密歇根新闻广播 抑制藻类生物燃料（在线收听）

For years, scientists have been developing ways to put algae in your gas tank. It works, but we're still a long way from buying algal biofuel at the pump.

Researchers at the University of Michigan have been experimenting with methods that could improve the fuel's long-term prospects.

In 2016, the team set up 80 large containers at a site near Pinckney, northwest of Ann Arbor, to serve as small ponds where they could grow different species of algae together. Picture a field surrounded by trees with row after row of round, black tubs filled with bright green liquids, like witches cauldrons. U of M recently released their findings.

Bradley Cardinale is a professor in U of M's School for Environment and Sustainability. He oversaw the research team. Cardinale says algae have molecules that are highly combustible.

"Things like fatty acids, polysaccharides and carbohydrates are things that we can burn easily and get a lot of energy out," he said in an interview with Michigan Radio Morning Edition host Doug Tribou. "The second thing that makes them viable is that they don't require a lot of area. We can grow a lot of algae in a relatively small area of pond that would not require a huge ecological footprint in the way that something like corn ethanol might."

Grow, grow, grow

The challenge is to grow algae at a large enough scale to generate a steady output that can be sent to a refinery.

"You need to get high yields out of the algae, so we need to have a high mass of the crop that needs to [have] good molecules for combustion like these fatty acids," Cardinale said. "It needs to be resistant to pests and disease. It needs to be stable in the face of weather fronts that Mother Nature is going to throw at you."

The U of M researchers tried to grow different species together, using an approach called ecological engineering, or biomimicry.

"One of the very first principles of ecological engineering is that no single species can be good at everything, but you can potentially take several different species, each of which is good at a different thing, and grow them in combinations and have them collectively accomplish all of the things you need," Cardinale said.

Commercial interests

Exxon Mobil has taken a different approach in its work on algal biofuel. According a recent report by Fast Company, the oil company and its partner, Synthetic Genomics, believe they will be able to produce 10,000 barrels of algal biofuel a day by the year 2025.

As Fast Company noted, "by tweaking a particular gene in a certain species of algae, they were able to make the algae produce twice as much fat as it would in the wild, but still grow as quickly as usual. That fat can be made into fuel."

But Cardinale says he's skeptical of their technique.

"We can, in fact, genetically engineer species in the lab that produce high yields that also give us these great biomolecules like fatty acids, but those fatty acids are very yummy to things that like to eat algae in nature," he said.

Growing massive amounts of algae requires space and that means outdoor ponds that are up to an acre in size. Outside the safety of the lab, Cardinale believes Exxon Mobil will see different results.

"In an open cultivation pond, they're going to have population crashes and it's going to be very difficult to sustain those genetically engineered species at the scale of open commercial ponds."

Cardinale says U of M might partner with energy companies to develop its own commercially viable outdoor ponds. He and his fellow researchers also hope to discover more kinds of algae that can be paired up.

"Our analyses suggest there are probably hundreds of thousands of combinations of species that occur naturally that are even better than the ones that we've identified and worked with so far."

Environmental upsides ... and downsides

Algal biofuel is carbon neutral. When burned, it releases the same amount of carbon the plants took up while they grew.

However, Cardinale notes that it would take massive amounts of fertilizer to grow algae at commercial scale. Fertilizers are the biggest source of water pollution worldwide.

A long way to go

Don't expect to see "algal biofuel" next to unleaded regular and diesel at your local filling station anytime soon.

Cardinale said. "If the oil prices remain low, or we have an administration that does not prioritize renewable fuels, we're on the timescale of probably several decades."