It’s not enough to simply dig a pond, fill it with water, and sprinkle in an algae sample. Open ponds used for algaculture need constant water mixing, the appropriate depth, and accurate projections of the water evaporation and loss rates. If you plan to grow algae to use in a bioreactor system to generate power, the hybrid option also has some features to consider while designing the system. No matter the size and volume of your algae ponds, these important factors should all guide its design and installation.
Mixing Patterns
Unlike plants floating on rafts or fish that move through the water, algae are highly limited in their ability to move around. Some microalgae species do have flagella to slowly creep across an open expanse of water, but most are moved by the current and turbulence alone. This is why mixing the water constantly, at least during daylight hours, is an essential practice in every kind of algae pond. Mixing the water with a vortex generator, spray pipe, pumping system, or other method, ensures that all algae gets a chance to reach the surface and absorb as much sunlight as possible. Without the right mixing pattern, growth slows and you’ll achieve much lower harvest totals than you’re expecting. There are both continuous and semi-continuous water mixing systems available today, with each providing different benefits to specific algae species.
Depth
Deeper ponds aren’t necessarily better for algaculture due to the diminishing growth return rate as algae gets further away from a light source. For example, a five-foot deep fish pond will only grow algae rapidly in the first few inches of water. The lack of light and carbon dioxide exchange in the deeper water limits growth substantially. Most algae ponds are as shallow as 2 inches or as deep as 40 inches. Seaweed and other macroalgae can grow in ponds that are a few feet deep, while microalgaes tend to grow faster in shallow ponds, due to the increased light exposure and faster mixing rates. Depth should be determined before you choose a mixing pattern and equipment since some methods only work well in either deep or shallow designs.
Kinetic Studies
For the most advanced algae growth system, perform a series of kinetic studies on each pond design before choosing your final plan. Kinetic studies involve creating a digital model of the pond and then running various scenarios to explore how different mixing methods will affect the water. Thanks to the complexity of fluid dynamics, it’s not as simple to choose a water mixing system as it is to size a pump or filter. Commercial operations that aim to optimize their production and profits will find this design step well worth the investment.
Water Evaporation Rate
As long as the algae ponds are properly lined, the main water loss should occur through evaporation. Since algae ponds tend to be very shallow compared to fish or retention ponds, they also feature higher rates of evaporation. Greater surface area and more shallow depths directly correlate to more rapid water loss. The need for constant exposure to sunlight also increases the evaporation rate. Since algae can stop growing or die-off rapidly if the ponds dry out too much, it’s essential to track your evaporation rate and top up the ponds weekly, or even multiple times a week as needed. Raceway designs that feed the ponds with a constant flow of water from a local river or stream generally eliminate the need to do this, although you’ll still need to determine the evaporate rate to be safe.
Hybrid Systems to Feed Bioreactors
It is possible to combine both open and closed designs by developing a two-stage hybrid approach to algaculture. Open ponds are used to grow algae as rapidly as possible with free sunlight, and then the algae is transferred indoors to closed bioreactors to generate power. By using a steady supply of mature algae rather than trying to culture colonies in the bioreactors, these hybrid systems often achieve greater yields than strictly closed systems. However, they are tricky and do run a higher risk of contamination as algae is transferred from open to closed equipment.
BTL Liners is ready to help you as you design your algae pond and build a business around algaculture. If you’re looking for help on choosing a liner, contact one of our team members to find the product that will be fit your needs.
