How Green Is Your Loo (from The Argus)

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How green is your loo?

The idea of slurping from a toilet bowl is enough to turn anyone's stomach - but we may all have to learn to be less squeamish as water shortages become more common.

Rachel Wareing finds out the true costs of processing our sewage

Toilet-to-tap technology, which turns sewage into drinking water, is starting to look an increasingly attractive proposition in droughtprone areas.

The world's largest water reclamation facility opened last month in Orange County, Southern California.

About 70 million gallons of sewage flows into the plant each day, where it is filtered, screened and subjected to reverse osmosis, hydrogen peroxide and ultra-violet light.

By this stage, the water is pure enough to drink - exceeding all safe water standards - but rather than being delivered straight to residents it is pumped underground and filtered through chalk aquifers. It remains in the ground for six months to a year until it is extracted as drinking water.

At the moment it is a slightly more expensive way of gathering water than the other alternative - importing it from Northern California - though it uses less electricity.

In China, scientist Siqing Xia is working on similar technology. He has constructed a cheap, easily-constructed demonstration-scale treatment plant, which cleanses waste water from one building at his university and turns it into clean water using membrane and bacterial treatment.

Grey water can be reused in the lab or for landscaping - or can be made drinkable through reverse osmosis and ion exchange treatment.

In Sussex, Southern Water also recycles water, but the finished product is not clean enough to drink and so it is pumped out to sea or into rivers.

Toilet-to-tap technology is not considered a viable option.

Southern Water's Jo Osborn said: "It's a technology that's improving all the time but it's not something we are planning to use in the immediate future as we have other methods of supplying water which are less energy intensive - and it's all about reducing carbon right now. It may be that in years to come we will have to look at it."

Water treatment consumes 65,000 gigajoules of electricity a day in the UK - about a quarter of the output of the country's largest coal-fired power station.

One way to make the process less energy-intensive would be to separate out urine.

Urine contains between 50 and 80 per cent of the nutrients which need to be removed from waste water, and these are difficult to extract because they are so massively diluted.

On the Continent, urine separation is catching on. Specially-designed toilets have two waste pipes which divert urine away from mainstream sewage, allowing it to be recycled.

Urine is a great fertiliser, although we produce too much to spray it all directly onto fields. Instead, scientists have been working on ways to extract the useful minerals. In the Netherlands, for example, urine is stored and delivered to special treatment works where the phosphate is removed. This reduces the agricultural need for phosphate rocks, which are mined from the earth at a great energy cost.

If there is less nitrogen and phosphate in the water when it reaches the sewage works, the microbes in the aeration tanks which process the waste water take just one day - compared with about 30 - to do their work, thus saving energy.

The remaining sludge also generates more than three times as much methane which can be converted to energy.

According to civil engineer Jac Wilsenach, who spent six years researching the subject at Delft University of Technology in the Netherlands, separating out half of all urine could turn sewage works into net producers of green energy.

Top 10 water and wee-based facts

URINE separation isn't possible in most homes in the UK just yet, though on a small-scale you could collect your own wee and use it as an organic fertiliser on the garden.

Finnish researchers who used human urine on cabbage crops found growth and biomass were slightly higher than conventional fertiliser. There was no difference in the nutritional value of the cabbage and the practice did not pose any significant hygiene problems or affect flavour.

A LEAKING toilet can use 90,000 gallons of water in a month so keep your kit well-maintained. To check if your cistern is leaking, put a few drops of food colouring in it and don't flush for an hour. If the colouring shows up in the bowl after an hour, you've got a leak.

REDUCE the volume of water used every time you flush by using a toilet brick. Southern Water will send you a free "save-a-flush" bag if you call 0800 0276152.

WHEN you replace your toilet, choose a dual-flush model which enables you to choose between different flush amounts.

THERE are also several devices on the market which adapt cisterns to control the amount of water used, such as the Cistern Dam, Variflush and Mecon. Most cost less than £20 and save up to 50 per cent per flush. Visit www.waterwise.org.uk for a list.

IF YOU live alone or in a laid-back household, you might consider adopting the old Australian maxim: "If it's yellow, let it mellow; if it's brown, flush it down".

PUT tissues, tampons and cotton wool in the bin rather than wasting water by flushing them away.

YOU can re-use water from the bath or shower as soaps are fairly mild and well diluted. A diversion kit will enable you to channel grey water from your downpipe into the garden. Or just use a bucket.

IF YOU want to re-use water from a washing machine in the garden, use a low-sodium detergent. Liquid usually contains less salt than powders. Also avoid phosphorus, which causes algal bloom in ponds and rivers.

CHECK whether urinals in your school, pub or office are working properly. By law urinals should have a device fitted to prevent flushing when the building is not being used but they often go wrong.

Monitoring at Worthing High School found the urinals were responsible for more than 40 per cent of the school's total water use. This rose to 80 per cent as the trial progressed. The problem was traced to faulty urinal controllers.

2:38pm Tuesday 4th March 2008

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