University of Arizona (UA) researchers believe the microscopic organism algae will be providing fuel to power vehicles within the next five years.
Joel Cuello, UA professor of agricultural and biosystems engineering, said algae has been proven as a renewable source of fuels like ethanol, biodiesel, and hydrogen, and his research team is working on ways to make such algae biofuels cheaper and commercially feasible.
"I really believe we will be able to make use of algae-based biofuels, probably in two to three years," Cuello said. "We will have the right mix of technologies in place in two to three years, and it will be at the pump, I would say, in five years."
Different types of algae – with different qualities and attributes – are grown in Cuello's lab in UA's Shantz Building. Some algae varieties produce fatty acids that can be converted to biodiesel, others produce starches that can be converted to bioethanol, and some types of algae directly produce hydrogen gas, he said.
Algae offers major advantages over other things grown as sources for renewable energy, Cuello said.
Growing algae produces oxygen and takes carbon dioxide out of the environment. It grows more productively than other fast-growing energy crops while requiring less space. Non-potable and treated wastewater can be used for growing algae. And using algae for fuel production does not take food out of the mouths of people or animals, he said.
The process begins with selecting the algae species appropriate to produce the desired fuel. Species and strain selection also considers the quickest and most productive type of algae, he said.
Huge amounts of algae are needed for large-scale biofuel production. Mass production takes two forms: growing it in open ponds or more complex and costly closed photobioreactors.
Open ponds where nutrients flow along a racetrack-like circuit offer a simpler and less expensive way to produce algae, but must deal with fluctuations in temperature and solar radiation as well as potential contamination.
Photobioreacators, which are large containers in which algae is grown, control the environmental parameters and ensure the best environment for algae growth, but are generally more costly, he said.
A new less expensive, more efficient design of photobioreactor has come out of Cuello's UA lab.
"It's called the Accordion because it is suggestive of the geometry or configuration of the musical instrument. It is a vertical series of flat plate reactors at different angles, and the algae and nutrient solution is circulated through those flat plates," Cuello said.
Unlike other photobioreactors, Accordion is made of inexpensive, flexible plastic to keep costs down, Cuello said. The system is also modular and scalable for high-volume production in an economically feasible manner, he said.
After production the algae must be harvested.
"Harvesting is not easy. We are dealing with microalgae, which are microscopic. And they are floating around in water, so it is not so easy to separate them from the liquid nutrient solution in which they are suspended," Cuello said.
Centrifuges are most commonly used to separate out the valuable algae, a process that is very energy intensive.
"We are looking at developing new methods or approaches for accomplishing harvesting microalgae from liquid nutrient solutions," he said.
UA has received a provisional patent for Accordion, and is in negotiations with a Norwegian company interested in a licensing option or agreement to use the device commercially, Cuello said.
The next step is dewatering, or drying, the harvested algae. The Southwest, with its abundant sunshine and high temperatures, is an ideal area for drying the algae biomass, he said.
After drying, the oils are extracted or starch is separated to produce biodiesel or bioethanol.
Kuwahara is studying how best to use wastewater to effectively produce algae. This saves valuable groundwater for other purposes, and actually cleans the wastewater during the process of growing the algae, she said.
The process also produces oxygen while removing carbon dioxide from the environment, she said.
"We hope to make it a zero impact growing process," Kuwahara said.
Cuello said that with some addition of nitrogen and phosphorus, wastewater grows algae as well as more expensive solutions designed specifically for that purpose.
Takanori Hoshino, a biosystems engineering graduate student, is investigating better ways to produce hydrogen gas from algae.
Hydrogen can be used to power vehicles. But now, 95 percent of hydrogen is produced from natural gas, a fossil fuel, he said.
Hoshino is working with Chlamydonomas reinhardtii, a type of algae, to produce more hydrogen gas from a given volume of algae.
Algae is not the only UA focus of research for biofuel sources.
Mark Riley, UA agricultural and biosystems engineering department head, said a project using arid lands to grow sweet sorghum for ethanol is close to commercialization.
Sweet sorghum grows quickly – up to 4 meters in four months – and is suited to Arizona because it is salt tolerant and can use reclaimed wastewater for irrigation, Riley said.
Sweet sorghum can be fermented directly into ethanol, and Riley said a Pinal Energy LLC plant near Maricopa, Ariz., is nearing commercialization of the first large-scale energy crop for the Southwest.