Dog poo biogas digester
in Greener Homes on 5 August 2012
A Melbourne man is harnessing another kind of Diesel power.
DUNCAN Chew had an epiphany, at his local park in Hawthorn East, at the most unexpected moment: while watching people try to jam dog poo into two overflowing bins.
“People were putting the bags next to the bins or on top of them. It was ridiculous – we have all this biodegradable waste that ends up in landfill. I thought, ‘There has to be a different way’.”
Mr Chew owns two boxers, Sally and Diesel. He could relate to his fellow dog owners’ predicament. “They’re quite large dogs and, to put it bluntly, they poo a lot,” he says.
He recalled a presentation he’d seen about composting toilets, and figured it must be possible to do something similar with dog poo.
With further research, he found that Australians have a high rate of dog ownership and that everyday, we have to dispose of about 1350 tonnes of dog shit.
Now, courtesy of a federal government grant, he’s knee-deep in planning to build a methane digester in Edinburgh Gardens, in Fitzroy, together with the Yarra Energy Foundation.
The technology isn’t new – it’s been in use for thousands of years. Designs vary, but in general terms, a biogas digester is a system where biodegradable material, such as manure or food waste, breaks down without oxygen, and in doing so, produces methane.
In Mr Chew’s scheme, called Poo Power, the methane will provide the energy for a light in the park, or possibly for heat or a small amount of electricity. He hopes to have it running by summer, together with an education program.
“It’s a conversation starter,” he explains. “It will get people talking about science and renewable energy, and about waste and waste sanitation. I think it will bring some much needed fun and levity to the public debate about sustainability.”
It’s true: the topic doesn’t seem substantial (its pun-to-weight ratio is off the chart). But the matter of manure is actually a heavy one. The American farmer and writer Gene Logdson argues that we’ve “lost touch with the animal digestive system, including our own”.
In his book Holy Shit: Managing manure to save mankind, he writes about using manure to boost soil fertility, in the manner of many previous agricultural traditions. He says the practice will become increasingly important as the price of chemical fertilisers and mined phosphorous (supplies of which are dwindling) rise.
In a similar way, Mr Chew’s project is motivated by his belief that for many city-dwellers, dogs are our closest link with the rhythms and cycles of the natural world.
Mr Logsdon says pet scat is not without its virtues. “Dogs like to gnaw on bones and bones are rich in phosphorus, so dog dung is actually one of the more valuable manures as fertiliser,” he writes. “And since cats like to eat meat and fish, this manure would have a full complement of nitrogen in addition to its above-average phosphorous content.”
He advocates for composting our pet poo, rather than putting it in rubbish bins and into landfill. To do it well, add a mix of materials, both brown (dried leaves, straw, cardboard) and green (grass cuttings, manure). It’s probably most convenient to slowly add to a pile and make sure you “let the compost age for a year or two without heat to get rid of pathogens and worm eggs”.