Most transportation be it personal or commercial depends on liquid fuels. The availability of liquid fossil fuels is decreasing and the cost is rising, Our dependence on these transportation fuels will continue until batteries and the electrical grid are greatly improved.
The only current alternative to fossil fuel is biofuel, ethanol from corn and biodiesel from soy beans. Ethanol makes up a scant two percent of our liquid fuel needs, biodiesel less than that. The figure is even lower than that when you account for the fossil fuel energy inputs to the production of biofuels. We won’t see row crop biofuels making up a larger share of our fuel needs because of the negative environmental impacts and the fact that biofuels production drives up food prices.
Another source of biofuel could be to waste to fuel plants. There are already plants which burn garbage (solid waste) for the generation of electricity, consuming about fifteen percent of all solid waste. Although this does produce energy and reduce the need for landfills, it doesn’t help with transportation needs. There are also concerns about the environmental and health impacts of the combustion products.
Liquid fuels such as methanol and ethanol can be produced from solid waste but currently the process is less efficient and more costly. Solid waste consists mainly of cellulose from various plant products and fossil fuel derived items like tires and plastic. Other unexploited sources of feedstocks are agricultural wastes from farming and timber harvesting. Even grass clippings and leaves could be utilized.
These materials when heated to high temperatures produce a mixture of gasses. The gasses can be chemically manipulated with catalysts and turned into methanol. Another methodology utilizes just the cellulose component. The materials are treated with sulfuric acid to release the sugar which is then fermented by traditional methods to produce ethanol. Japan is currently using this technology to produce ethanol for blending with gasoline.
A model system for waste to fuel would look something like a plant sited near a current landfill. Municipal solid waste, agricultural wastes, and suburban wastes would all be brought to the processing plant where the materials would be separated . Materials which are unusable wold still be land filled. Process heat for the plant would be provided to a degree by burning methane captured from the landfill.
So how much fuel can we expect to get? Estimates vary wildly. How much useful waste can be collected, how much energy will be consumed in the process, and the efficiency of the conversion process are just some of the confounding variables. Estimates range from a few percent up to as much as thirty percent of our liquid fuel needs.
The biggest problem with waste to fuel strategies is the resource base. The best way to contain the rising cost of any and all fuels is to become more efficient. The easiest way to be more efficient is to reduce waste. That means a diminishing resource base. This may not be a business model that many will wish to pursue.
The only long term solution to our energy needs, regardless source or form is to use a lot less and produce what we need sustainably. We have to learn to live within our means.