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Here's the Scoop: San Francisco to Turn Dog Poop Into Biofuel

Stefan Lovgren
for National Geographic News
March 21, 2006
 
Your house powered by pooch poop?

The idea may sound far-fetched, but officials in dog-friendly San Francisco, California, hope to harness the power of methane in doggie doo so it can be used for heating homes and generating electricity.

The technology of turning animal waste into energy was introduced in Europe some 20 years ago. It's practiced by hundreds of farms there, as well as by 16 U.S. dairy farms.

But San Francisco is believed to be the first U.S. city to explore the energy potential of pet waste.

In a pilot program to start this year, Norcal Waste, a garbage company that collects the city's trash, plans to use biodegradable bags and dog-waste carts to pick up the poop in one of San Francisco's most popular dog parks.

The waste will be run through a methane digester, a tank in which bacteria break down the feces to create methane. This biofuel can then be piped directly to a gas stove, heater, or anything else powered by natural gas.

"Scraping dog poop off your shoe, now that's something most people have been frustrated with for a long time," said Robert Reed, a Norcal spokesperson.

"Now we have an opportunity to turn this nuisance into something positive."

From Food Scraps to Dog Doo

Known for its green credentials, San Francisco already uses several recycling programs to divert almost two-thirds of its household garbage away from landfills. The city aims to divert all of its waste from landfills by 2020.

The poop-to-methane project is an extension of another bio-recycling program the city initiated ten years ago, when it began collecting food scraps from houses and restaurants and turning them into fertilizer for vineyards and organic farms.

Today 300 tons (272 metric tons) of food scraps are collected every day from more than 2,000 restaurants and tens of thousands of homes.

Norcal's Reed says that some of the more than a hundred farms in the area that have used the compost produced from food scraps have seen record yields.

"We have the most forward-thinking recycling program in the United States," he said.

The plan to recycle pet waste followed a recent study, which found that animal feces make up 3.8 percent of the garbage from residential collections in San Francisco.

"The city saw this percentage and said to us, We need to get down to zero [waste to landfills], so we want you to start thinking about how to collect the dog waste and what can be done with it,'" Reed said.

The high percentage is not surprising considering that San Francisco is home to an estimated 120,000 dogs, far more than there are children.

San Franciscans may be responsible about cleaning up after their dogs. But most of the droppings are wrapped in plastic bags and end up in landfills, where the waste may sit for generations.

If it's not picked up, animal waste may dissolve into the soil and flow into the groundwater.

Breaking It Down

Almost 10 million tons (9 million metric tons) of dog and cat waste is generated annually in the U.S., according to William Brinton, president of Woods End Laboratories in Mount Vernon, Maine. The lab specializes in analyzing compost and other waste.

"The amount of energy potential in dog and cat litter is higher than anything else because of the rich diet that we feed [pets]," said Brinton, who was consulted by Norcal to test the energy content of pet waste.

He estimates that 1 ton (0.9 metric ton) of animal waste could produce 50 gallons (190 liters) of diesel-equivalent fuel, enough to heat a house in New England for two weeks.

"Once you start multiplying it the numbers get pretty enormous, and all of a sudden it looks very appreciable," Brinton said. (Read Geographic magazine's "Powering the Future.")

The pet waste must be collected in special biodegradable bags before being placed into a methane digester, which works much like a compost bin.

Dog feces naturally contain bacteria called methanogens, which use hydrogen to break down carbon dioxide into microbial food. Methane gas is made as a byproduct of this process.

"It does not consume any energy to produce this energy, because you don't have to provide any energy to run the system," Brinton said.

The resulting biofuel can be piped into stoves, turbines, and other machines that run on natural gas.

"I see this effort as a logical next step of going after another portion of the organic waste stream that's currently going to disposal facilities," said John Majercak, a recycling expert at the Center for Ecological Technology in Northampton, Massachusetts.

"I think it's great that it's getting so much attention, and [I] hope that, after everyone has a chuckle over it, we are all that much more aware of the opportunity to rethink the way we handle our waste," he added.

The reaction from dog owners in San Francisco has been overwhelmingly positive, says Norcal's Reed. He expects to have special collection bins put up in Duboce Park, a popular San Francisco dog park, within a few months.

"Every day we get 20 to 30 people calling and asking about [the program] and how they can volunteer to make sure it's a success," he said.

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