Sideways News

Could the outhouse really come back into fashion?

Should we be turning human waste into precious fertiliser, instead of flushing it all away?

How does it work?
A compost toilet is a dry or waterless toilet, which means water is not used to take the waste elsewhere.

A typical compost toilet has two chambers; owners use one chamber for a year then switch to the second chamber to allow the contents of the first to decompose (bacteria breaks down the contents). The valuable end product - sometimes known as humanure - can be used instead of fertiliser for your plants and trees. It’s also free.

Saving on waste
Compost toilets save resources - water, electricity and fuel - as the solid waste is dealt with onsite. It is not piped out to a sewage farm to be treated or pumped out of a septic tank by a fuel-operated truck.

"Composting toilets create no waste but instead a fabulous resource in nutrient-rich compost," says Marcus Zipperlen, Head of the Biology Department at the Centre for Alternative Technology in Wales, where he regularly hosts public courses on water and sewage treatment.

In an average household, toilet-flushing accounts for one-third of domestic water use - which stands at 150 litres per person, per day in the UK. What’s more, the UK uses about 3% of its electricity processing water - the output of a large power station.

Do you dare?
Commercial compost toilets include high-tech features such as electric fan ventilation, heaters to speed up the composting process, or mechanical mixing. However, more low-tech models are just as effective.

John Cossham has been using a self-constructed, low-tech compost toilet in his back garden in York since 2002. "The Humanure Handbook showed me I didn't need to build anything, all I needed really was a bucket, a compost bin and some cover material." His system is made up of a second-hand commode, a brewing bucket and four large compost bins.

A lot of hard work?
Becoming responsible for your body's waste from start to finish can be a tricky business. It can seem like hard and messy work: after each "deposit", you need to spread sawdust or straw into the toilet as bacteria like to eat a balanced diet of carbon and nitrogen.

The science behind the smell
Since human waste contains a lot of nitrogen, if it doesn’t get enough carboniferous material (like sawdust, straw, hay, shredded paper) it will give off excess nitrogen in the form of ammonia, which makes the loo smelly.

Keeping urine separate is also key to a successful composting system. If the urine is not separated from the faeces there is too much nitrogen to allow for effective composting and the collected material can get too wet and odorous.

Zipperlen confirms that when "poorly designed", composting loos "can smell terrible, breed flies, and be thoroughly unpleasant". They take up a lot of space too, he adds. And though composting toilets solve the problem of blackwater, there is still the issue of greywater (which will need to be treated).

Making proper use of your toilet
The Environmental Protection Agency in the US has published a composting toilet factsheet. Among rather insignificant shortcomings of composting toilets, such as the possibility of seeing excrement, it also warns that "using an inadequately treated end-product as a soil amendment may have possible health consequences". Experts counter this by saying that as long as the toilets are used properly, they can kill any waste-borne pathogens.

Lastly, if your compost toilet is outside (they're very difficult to retrofit into an existing house), having to go outside in all weathers can be a strain.

"The commitment comes when it is cold, wet or dark outside and it feels easier to be lazy and go to the flush toilet inside," says Cossham.

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