Got milk? Convert it into biofuel

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.

Using table scraps from restaurants
To make any headway in replacing more polluting fuels, however, waste-devouring bioreactors would need to demonstrate their efficiency on a much larger scale, a challenge being taken up across the Pacific by researchers at the University of California at Davis.

Since October 2006, the university-led Biogas Energy Project has converted table scraps from some of the region’s top-tier restaurants, vegetable waste, grass clippings and cow manure into methane and hydrogen. The demonstration reactor processes between three and eight tons of the organic waste daily, according to Ruihong Zhang, a professor of biological and agricultural engineering. At that rate, the reactor’s daily output yields enough energy in the form of electricity to power up to 80 homes for a day.

There’s no shortage of starter fuel, with an estimated 5 million tons of food scraps dumped into California landfills every year. Once it’s had its fill, the multi-tank Davis reactor relies on a two-step anaerobic process in which hardy microbes turn the ingredients of, say, organic lemongrass tofu or endive salad into a less appetizing glop of acids and water. A second phase uses a separate bacteria mix to convert those acids into biogas.

If Onodera’s tack isn’t entirely new, Zhang said his use of spoiled milk has hit upon an “excellent” sugar and protein-rich environment for bacteria. Some dairy processing plants, in fact, have built digesters within their own facilities, though Zhang said the sizable reactors are designed to treat milk like wastewater and yield methane gas rather than hydrogen.

Like Onodera, Zhang said her process yields both gases, though the California project has arguably proved its mettle on a wider range of waste and on a much larger scale. “The conditions for treating different types of material can be different, but technically speaking, an anaerobic process can be used to convert anything that is biodegradable,” she said.

Building a commercial system
Zhang’s method is now licensed to Davis-based Onsite Power Systems, Inc., where she serves as the research and technology development director. With the prototype reactor as a guide, the company is building a commercial system that can handle up to 250 tons of waste per day. Within a year, Zhang said, the first unit could be ready for the City of Industry, a community west of Los Angeles that, as its name suggests, is overwhelmingly industrial. The reactor would consolidate and convert mostly food waste, but also some grass clippings and cheese processing leftovers. The biofuel, in turn, could power the city’s fleet of garbage trucks, offsetting the cost and power needed to transport the reactor’s raw materials.

“The reaction from the commercial businesses and even cities has been very positive,” Zhang said, noting that the technology offers not only biogas but also an environmentally-friendly way of reducing solid waste. “The leftover sludge will be processed into compost and also organic fertilizer,” she said. More surprisingly, the sludge’s undigested fibers could provide an excellent source of particle board.

In their own search for industrial-scale waste streams, researchers at the University of Birmingham in the United Kingdom found a willing partner in Cadbury Schweppes, of Creme Egg fame. A university spin-off called Biowaste2energy, or BW2E, has since taken the reins, with plans to build a mobile demonstration unit of its three-step system.

Like its counterpart in California, the BW2E method begins with a fermentation step that breaks foodstuffs down into organic acids, removing about 40 percent of the waste in the process, according to company CEO David Anthony. A purification step removes another 40 percent and a photobioreactor uses both light and bacteria to convert much of the remaining sludge to hydrogen, carbon dioxide and water. “I think where we fit into the niche is that we are reducing waste volume significantly more than what folks are doing by a single-step process,” Anthony said.

Beyond helping Cadbury cut down on a sea of caramel, BW2E is fielding calls from companies looking for better ways to dispose of fruit drink waste and spoiled fruit. All of which goes to show that where biogas is concerned, there’s no such thing as a bad apple.