Algae are generated from sunlight, water, CO2, and nutrients as well as algal cultures. There are more than 30,000 species of algae. One of the major factors in the use of algae to generate fuels is choosing the best species for oil generation and developing methods for removing the oil and making it into a fuel. Fuels that can be made from algae oil are biodiesel, n-alkane hydrocarbons, ethanol, methane, and hydrogen. Algae can also be used for soil conditioners and agrochemicals such as fertilizers and proteins as well as fine chemicals and bioactive substances such as polysaccharides, antioxidants, omega-3 and-6 fatty acids, proteins and enzymes.
There are currently several applications for algae including: 1) algin – a thickening agent for food processing (brown algae), 2) carrageenan – foods, puddings, ice cream, toothpaste (red algae), 3) iodine (brown algae), 4) agar – growth media in research (red algae), 5) as food (red and brown algae), 6) plant fertilizers, and 7) diatomaceous earth – used for filtering water, insulating, soundproofing. Table 10.1 shows some additional applications detailing the species, end product, origin, and main way to culture the algae.
|Species||End Product||Origin||Main Culture Systems|
|Chlorella spp.||Health food||
Circular pivot ponds
|Spriulina spp.||Health food||
Extensive open ponds
|Crypthecodinium cohnii||DHA||USA||Heterotrophic cultivation (glucose)|
Tetraselmis spp. Pavlova spp.
|Aquaculture feed||Throughout the world||
The role of algae in the aqueous world is that they are the base of the aquatic food chain and are photosynthetic organisms. There is a symbiotic relationship between fungi and algae known as lichens. A lichen is a composite organism that emerges from algae or cyanobacteria living among filaments of a fungus in a mutually beneficial relationship. Their properties are plant-like, but lichens are not plants. Lichens help to cause the pigments of algae, reduce harmful amounts of sunlight, and kill bacteria. They can also serve as shelters, such as kelp forming underwater forests and red algae that form reefs.
Algae can have some negative impacts via eutrophication. Eutrophication is the ecosystem response to the addition of artificial or natural substances, mainly phosphates through detergents, fertilizers, or sewage to an aquatic system. It can also be caused by dense bloom of cyanobacteria or algae. These can cause impacts through 1) clogging of waterways, streams, and filters, 2) a decrease in water taste and quality, and 3) potential toxicification. Red tide is one event that can be caused by dinoflagellates.
So why make biofuels from algae? There are several reasons. Algae have high lipid content (up to 70%); they grow rapidly and will produce more lipids per area than other terrestrial plants (10-100 times). To grow algae, non-arable land (this can be thought of as land that is not typically used for farming) can be used along with saline or brackish water. Algae don’t have the same competition with generating food or feed as other oil producing plants. One of the most amazing features is the use of CO2 in growing algae; it helps grow algae significantly. It also provides nutrient (N, P) removal in agricultural and municipal wastewater. Table 10.2 shows a comparison of annual oil yield from a variety of plants and algae. Even microalgae with lower lipids content (30%) will generate 50.00 m3/ha, significantly higher than palm oil. (Mata et al., 2010)
|Source||Annual oil yield (m3/ha)|
|Microalgae (30% lipids)||59.00|
|Microalgae (50% lipids)||98.00|
|Microalgae (70% lipids)||140.00|