All told, agriculture, forestry, and municipal waste produces around 900 million metric tons of possible biofuel feedstock a year. But the researchers estimated only 223 to 225 million metric tons — about a quarter — can be diverted to biofuel use in ways that don’t ultimately add to greenhouse gas emissions. At the current rates at which biomass can be converted into biofuel, that would supply as much as 16 percent of the European Union’s road transportation needs by 2030. (Though in reality, the heating and electricity generating sectors would be competing to use the biofuel as well.) Road transportation is one of the few sectors of the European economy where carbon emissions have risen rapidly in recent years — it’s on track to become the EU’s biggest source of emissions by 2030.
The study considered three different methodologies for turning biomass into fuel: biochemical ethanol, which uses enzymes to break the cellulose down into simple sugars and then converts them into ethanol; FT-diesel, which gasifies the feedstocks and then converts them into diesel or gasoline; and pyrolysis, an alternative form of gasification. It then looked at various wastes — wheat straw from farming, slash residue from forestry, sawdust from the timber industry, and municipal solid waste (MSW) — and found they all avoided anywhere from 60 to almost 300 percent of fossil fuels’ greenhouse gas emissions.
The advantage of making these sorts of cellulosic and advanced biofuels from waste material is two-fold. One, the biofuels don’t compete with food crops and thus don’t drive up food prices. Two, by relying on waste, they don’t really increase demand for agriculture and other economic activities that drive up carbon emissions.
Another advantage of the study was it looked at the full life cycle and trade-offs involved in using these feedstocks. For example, some forestry residue needs to be left behind, because it returns nutrients to the soil and sustains future forestry growth. And in many climates, the residue decomposes slowly enough to act as a carbon sink. As a result, the researchers concluded that no more than 50 percent of forestry waste should be diverted to biofuel use, in order to maximize the amount of carbon that’s kept out of the atmosphere.
Waste from agriculture is susceptible to much of the same logic, since nutrients need to be returned to the soil to avoid reliance on fertilizers, and because much of the waste is already put to alternative uses.
Much of municipal solid waste is already recycled in Europe, and the researchers concluded the recycling was more valuable than the waste’s raw energy content. But that still leaves around 6 million metric tons of available wood waste per year, and 44 million metric tons of cellulosic household waste. Importantly, converting municipal waste into biofuel avoids dumping it in landfills, which produces methane — a potent greenhouse gas — as the waste decomposes. That’s why use of MSW for biofuel avoids such a huge amount of greenhouse gas emissions.
Account for all those limits, and you arrive at the study’s estimation that about a quarter of the EUs’ annual waste can be used sustainably for biofuel production.
Source: Climate Progress. Reproduced with permission.