1.1 Introduction

Billions of years ago the Earth’s atmosphere was filled with CO2. Thus there was no life on the planet. Life on Earth started with Cyanobacterium and algae. These humble photosynthetic organisms sucked out the atmospheric CO2 and started re­leasing oxygen. As a result, the levels of CO2 started decreasing to such an extent that life evolved on Earth. Once again these smallest organisms are poised to save us from the threat of global warming.

Algae, like corn, soybeans, sugar cane, wood, and other plants, use photosyn­thesis to convert solar energy into chemical energy. They store this energy in the form of oils, carbohydrates, and proteins. The more efficient a particular plant is at converting that solar energy into chemical energy, the better it is from a biodiesel perspective, and algae are among the most photosynthetically efficient plants on earth. A 1-ha algae farm on wasteland can produce over 10 to 100 times of oil as compared to any other known source of oil crop. Algae-based technologies could provide a key tool for reducing greenhouse gas emissions from coal-fired power plants and other carbon-intensive industrial processes.

Algae range from small, single-celled organisms to multicellular organisms, some with fairly complex and differentiated forms. Algae are usually found in damp places or bodies of water and thus are common in terrestrial as well as aquatic envi­ronments. Like plants, algae require primarily three components to grow: sunlight, carbon dioxide, and water. Photosynthesis is an important biochemical process in which plants, algae, and some bacteria convert the energy of sunlight into chemical energy.

Microalgae are fast-growing beasts with a voracious appetite for carbon dioxide. They have the potential to produce more oil per acre than any other feedstock being used to make biodiesel, and they can be grown on land that’s unsuitable for food crops (Demirbas 2009a).

A. Demirbas, M. Fatih Demirbas, Algae Energy DOI 10.1007/978-1-84996-050-2, © Springer 2010

Algae are simple organisms that are mainly aquatic and microscopic. Microalgae are unicellular photosynthetic microorganisms living in saline or freshwater envi­ronments that convert sunlight, water, and carbon dioxide into algal biomass (Ozkurt 2009). They are categorized into four main classes: diatoms, green algae, blue-green algae, and golden algae. There are two main populations of algae: filamentous and phytoplankton. These two species, in particular phytoplankton, increase in numbers rapidly to form algae blooms (Demirbas 2009b). Like higher plants, they produce storage lipids in the form of TAGs. Many species exhibit rapid growth and high productivity, and many microalgal species can be induced to accumulate substan­tial quantities of lipids, often greater than 60% of their dry biomass (Sheehan et al. 1998). Microalgae are very efficient solar energy converters and can produce a great variety of metabolites. Humans have always tried to take advantage of these proper­ties through algal mass culture.

To achieve environmental and economic sustainability, fuel production processes are required that are not only renewable but also capable of sequestering atmo­spheric CO2. Currently, nearly all renewable energy sources target the electricity market, while fuels make up a much larger share of the global energy demand. Biofuels are therefore rapidly being developed. Second-generation microalgal sys­tems have the advantage that they can produce a wide range of feedstocks for the production of biodiesel, bioethanol, biomethane, and biohydrogen. Biodiesel is cur­rently produced from oil synthesized by conventional fuel crops that harvest the Sun’s energy and store it as chemical energy. This presents a route for renewable and carbon-neutral fuel production. However, current supplies from oil crops and animal fats account for only approx. 0.3% of the current demand for transport fuels. Increasing biofuel production on arable land could have severe consequences for the global food supply. In contrast, producing biodiesel from algae is widely regarded as one of the most efficient ways of generating biofuels and also appears to repre­sent the only current renewable source of oil that could meet the global demand for transport fuels (Schenk et al. 2008).