Microalgae are a potential source of fermentable substrate. According to the conditions of cultivation, microalgal biomass can provide high levels of carbon compounds. These com­pounds are available directly for fermentation or after pre-treatment and may be used for eth­anol production.

Biogas is the product of the anaerobic digestion of organic matter and can be obtained from domestic sewage, animal waste, solid waste, or aquatic biomass, such as macro- and microalgae (Omer and Fadalla, 2003; Gunaseelan, 1997). The type of digestion using microalgal biomass processes can eliminate the biomass harvesting and drying and the asso­ciated costs (Vonshak, 1997).

The fatty acids that microalgae produce can be converted into biodiesel, which is a renew­able, biodegradable, nontoxic, and environmentally friendly fuel. Biodiesel has the advantage that it emits 78% less carbon dioxide when burned, 98% less sulfur, and 50% of particulate matter emissions (Brown and Zeiler, 1993).

Another promising biofuel is hydrogen. Photobiological hydrogen production can be in­creased according to the carbon content in the biomass. The microalgae are candidates for such a process because they produce hydrogen under certain conditions and can be grown in closed systems, allowing the capture of hydrogen gas (Benemann, 1997). This biomass can be burned to produce energy because the calorific value of these microorganisms is greater than that of some charcoals.