Got milk? Convert it into biofuel

Bryn Nelson Columnist

There’s no use crying over spilled milk in Japan. Not when it can be converted into biogas.

As the alternative energy movement picks up steam, researchers are increasingly looking to their local communities for tons of organic waste that could be transformed into more environmentally friendly biofuels. At the Nigata Institute of Technology in Kashiwazaki, Japan, that mindset has spurred scientists to give new life to spoiled milk and rotting jellyfish. At the University of California at Davis, engineers have repurposed table scraps from swank Bay Area restaurants. And at the United Kingdom’s University of Birmingham, researchers have diverted gooey nougat, caramel and other confectionary waste from the nearby Cadbury Schweppes plant.

Who knew that Cadbury Creme Eggs could be good for the environment?

Food crops such as corn and sugarcane have been tapped as major sources of energy production around the world, especially for distilling ethanol. Amid growing concerns of potential food-or-fuel competitions, other companies are tinkering with oils made from flowering plants and algae or hoping to exploit the energy-rich biomass of fast-growing switchgrass to create biofuel. With mountains of discarded food slated for landfills or incinerators, however, researchers also are discovering that a little ingenuity can turn the world's abundant garbage into a whole lot of power.

A new report by the Pacific Northwest National Laboratory in Richland, Wash., in fact, suggests that garbage could play a big role in helping the Pacific Northwest produce up to 15 percent of its own biofuel from locally available resources. In particular, waste-derived biogases such as hydrogen and methane can be fed into turbines to generate electricity and heat, compressed to power fuel cells, or concentrated into a form of natural gas. Methane is among the "greenhouse gases" blamed for global warming, though when burned it releases significantly less carbon dioxide — the main warming culprit — than other fossil fuels such as coal and oil.  
 
Alternatives to fossil fuels
Masayuki Onodera, an associate professor of applied chemistry and biotechnology at Nigata Institute of Technology, said hydrogen gas is gaining popularity as a fossil fuel alternative. “But how do we get hydrogen economically? It’s one of the problems.”

Serendipitously, as Onodera explained during a presentation at last month’s annual conference of the American Association for the Advancement of Science, Japan has been plagued recently by an abundance of discarded milk. Exactly why isn’t clear; perhaps schoolchildren prefer sodas, Onodera suggested. (Not him, however: “When I was in elementary school, I drank much milk,” he said with a smile.)

With a friend whose company transports spoiled milk to a local incinerator, Onodera hit upon the idea of diverting the cargo and putting some of the curdled cow juice to good use.

The professor and his colleagues began their two-step conversion process by brewing a batch of sugar-spiked solution mimicking the bacteria-friendly confines of wastewater. Their small bioreactor relied on heat-loving microbes to digest the sludge in the absence of oxygen at a toasty 131 degrees Fahrenheit, approximating the conditions within some landfills and creating methane as well as carbon dioxide (scientists consider the carbon dioxide release “carbon-neutral” because its escape into the atmosphere is balanced by what had been taken in during photosynthesis by the grass or corn that fed the dairy cows).

Onodera’s team added a portion of the digested glop to a second container filled with rancid milk. When the solution was starved of oxygen and kept at a relatively neutral pH, it yielded eight times its own volume in biogas over a one-week period. Half the captured biogas was hydrogen, the other half carbon dioxide. By periodically replacing part of the bacteria-laden sludge with milk and making sure the solution remained at the right pH, Onodera found that the system continuously produced biogas until he stopped it 100 days later. By then, the solution was yielding more than five times its own volume in biogas every two days.

Using the same technology, Onodera hopes to harness the power of other school lunch castaways, whether pushed-aside carrots, detested peas, or his own son’s nemesis, the tomato. The nearby presence of one of the world’s largest nuclear power plants has presented another unexpected bounty that might be similarly harvested: jellyfish.

Like many other coastal installations, the Kashiwazaki-Kariwa Nuclear Power Plant uses seawater as a coolant. “Sometimes, many jellyfish come near the power plant,” Onodera said — an ill-advised foray, especially when they become stuck en masse in the cooling system. “In summertime, the jellyfish are producing a bad smell,” he said. One creative solution suggested by his bioreactor would use the power of bacteria to turn the gelatinous muck into methane, a potential boon for the surprising number of nuclear power plants around the world with similar jellyfish-induced headaches.

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