http://biomassmagazine.com/articles/16380/converting-waste-to-biofuels-reduces-emissions/
[links in online article]
Study shows how US can maximize benefits of waste-derived fuels
By Allison Bell, UCLA | August 08, 2019
The United States could produce enough energy each year by harnessing
waste—from landfill refuse to cow manure—to power the states of Oregon
and Washington, all while cutting the equivalent of 37 million cars’
worth of carbon.
That’s according to research published in Nature Energy from UCLA
industrial ecologist and energy economist Deepak Rajagopal and urban
planning doctoral candidate Bo Liu.
“The benefit of using waste is that we are generating waste anyway. It
is a leftover resource that we have not conventionally thought about,”
Liu said.
The types of waste examined in the paper fit under the umbrella of
bioenergy—renewable resources that are obtained from converting plant
and animal material into electricity, biofuels or heat. While the U.S.
doesn’t produce energy from waste on a large scale, Liu said, the
processes for obtaining energy from organic materials are well
established. European waste-to-energy plants, for example, processed 106
million tons of waste in 2017, according to the Confederation of
European Waste-to-Energy Plants.
Biofuel is one type of bioenergy that is widely produced in the
U.S.—almost all of it coming from agricultural crops. In 2011, 96
percent of the ethanol produced in the U.S. came from corn, according to
the Biomass Energy Data Book.
Policymakers and business interests have promoted biofuels from crops
for decades. In 2005, Congress passed standards that require
incorporation of renewable fuels in gasoline and other transportation
fuels. The U.S. also spent billions of taxpayer dollars subsidizing
ethanol over the past 35 years.
But crop-based ethanol creates other problems—including increased food
prices and environmental damage from expanding agriculture, such as
habitat destruction, fertilizer runoff and water use. These effects have
led some experts to call for reducing its use.
“The U.S. has tried biofuels, and they are important because we need
more renewables, but we need better biofuels,” Rajagopal said.
Using waste as a source instead could prove a sustainable alternative
for future industry growth. However, not all waste biofuels are created
equal. Benefits vary depending on what kind of waste is used, how it
gets processed, what the end products are and where they’re produced.
Rajagopal and Liu examined this variability by conducting life cycle
analyses, or examinations of products from creation to end of life, of
four types of waste: agricultural, forestry, landfill and cow manure.
The study encompassed 15 energy conversion technologies and 29 waste
types. In their analysis, the researchers combined existing data from
the literature on waste conversion technologies with local waste
availability from base-year estimates and electricity portfolios to
determine relative energy gains and emissions reductions.
Because burning of bioenergy products themselves produces greenhouse gas
emissions, the ability of bioenergy to reduce overall greenhouse gases
is tied to the energy replaced, making local context important. The
greenhouse gas savings from use of bioenergy to produce electricity, for
instance, would be greater in areas where electricity comes from
carbon-based fuels like coal, as opposed to areas that generate a lot of
solar and wind power.
Overall, the study found that the U.S. has the potential to generate 3.1
to 3.8 exajoules (a measure of energy) of renewable energy each year
using available waste resources. By comparison, the entire states of
Washington and Oregon consumed about 3.3 exajoules of energy in 2017,
according to the Energy Information Agency. The study also concluded
that using waste products has the potential to displace 103 to 178
million metric tons of carbon dioxide emissions—an amount equivalent to
taking 37 million passenger vehicles off the road based on typical
passenger vehicle emissions of 4.6 metric tons of carbon dioxide each year.
A key finding was that no one method of bioenergy production maximizes
net energy gain, renewable energy gain and climate benefits. Some create
more renewable energy, but require more energy to do so, resulting in
less overall greenhouse gas emissions savings. Thus, identifying the
optimal bioenergy application in any situation depends on the intended
outcome.
Policies based purely on meeting renewable energy targets, such as
Congress’s requirement of biofuels at gas pumps, may not produce optimal
results, the study found. Instead, Rajagopal said, policymakers should
work to clarify interests. Maximizing use of renewables may promote
energy independence, but cutting the maximum amount of greenhouse gas
emissions is a more effective way to counter climate change, he said.
Biofuels should not be limited to any one application, with potential
transportation applications ranging from cars and trucks to planes and
ships, Rajagopal said. Diversification is key.
Other forms of renewable energy, such as solar and wind, provide choices
for electricity generation, but large-scale transportation sectors will
still need burnable fuels for the foreseeable future.
Airlines have already begun to explore biofuel alternatives. In 2016,
United Airlines and jet fuel company AltAir spearheaded commercial
deployment of waste biofuels for aviation, using a mix of alternative
jet and conventional fuels.
Studies have found that aviation, shipping and trucking account for
about 8% of carbon emissions globally. In these industries, Rajagopal
said, a simple mandate requiring biofuel integration into fuel mixes
could be effective because it would encourage further development of
large-scale biofuel technologies.
“In all these applications electric vehicle technology is still not
there. Electric batteries are still not there,” Rajagopal said. “So we
still need alternatives to oil. I think there is a role there for
biofuels if you do it right.”
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