5.1 Introduction

The world has been confronted with an energy crisis due to the depletion of finite fossil fuel resources. The use of fossil fuels as energy is now widely accepted as unsustainable due to depleting resources and also due to the accumulation of green­house gases in the atmosphere.

Biomass provides a number of local environmental gains. Biomass resources in­clude agricultural and forest residues, algae and grasses, animal manure, organic wastes, and biomaterials. Supply of these resources is dominated by traditional biomass used for cooking and heating, especially in rural areas of developing coun­tries. Biomass mainly now represents only 3% of primary energy consumption in industrialized countries. However, much of the rural population in developing coun­tries, which represents about 50% of the world’s population, is reliant on biomass, mainly in the form of wood, for fuel.

Energy forestry crops have a much greater diversity of wildlife and flora than the alternative land use, which is arable or pasture land. In industrialized countries, it is expected that the main biomass processes utilized in the future will be direct com­bustion of residues and wastes for electricity generation, bioethanol and biodiesel as liquid fuels, and combined heat and power production from energy crops. The future of biomass electricity generation lies in biomass-integrated gasification/gas turbine technology, which offers high energy-conversion efficiencies. In the future, biomass will have the potential to provide a cost-effective and sustainable supply of energy, while at the same time aiding countries in meeting their greenhouse-gas-reduction targets. By the year 2050, it is estimated that 90% of the world’s population will live in developing countries.

Prior to the establishment of the US Department of Energy’s (DOE) Aquatic Species Program, very little work had been conducted on biofuel production from lipid-accumulating algae. While the general idea of using algae for energy produc­tion has been around for over 50 years (Meier 1955), the concept of using lipids derived from algal cells to produce liquid fuels arose more recently. The research of liquid fuel produced from microalgae was begun in the mid-1980s in 20 centuries

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

(Xu et al. 2006). Aquatic biomass may represent a convenient solution because it has a higher growth rate than terrestrial plants. Microalgae have been extensively studied so far, as they can grow in both fresh — and saltwater environments. Algal biomass contains three main components: carbohydrates, proteins, and natural oils. Algae are a promising source of renewable energy.

Microalgae can potentially be employed for the production of biofuels in an eco­nomically effective and environmentally sustainable manner. Microalgae have been investigated for the production of a number of different biofuels including biodiesel, bio-oil, biosyngas, and biohydrogen. The production of these biofuels can be cou­pled with flue gas CO2 mitigation, wastewater treatment, and the production of high — value chemicals. Developments in microalgal cultivation and downstream process­ing are expected to further enhance the cost effectiveness of biofuel from microalgae (Li etal. 2008).

Algae, like corn, soybeans, sugar cane, Jatropha, 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 plant oil can be converted into bio­diesel; hence biodiesel is a form of solar energy. 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.

Algae for biofuels have been studied for many years for the production of hy­drogen, methane, vegetable oils (for biodiesel), hydrocarbons, and ethanol. Algal hydrogen production has been extensively researched for over three decades, but no mechanism for it has ever been demonstrated.

Algae can be used to produce biofuel, called algae fuel, algal fuel, or even third- generation biofuel. Compared with second-generation biofuels, algal fuels have a higher yield: they can produce 30 to 100 times more energy per hectare compared to terrestrial crops.

The advantages and disadvantages of biofuel production using microalgae are shown in Table 5.1. Among the advantages are that the high growth rate of microal­gae makes it possible to satisfy massive demand on biofuels using limited land re­sources without causing potential biomass deficit, microalgal cultivation consumes less water than land crops, the tolerance of microalgae to high CO2 content in gas streams allows high-efficiency CO2 mitigation, microalgal farming could be poten­tially more cost effective than conventional farming, and nitrous oxide release could be minimized when microalgae are used for biofuel production.

On the other hand, one of the major disadvantages of microalgae for biofuel pro­duction is the low biomass concentration in a microalgal culture due to the limited light penetration, which in combination with the small size of algal cells makes the harvest of algal biomasses relatively costly. The higher capital costs and the rather intensive care required by a microalgal farming facility compared to a conventional agricultural farm is another factor that impedes the commercial implementation of the biofuels-from-microalgae strategy.