Electrical engineering

Organic chemistry

Greenhouse gas

Hydrogen

Biodiesel

Agronomy

Biology

Biohydrogen

Biomass (ecology)

Engineering

Catalysis

Bioenergy

Hydrogen production

Chemistry

Renewable energy

Ecology

Environmental science

Renewable fuels

Biofuel

Waste management

Biochemistry

Fossil fuel

Biogas

Critical Reviews in Environmental Science and Technology

Fossil fuel continued overuse and carbon emissions issues have prompted increased research efforts on sustainable and renewable energy sources as alternative to fossil fuels. Biofuels include products derived from biomasses or their residues, such as: biogas, biodiesel, bioethanol, biomethanol, synthetic biofuels, biohydrogen and vegetable oil. Due to their properties, all of these may be used in conventional engines as produced, or blended with fossil fuels. First and second generation biofuels may be produced from a large variety of feedstocks, including food crops such as sugar beet, sugar cane, sorghum, energy-crops, such as lignocellulosic masses, and waste, like the organic fraction of municipal solid waste, or landfill leachate. In the last decade, a third generation of biofuels has emerged, i.e. those derived from microalgae. Even though their yield is higher, and their greenhouse gas footprint lower than previous generations', they still need large amounts of water and nutrients for production. In this paper, the most common biofuels (biogas, syngas, biodiesel, bioethanol and biobutanol) are reviewed and analyzed with particular attention on their carbon and water footprints and economic sustainability perspective.

Production technologies, current role, and future prospects of biofuels feedstocks: A state-of-the-art review