides sufficient equipment scale and tools to those in the algal space like startups, energy companies, and universities working on advanced biology processes. Using this scale reactor helps them understand how their organisms will behave outdoors, how productive they will be, and is more representative of a production process compared to a flask in the lab.

On a larger scale, Solix has built a pilot-scale demonstration facility with three-quarters of an acre of photosynthetic area forecasted to generate 1,500–2,000 gallons/year of biocrude, or an estimated several tons of biomass per year if the solids are included.

McCarty notes that due to limitations on time, investments, and costs, the technology is still in its early development stage. This type of photobioreactor has demonstrated high productivity and ultimately is intended to scale for large commercial production.

Debbie Sniderman is CEO of VI Ventures LLC, a technical consulting company.

The ideal location is in a dry, sunny, flat desert, with a carbon dioxide source such as a coal-fired power plant and a significant wastewater source.

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August 2011

by Debbie Sniderman, ASME.org