As aircraft are bound to a liquid fuel (it has the most energy content per weight) alternative resources need to be converted into liquid fuels. The industry needs to consider which source is the best for biofuel, it needs to be relatively easy to 'harvest' compared to fossil fuel, with no impact on human food or water supply whatsoever and must be environmentally friendly.
Aircraft engines still cannot run on water but, indirectly, this water can be and is a source of algae. And these algae have a high yield compared to other biomass sources which makes them very interesting to the energy industry. A big advantage of many biofuels over 'normal' fuel types is that they are biodegradable, and if spilled, are harmless to the environment.
Sources for alternative fuel investigated by the industry.
Excerpt from the document:
Although the industry and investors flirted with alternative fuels in the late 20th century, only recently has research and development flocked towards these innovations. Engine, airframe and fuels manufacturers march onward alongside venture capitalists, automotive companies and the energy sector. Some invest in known processes like Fischer-Tropsch, while others develop new ways to convert hydrocarbons into drop-in petroleum replacements that must also fit flawlessly into pipelines and the delivery infrastructure.
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