The term Aquatic Biofuels refers to biofuels produced from aquatic photosynthetic organisms (mainly algae) and organic wastes of the fish industry.
Around the world, an urgent demand for alternative, sustainable fuels and feedstocks is growing due to rising oil prices and growing pollution concerns. Compared to other feedstocks, algae holds enormous potential as a high-yield source of biodiesel, ethanol and aviation fuels without competing for food supplies or arable land.
Algae are the fastest-growing plants in the world. Like other plants, they use photosynthesis to harness sunlight and carbon dioxide. Energy is stored inside the cell as lipids (the source for oil) and carbohydrates. Algae can be converted into biodiesel, ethanol, biocrude and aviation fuels.
Among biofuels projects, algae is commonly grown in two scenarios. The first is in ponds, and the second is grown in closed translucent containers called photobioreactors (PBRs).
In both cases the growth of algae requires a source of carbon, light, nutrients, and warm water.
Microalgae are currently cultivated commercially for human nutritional products around the world in several dozen small- to medium-scale production systems, producing a few tens to a several hundreds of tons of biomass annually. The main algae genera currently cultivated photosynthetically (e.g. with light energy) for various nutritional products are Spirulina, Chlorella, Dunaliella and Haematococcus.
Total world production of dry algal biomass for these algae is estimated at about 10,000 tons per year. About half of this produced takes place in mainland China, with most of the rest in Japan, Taiwan, U.S.A., Australia and India, and a few small producers in some other countries.
Microalgae biomass is also produced for live aquaculture feeds in systems that individually produce from a few kilograms to a few tons of biomass annually. Microalgae flourish in municipal wastewater treatment ponds, where they perform a waste purifying function, but harvesting of the algal biomass is generally not practiced, and where it is the chemical flocculants used to remove the algal cells limit further uses of the algal biomass, even for biofuels (e.g. anaerobic digestion for methane generation).
Finally, production of microalgae for nutritional products is also carried out commercially by dark fermentations (using starch or sugar, -rather than light energy and CO2) as in photosynthesis with a few thousand tons of algal biomass with a high content of valuable omega-3 oils, used mainly in infant formulas, produced by this route. This approach has also been proposed by at least one company as a near-term route for biodiesel production. However, here we emphasize photosynthetic processes and such fermentation systems are not discussed further.