Commercial Cultivation of Algae
All algaculture requires three basics: water, light and nutrients.
Water's the easiest. It doesn't need to be potable; different types of algae grow nicely in fresh water, salt water and dirty water. Sunlight, because it's free, is the preferred light. But sunlight reaches only 3 or 4 inches (7 to 10 centimeters) into a mass of algae, so growers must agitate the algae to expose all of it to the light [source: Chemeurope.com]. The main nutrient is carbon dioxide, which can come from the air or other source. Agitation or bubbling dissolves it into the water. The grower must supply other nutrients, like nitrogen and trace elements, if they aren't already in the water.
There are three basic systems for cultivating algae, each with its advantages and disadvantages:
- Open pond: The simplest and cheapest way to grow algae is in large, shallow ponds. The water is often divided into concentric lanes or raceways, with paddlewheels to move the algae mixture in a circle. This helps bring algae to the surface, where they're exposed to light, and mixes nutrients and carbon dioxide into the liquid. The open-pond method produces less algae biomass than other methods. It loses water to evaporation, so more must be added. And it allows for contamination by predators or undesirable algae.
- Closed pond: This method is similar to an open pond, but the water is covered by a Plexiglas greenhouse. This raises the cost, but allows greater control of the process. It reduces evaporation and contamination and extends the growing season. Growers can raise algae year-round if the space is heated.
- Biophotoreactor: A completely closed system, the biophotoreactor consists of glass or acrylic tubes where the algae are exposed to light. Pumps move the water, nutrients and algae through the tubes and storage tanks. Some reactors automatically harvest the algae when they're ready. This approach gives growers the most control over the process and the most efficient way to produce algae biomass. But it's also the most costly to set up and operate.
All of these systems are designed for growing microalgae, the one-celled varieties that float in water. Growers usually cultivate macroalgae in the open sea. The water already contains the nutrients the algae need and provides good growing conditions. The traditional method was simply to harvest wild seaweed, and this is still done in coastal areas around the world.
With increased demand, growers began to cultivate seaweed. For some varieties, such as kelp, spores are attached to ropes that are then anchored in the ocean and the seaweed is allowed to grow. Other types grow from pieces of seaweed that are fixed to nets or deposited in pools.
Agriculture has been around for 10,000 years [source: Lienhard]. Algaculture is relatively new. Scientists and engineers are actively studying the best ways to raise algae efficiently. The harvesting of plants is another subject of intense research.