Next-generation biofuels, such as cellulosic bioethanol, biomethane from waste, synthetic biofuels obtained via gasification of biomass, biohydrogen, and others, are currently at the center of the attention of technologists and policy makers in search of the more sustainable biofuel of tomorrow. To set realistic targets for future biofuel options, it is important to assess their sustainability according to technical, economical, and environmental measures. With this aim, the review presents a comprehensive overview of the chemistry basis and of the technology related aspects of next generation biofuel production, as well as it addresses related economic issues and environmental implications. Opportunities and limits are discussed in terms of technical applicability of existing and emerging technology options to bio-waste feedstock, and further development forecasts are made based on the existing social-economic and market situation, feedstock potentials, and other global aspects. As the latter ones are concerned, the emphasis is placed on the opportunities and challenges of developing countries in adoption of this new industry.

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The global demand for energy, particularly for transport fuels, will continue to increase significantly in the future. In addition to other options, like increased technological efficiencies, traffic reduction or modal shift, biofuels are promoted to contribute strongly to the transport sector in the years to come. Biofuels are also promoted as part of the EU strategy for decarbonising the transport sector with the aim of reducing associated GHG emissions. This paper considers some of the most important biofuels. A selection of biofuel options (biodiesel, bioethanol, biomethane, hydrotreated vegetable oils and fats, lignocellulosic-based fuels) were characterised by their conversion technologies and stage of development. They were analysed, concerning technical (overall efficiency), economic (investments and biofuel production costs) and environmental aspects (GHG performance). Additionally, GHG mitigation costs were calculated with regard to the GHG-based biofuel quota.

One of the future-generation biofuel options that has recently recieved increased attention is the production of biofuels from microalgae. Besides the use of algae oil for physicochemical biodiesel production, biochemical and thermochemical pathways are possible. Although there is still a need to research algae production systems, downstream processing (e.g., biofuel production) needs to be researched in parallel. As there are several methods to produce biofuel from algae, different possible production processes are reviewed. By investigating the different steps of each of the processes and highlighting the challenges and risks that can occur, it is possible to make a decision regarding which pathway might be feasible for algal resources in the future.

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