Algaculture is a type of aquaculture in which algae is cultivated. Although it is possible to grow seaweed, nearly all algaculture farms grow microalgae.
How does algaculture work?
Step 1: Isolate the desired algae strain
Algaculture farms typically grow just one type of algae. Water samples are taken from the wild and sent to a lab. If the correct strain is identified, the lab uses serial dilution to isolate it: water is added to the sample and then the sample is separated into several sections. Only the sample with the greatest content of desirable algae is kept. This sample is diluted and separated again and again until a water sample is created containing only the desirable algae.
Step 2: Build an environment for the algae to grow
Once an algae strain has been isolated it needs to be cultivated in either an open pond or a photobioreactor.
A photobioreactor is basically a sealed clear container. This prevents other species of algae from invading, but it also requires the addition of fertilizer and air or carbon dioxide.
Open ponds can be used if the environment is managed in such a way that the desired algae strain has a growth advantage, pushing out other organisms. Weather can have an effect on these ponds, limiting the growing season. However, they are much cheaper to build than photobioreactors.
Step 3: Maintain algae growth
Air or carbon dioxide will need to be pumped into the bioreactor to fuel the cells. Nutrients will also need to be added to the water, including potassium and phosphorus.
Algae can grow so thick that it prevents sunlight from penetrating the water, yet UV rays from direct sunlight can be fatal to these organisms. Tanks and ponds must be stirred using either air bubbles or paddle wheels to ensure the algae is neither cut off from sunlight nor overexposed.
Step 4: Harvest
The algae will need to be separated from the water using filters, centrifuges, or chemicals. In bioreactors the air supply can be cut off, killing the cells and forcing them out of suspension.
Why is algae grown?
The most familiar use for farmed seaweed is nori, the green paper-like sheets used to wrap sushi. Agar agar, a vegetarian replacement for gelatin, also comes from microalgae. The algae strain Spirulina is used as a dietary supplement and can be found in some shampoos.
Algae may soon be an important source of fuel. On a per-acre basis algaculture can produce ten times as much oil as an oil palm plantation and one hundred times as much as a soybean farm. Once extracted, this oil can be mixed with methanol to create methyl esters, commonly called "biodiesel." This fuel can be burned in conventional diesel engines.
Algaculture is also being looked at as a way to sequester carbon emissions from coal power plants. Pure carbon dioxide from the plant is pumped into the algae tubes increasing plant growth beyond what is available with regular air. The algae break down the CO2 creating glucose to fuel the cell and oxygen which is released into the atmosphere.
