How Algaculture Works

Why have algae generated excitement and attracted research investment in recent years? Like all green plants, algae contain chloroplasts in their cells. These tiny structures are charged with chlorophyll, a molecule that uses light energy to combine carbon and water into a simple sugar. The cells further transform some of these sugars into proteins and lipids or oil.

But if algae are doing the same thing as corn, wheat and apple trees, why bother raising them? After all, corn on the cob, sweet rolls and apple pie taste better than seaweed to most of us. Here are some of the things algae have going for them:

Attracted by all these advantages, algae cultivators have been working diligently to come up with efficient and economical ways to grow and harvest the plants. The cost factor is currently the great challenge that must be overcome to make algae commercially viable.

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:

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.

Harvesting microalgae means removing the microscopic plants from the water in which they grow and concentrating them into a paste. The grower then needs to remove the moisture, leaving a dense biomass. The minute size of microalgae presents a problem when it comes to harvesting.

One method is filtration. The grower can run the water containing the algae through a cellulose membrane whose pores are smaller than the algae cells. This can be difficult because filters quickly fill up with algae and become clogged. Researchers are looking for better ways to efficiently filter algae.

Flocculation, another method of harvest, means getting the algae to clump together. Adding chemicals or types of algae that naturally clump can cause microalgae to form clumps that become easier to gather.

Another way to harvest algae is by flotation. Here, the grower uses compressed air to create a froth of bubbles and algae that brings the tiny plants to the surface where they can be skimmed off.

A centrifuge is yet another harvest method. Spinning a container filled with water and algae causes the algae to collect in one end.

In order to harvest their crops most effectively, algaculture growers sometimes combine these methods. They might use flocculation to form algae clumps, then separate them with flotation or a centrifuge. Coming up with a truly efficient way to harvest microalgae is a key to bringing down the cost of cultivation.

Harvesting macroalgae involves different problems. Gathering wild seaweed is a labor-intensive process. Some types of seaweed grown in controlled conditions can be gathered in nets. Kelp raised on ropes can be hauled out and hung up to dry. Kelp forests in shallow seas can be mowed by machines, taking off the tops of undersea kelp beds.

Once harvested, algae must be drained of its water and dried. A centrifuge can spin water out, but is relatively expensive. Some systems combine harvest and processing, spreading the algae on belt filters that let the water drain through, then removing more water using a capillary medium that draws water out of the biomass of algae.

The next step is to break down the cell walls of the algae in order to extract the oil inside. The algae are put through a screw or piston press. Chemicals, electromagnetic pulses or ultrasound may also be used to break down the cells. When the oil has been drained off, the remaining biomass is compressed into a cake to be used as to supplement animal feed or as a fertilizer.

Algae have found a wide range of uses, the most exciting ones in the energy field.

The buzz about algae is that it's an ideal source of renewable energy and could be the ultimate green fuel. Research by the U.S. government and companies like Boeing, Chevron and Honeywell are developing ways to make algaculture an economically viable foundation for a new generation of energy [source: Chemeurope.com]. Part of the attraction is the range of fuels into which algae can be converted.

Algae actually thrive on polluted water, which means they can be used for waste water treatment. Algae turn pollutants from municipal, industrial or agricultural waste water into usable byproducts like animal feed or biomass for conversion to energy. Algae naturally accumulate heavy metals for removal or recycling.

Because carbon dioxide, the greenhouse gas that contributes to climate change, is algae's favorite food, the plants can be used for carbon capture. They convert the gas to organic carbon compounds at a far faster clip than land plants. One pound (453.6 grams) of algae consumes 2 pounds (907.2 grams) of carbon dioxide [source: Edwards]. Feed the waste gas of a coal-burning power plant into a mass of algae, and they literally eat it up. Waste gas can be stored for permanent elimination from the atmosphere, or converted to fuel to cut the use of fossil fuels.

Algae continue play a role as human food and supplements. People eat seaweed in salads and sushi and take supplements made from the microalgae spirulina. Algae provide complete protein, omega-3 fatty acids and vitamins. Carageen is extracted from red seaweed known as Irish moss and used as a thickener.

Algae are also being used as feed for cattle and for marine animals like shrimp and shellfish. The biomass left after algae have been processed can sometimes be applied as organic fertilizer to farm fields. Algae find minor uses in cosmetics and pharmaceuticals as well.

Research into growing, harvesting and processing algae is advancing on many fronts. Given its immense value, there's no doubt that this simple "weed" will play a growing role in the future of our society and economy.

Before researching this article, I honestly didn't know that algae and seaweed were different forms of the same little green plant. I'm amazed at algae's potential in so many directions: food, energy, pollution control. Pilot projects seem to be popping up everywhere, from seaweed experiments in Long Island Sound to biodiesel efforts in West Virginia to a carbon-absorption project in Oregon. I've gotten the impression that we may very well be on the verge of an algae revolution.

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