Scientists and engineers at the University of Arizona are on a mission to develop sustainable agricultural biofuel field crops for Arizona and the desert Southwest – crops that will fuel a new industry as well as America's engines.
Biofuels – fuels developed from biomass such as sugar or grain crops or algae – have as many and diverse uses as traditional energy sources and could be used more widely in the future to power many technologies including automobiles, homes, industrial manufacturing facilities and airplane engines.
"There's no doubt that we're going to have biofuels in the future because no matter what, petroleum is a finite resource," said Dennis Ray, a plant geneticist at the College of Agriculture and Life Sciences. "Problems today are not solved by one discipline."
The biofuel development project could benefit Arizona's economy as well as the environment.
"We're looking at rural development. If you have a little industry in this area, you need people to run the processing plant. That means jobs. That means bringing money back into these communities," said Ray. "It's always a much bigger picture for what we're looking at in the long run."
An ideal place for biofuels
Arizona could be home to a thriving biofuel industry in the future, said Mark Riley, professor and department head of agricultural and biosystems engineering.
"We get a tremendous amount of sunlight," said Riley, which enables crops to be grown year-round or off-sequence from other parts of the country.
"A good example is from traditional agriculture. Yuma County in the western part of the state grows 95 percent of the country's winter vegetables because nowhere else can grow vegetables during that time of the year. In that same vein, we could be growing sources of sugar to make ethanol off-sequence from when other regions are growing corn."
"Biofuels don't make sense if you have to transport them long distances," said Riley. "Some of the largest population growth in this country is in the Southwest, and there really isn't yet a whole lot of agriculture geared toward producing fuels."
"We need to be producing the fuels close to where they're going to be used."
Petroleum is transported through an extensive network of pipelines from the Gulf of Mexico and the Eastern Seaboard. The pipes are not completely watertight, so the greater the transport distance, the more water leaks in. This works because petroleum does not mix with water, but ethanol does.
Ethanol, therefore, needs to be transported by truck, so producing it locally would save on fuel and transportation costs.
Sugarcane of the desert
To be a viable biofuel crop for Arizona, the plants need to do well in arid environments. That rules out corn, which requires a lot of water, as an option in most parts of the Southwest.
"There are hundreds of plants that you could use as biofuels," said Ray. "Oil seeds where you can use the oil almost directly for diesel, cellulosic plants where you can break down cell walls into ethanol, and plants like sorghum where you use the sugar to make ethanol."
"I'm a plant breeder geneticist, so what I do is improve or change the plants for whatever's needed," said Ray. "I work on three very different crops. One is lesquerella, which is an oil seed. Another is guayule, a rubber-producing plant that also makes these amazing resins, and these resins can be burned directly or used in all sorts of different ways as a fuel source. And then of course there's sweet sorghum."
Called the sugarcane of the desert, sweet sorghum is one of the most promising crops for biofuel.
"Sweet sorghum is a tall grass, and it grows to about 3-4 meters," said Riley. "It can grow in about 110-120 days, and it produces a substantial amount of ethanol. We think we can get 500-600 gallons of ethanol per acre – generally for corn you get about 300 gallons of ethanol per acre."
Sweet sorghum also is easier to process into fuel than corn.
Ethanol is produced from corn and other grain crops in basically two steps: First the starch is broken down into sugars, and then the sugars are fermented into ethanol by yeast, just as beer is fermented.
When juiced, crops such as sugarcane and sweet sorghum yield sugars instead of starch, thus eliminating the first steps of the process for corn-based ethanol.
"Even after you squeeze the stalks and get the juice out, there's a lot of biomass that's still available," said Riley. "That could be used as animal feed as a way to supplement what a grower would be able to get."
Don Slack, a professor in the department of agricultural and biosystems engineering, has studied the irrigation needs of sweet sorghum. "It's known as a drought-tolerant, salt-tolerant, tough crop," said Slack. "Sorghum would be a preferred crop in a hot, arid region."
Sweet sorghum needs little water, and since it's not intended for food it can be irrigated with treated wastewater, which provides many of the nutrients the crop needs.
It also has very low nitrogen requirements, according to a study by Mike Ottman, an agronomist in the plant sciences department.
Said Ottman: "You wouldn't think about it but nitrogen fertilizer is made using fossil fuels. In the case of corn, maybe one-third to half of the energy that goes into growing the crop is the energy required to make the fertilizer."
"Sweet sorghum's not part of the food chain, so if there's more sweet sorghum that's going toward producing biofuels it's not taking away corn that's used to feed animals or people," added Riley.
The researchers are trying to develop a way to plant and harvest effectively two crops in one year.
"You could effectively double the growth, double the amount of ethanol per year, just because our growing seasons are much longer than other parts of the country," said Riley. "It's really taking advantage of our location."
Search for sustainability
The scientists are testing and developing several other crops, including three types of switchgrass and three varieties of perennial grasses in the genus Panicum.
These grasses produce cellulose instead of starch. Like starch, cellulose is made up of chains of sugar molecules held together by what are called glycosidic bonds. However, the orientation of the bonds in a cellulose molecule creates a more rigid structure, making cellulose harder to break down.
"The conversion of cellulose to sugar is a little more difficult than the conversion of starch to sugar," said Ottman. "You can't just do straight chemical hydrolysis. You need enzymes, and these enzymes are expensive."
For now, most of the ethanol production plants in the U.S. process grain crops. But that could change: The cellulosic process should start taking off by 2015, according to the target date of our energy policy, said Ottman.
And perennial grasses as biofuel crops have important benefits. Cellulose is one of the most abundant organic molecules on Earth and could yield an equally abundant source of fuel on the future.
Numerous research questions remain for each crop, including the amount of water and fertilizers needed, when to plant and when to harvest, how far apart to plant the seeds to optimize the harvest and how best to store and transport the fuel once it's processed. Said Ray: "These are all little things that make a big difference."
"The goal of the project, of all these projects, is to have a commercial product," said Ray. "The end goal is to give back to folks who have given to us through funding and in other ways."
The agricultural methods developed in Arizona would work in many arid or semi-arid environments, said Ray, "which actually applies to much of the Earth. So what we do here is transferrable. The desert plants don't know if they're in Chihuahua or Texas. Borders mean nothing to them. It has to do with the environment."
"One hundred and fifty years ago petroleum was used for kerosene for lamps in the Northeast to replace whale oil. In 150 years you wouldn't recognize what we're doing with biofuels now," said Ray. "We're gaining knowledge so that we understand what's needed and how this whole process works."
Biofuels research at the UA is funded by the U.S. Department of Agriculture's Agricultural Research Service, the U.S. Department of Transportation, the Sun Grant Initiative from the U.S. Department of Energy and the UA's College of Agriculture and Life Sciences.