DOGS, unlike people, are capable of pure love—at least according to Freud. As ever more Americans live alone, unconditional affection is in demand. Pet ownership has risen for decades. More than a third of homes have at least one dog, according to the American Veterinary Medical Association. But the popularity of four-legged friends has an icky cost: dogs squeeze out more than twice the waste of the average person, or around 275 pounds a year. With over 83m pooches roaming the country, that is a lot of poop. Around 60% of the stuff gets scooped and trucked to landfills, where it releases methane, a greenhouse gas. The rest delivers surprises to pedestrians and can contaminate waterways, as carnivorous diets create pathogen-rich waste.

The problem is particularly bad in cities, where green spaces are few and lonely souls seeking puppy love plentiful. New York boasts over 600,000 hounds—one for every 14 people—generating over 100,000 tons of turd a year. Some of it smudges unlucky stilettoes, but most is dutifully tossed into rubbish bins and hauled to landfills, at a cost of over $100 per ton. This is a missed opportunity, says Ron Gonen, the city’s former recycling tsar. Now in the private sector, he is trying to launch “Sparky Power”, a programme to transform dog waste into clean energy in the city’s dog parks.

The idea is to fit parks with small anaerobic digesters. Dog owners would place their mongrels’ mounds into the machine, which then converts poo to gas for powering lamps and other park equipment. A year-long pilot would introduce digesters in three parks at a cost of around $100,000. The parks department is pondering the proposal. Similar schemes in other cities have proved short-lived. An underground Energy Transformation Using Reactive Digestion (E-TURD) device created by Arizona State University students for a dog park in Gilbert, Arizona, in 2012 ultimately failed.

“It’s great to turn it into a biofuel, but first you gotta pick it up,” says Tom Boyd, an entrepreneur in Tennessee. His company, Poo Prints, shames the owners of dogs who fail to clean up their messes by testing DNA in uncollected coils. There are enough offenders to secure a new customer every two hours, he says. Most are landlords of smart apartment complexes, but in September the company launches its first district-wide programme—in the London borough of Barking and Dagenham, naturally.