SAN FRANCISCO, California (AP) -- City officials are hoping to harness the power of dog waste in this dog-friendly city where animal feces make up nearly 4 percent of residential waste.
San Franciscans already recycle more than 60 percent of their garbage, but officials hope to turn into energy the 6,500 tons (5,897 metric tons) of dog waste a year -- nearly as much as disposable diapers, according to the city.
Within the next few months, Norcal Waste, a garbage hauling company that collects San Francisco's trash, will begin a pilot program under which it will use biodegradable bags and dog-waste carts to pick up droppings at a popular dog park.
The droppings will be tossed into a contraption called a methane digester, which is basically a tank in which bacteria feed on feces for weeks to create methane gas.
The methane could then be piped directly to a gas stove, heater, turbine or anything else powered by natural gas. It can also be used to generate electricity.
Methane digesters are nothing new. The technology was introduced in Europe about 20 years ago, and more than 600 farm-based digesters are in operation there. Nine are in use on California dairy farms, and chicken and hog farms elsewhere in the United States also use them.
Neither Norcal Waste spokesman Robert Reed nor Will Brinton, a Maine-based recycling and composting consultant, knew of anyone in the United States who is using the $1 million (euro840,000) devices to convert pet waste to energy. But Brinton said some European countries process dog droppings along with food and yard waste.
"The main impediment is probably getting communities around the country the courage to collect it, to give value to something we'd rather not talk about," Brinton said. "San Francisco is probably the king of pet cities. This could be very important to them."
San Francisco -- the city named after Saint Francis, patron saint of animals -- has an estimated 240,000 dogs and cats.
Some experts believe methane digestion must become more attractive economically before it gets popular. Landfill space is relatively cheap, and natural gas and electricity also remain fairly inexpensive.
Reed points to San Francisco's groundbreaking food composting program, which began 10 years ago, as proof an unusual idea can work in this forward-thinking city. A Norcal Waste subsidiary collects 300 tons (272 metric tons) of food scraps per day from homes and restaurants and converts it into a rich fertilizer sold to vineyards and organic farms.
"Now, the city's asked us to look at dog waste specifically," Reed said.
Because animal waste contains disease causing germs, composting it at home with yard waste and food scraps can be unsafe.