While it’s common to see advanced glass or plastic bioreactors displayed in articles about commercial algaculture, many facilities actually rely on open raceways or ponds instead. These in-ground and open-air features are often far more affordable to build and efficient to operate, especially on a large scale. Yet, bioreactors and other closed algae production systems are required for some circumstances where open equipment just isn’t suitable. Bioreactors are often necessary for the cultivation of pure stock for seeding larger raceways and ponds, which can be handled on-site or by a separate company. Compare the costs, benefits, and requirements of both types of algaculture to decide which is right for your facility.
Closed: Bioreactors, Tubes, Trays, and Panels
Closed algae systems include bioreactors, tubes, panels, and trays. These are all sealed devices that have one or more clear sides to allow light to penetrate so the algae inside can photosynthesize. Opaque bioreactors may be used for algae that are fed with sugars instead. These systems are almost exclusively used indoors because they’re more sensitive to damage than ponds and tanks. This adds to the cost of construction because of the need for additional greenhouses, covers, or buildings to protect them. However, they’re required for some kinds of food grade and pharmaceutical production since they offer the greatest protection against contamination or failure.
Advantages
- Provides the highest level of control over everything from the water quality to the exact amount of algae in the water
- Creates a higher concentration of algae particles per liter of water, making harvesting and dewatering slightly easier
- Prevents contamination from surface exposure or water runoff, which is a requirement for pharmaceutical and food grade production
- Makes the most efficient use of light by spreading the water out as thinly as possible without the issue of rapid evaporation
Disadvantages
- Higher cost due to the need for specialized materials, difficult construction methods, and custom designs
- Slow installation process that can take months to complete, especially for large facilities with many bioreactors
- Requires CO2 injection into the water supply since there’s little to no contact with the open air to allow for a natural gas exchange
- Limited size necessitates the use of multiple bioreactors or units, resulting in increased maintenance and repair work
- Can be difficult to impossible to find the glass and polymers needed to create large scale bioreactors, trays, or panels
- Harder to connect to existing sources of water like rivers or surface runoff
Open: Raceways, Ponds, and Tanks
Open algae systems are exposed to the air, taking advantage of the CO2 in the atmosphere and usually relying on free and abundant sunlight. This category includes both raceways designed specifically for growing biofuel and tanks with artificial lights designed for more controlled production of food or medical grade products. They rely on constant circulation from low power devices like paddlewheels or pumps rather than the high energy demands of CO2 infusion. However, they’re not as tightly controlled or protected from potential contamination as bioreactors. They also produce a solution with a lower concentration of algae per liter of water, adding a little extra work to the process of separating the two.
Advantages
- Much lower cost to build and maintain, with lower costs for both materials and labor
- Faster installation time so the cultivation of algae can begin within weeks to months
- Shallow depth keeps them easy to access for harvest, maintenance, and repairs
- Adaptable enough to be used in almost every situation, including above-ground when necessary
- Wider availability of the materials required for construction, such as flexible liners from BTL Liners
Disadvantages
- Open to contamination, which can be prevented with indoor placement or a cover
- Lower concentration of algae per liter of water
- Can be attractive to birds, other animals, or even humans and therefore require fencing and netting
- May produce odors that are unpleasant and spread to the surrounding area, especially if the algaculture facility doubles as a wastewater treatment plant
For most commercial production facilities, open designs like raceways make much more sense than exclusively using closed bioreactors. Bioreactors are simply too expensive to be used for the entirety of a large-scale operation. Raceways and ponds are easily constructed with flexible liners from BTL Liners. Our RPE products have the flexibility to conform to the tight curves and corners of algae raceways without developing cracks from wrinkling.