Reducing carbon paw prints

2010-12-29 00:00

OVER the past few years we have become more aware of the environment and our impact on it. Many people have been moved to change aspects of their daily lives in a bid to reduce their carbon footprint on the planet.

But what about the “paw print” of our pets? The environmental impact of dog waste has only recently been recognised. “If you have a German shepherd or similar-sized dog, for example, its impact every year is exactly the same as driving a large car around,” says Professor Brenda Vale, an architect from New Zealand’s Victoria University who, together with her husband Robert, specialises in sustainable living.

In a study the Vales published in New Scientist, it was calculated that a medium dog eats 164 kilograms of meat and 95 kgs of cereals every year. It takes 43,3 square metres of land to produce one kilogram of chicken a year. This means it takes 0,84 hectares to feed Fido. This was compared with the footprint of a Toyota Land Cruiser, driven 10 000 km a year, which uses 55,1 gigajoules (the energy used to build and fuel it). One hectare of land can produce 135 gigajoules a year, which means the vehicle’s eco-footprint is 0,41 ha — less than half of the dog’s.

We all love our dogs. They give us their unconditional love, they protect us and they can even reduce our high blood pressure. But we also hate the smelly, unpleasant and difficult-to-eliminate piles of faeces that our furry friends leave behind.

Unfortunately dog waste is not only an inconvenience but an environmental and health problem too. Take the environmental impact of dog waste on landfills.

Consider the actions of the good citizen walking his or her dog in a residential area or in a park. Sooner or later the dog will stop for a couple of minutes and when it walks away, there will be between 100 grams and 500 grams of poop left behind. We expect this to happen outside our homes and we train our dogs to defecate accordingly, often taking them for a walk especially to do it.

Post poop the good citizen likely uses a plastic bag to pick up the dog deposit, ties it off as tight as possible to avoid the offensive odour and throws it in the nearest waste bin. From there it gets transported to a landfill, where the poop remains in the plastic bag, never to biodegrade. When you consider that in residential areas almost all households have dogs, you’ll realise that there’s a lot of dog poop going to the landfill. Once the waste is in the landfill it is not eliminated but rather shifted from being our personal problem to a problem for the whole community endangering underground water, wildlife and humans.

Dog droppings left unattended present even greater danger. This can spread disease to local wildlife and the risk of contamination of local water supplies. The greatest health concern associated with animal wastes is pathogens. Many pathogens found in animal waste can infect humans if ingested.

Some of the parasites your lawn could harbour originate from dog poop. Infections from Cryptosporidium, Giardia, salmonella, as well as hookworms, ringworms and tapeworms often cause fever, muscle aches, headaches, vomiting, and diarrhoea in humans. Children are most susceptible, since they often play in the dirt and put things in their mouths or eyes.

The collection, bagging and disposal of doggy poop is unpleasant enough, but what then? Placing any plastic bag full of waste in landfills is far from ideal. According to the Australian Department of Environment, the benefit in using degradable plastic bags is questionable as they may not break down in the dry, oxygen-starved conditions found in most landfills, and if they do, may produce methane, a potent greenhouse gas.

Most people are unhappy throwing poop into the waste bin but are often unaware of the alternatives.

One environmentally friendly and cheap solution to the poop problem appears to be the worm farm. Composting worms are housed in a simple box and are fed dog poop, lawn clippings and kitchen scraps. The worms remove any odour and convert this organic waste into worm castings: a nutrient-rich organic fertiliser. However, this is not without problems — the worm farm requires maintenance and if there is an excessive amount of dog poop — from more than one or two medium-size dogs — the worm-farm route is not recommended.

If you do go the worm-farm route, one important note: do not place dog poop in the worm farm straight after deworming your dog as the medication will kill your worms.

A common approach to dog waste “treatment” is to add it to the garden compost pile. Definitely not a good idea, as parasites are frequently present in the faeces of flesh-eating animals.

So what’s the ideal solution? Local bioagronomist Nick Snaith, who runs East Coast Organics, has designed what he calls a “decompoohzer” which works like a miniature septic tank, digesting dog waste to a liquid that can be absorbed into the surrounding soil.

The decompoohzer is a double-chamber vessel, rather like a medium-size plastic bin, that is installed in the ground. Inside the inner chamber, dog poop is soaked in water containing what’s called a “natural digestion microbial culture” designed especially for dog waste. The decomposition takes place in the absence of oxygen which leads to odour elimination and deactivates the pathogens. The liquid overflows into the secondary chamber free of solids and odours, and then flows out of holes at the bottom of this chamber into the soil.

“Dog poo is no good for compost,” says Snaith. “Nutritionally it is hopeless. Dogs are scavengers, like hyenas, and they don’t release any nutrients in their faeces, they absorb it all. Secondly, dog poo is a prime source of pathogens.”

The solution is to add bacterial microbes that provides the right balance for breaking down dog waste.

The decompoohzer provides the meeting place for the bacteria and the dog waste. “You just fill it with water, add the dog poo and pour in the microbes,” says Snaith. “This is a dry powder that comes in a sachet. Thereafter you simply put in the dog poo on a daily basis. The microbes eat it up and break the solids down, eventually liquid overflows from the inner into the outer chamber and from there seeps down into the ground.”

The decompoohzer, which has a volume of 55 litres and costs R400, comes with instructions on installation. It is placed into a hole dug into the ground and rests on a bed of gravel which extends upwards just past the irrigation holes. Then the rest of the hole is filled with soil. The decompoohzer is designed so that you can lock the opening at the top to prevent children putting their hands inside and if you want to disguise its presence a slab of synthetic grass should do the trick.

“We have the one size at the moment capable of servicing four big dogs in the garden,” says Snaith. “If you put one of these at the bottom of a tree it will use whatever comes out for it’s benefit.”

• Additional reporting by Stephen Coan. To know more about the decompoohzer contact Nick Snaith at

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