Coming soon to your tap -recycled sewage

The Sunday Times
May 10, 2009

Lower rainfall and rising demand could lead to radical measures
By Danny Fortson

Would you like to drink water that has been extracted from the flushings of your toilet? It’s a prospect few would relish. Yet for Londoners it could become reality under a radical scheme being developed to top up the capital’s water supplies.
The idea is one of several being considered by Thames Water in its desperate effort to address the dual threats of a rising population and decreasing rain because of climate change. Today nearly all the 2.8 billion litres of effluent produced each day by the capital’s toilets, dishwashers and showers is treated and then released out to sea. Thames wants to capture some of that and pump it straight back into the system. It has quietly built a pilot plant in north London to test the technology that would make it possible.
Cringe if you like, but experts say drinking processed sewage will be a fact of life as growing populations place more stress on our reservoirs and rivers. Today only 2% of waste water globally is reused.
“Whether you like it or not it’s going to happen,” said David Stuckey, professor of bio-chemical engineering at Imperial College in London. “Even with our climate much of the country’s population is in water-scarce areas, including London. We have 12m to 15m people living in a small area in southeast England but most of our water is in the northwest.”
Thames Water is not alone. Water-starved countries like Namibia and Singapore have been recycling effluent for the past four years. The only such plant in Europe, at Langford in Essex, has been running since 2003. There, Essex & Suffolk Water takes up to 40m litres of waste water a day from a sewage works in Chelmsford, processes it, and releases it into a river before recapturing it downstream and pumping it into the Hanningfield reservoir.
Companies like Suez Environnement and GE have installed systems that recirculate waste water for irrigating crops, but their end product is not suitable for drinking.
A London scheme would be on an entirely different scale and illustrates the extremes that companies, even in moderate climates, expect to have to go to in the coming years. The Environment Agency estimates that nearly half the country, 25m people, live in areas with less water per person than in arid countries such as Spain or Morocco. By 2020 it expects the country’s water needs will have increased 5%.
Thames has begun customer surveys to gauge public opinion. Richard Aylard, head of sustainability at Thames, said: “There isn’t much of a yuck factor. Sewage reuse has been happening naturally for centuries, anywhere there is one city downriver from another.”
The scheme has the blessing of the Environment Agency and it is understoood that several other companies are considering turning sewage into drinking water. At the pilot plant at Deephams in north London, Thames is testing “reverse osmosis” technology. It works by pushing water at very high pressure through a membrane with pores many times smaller than those of human skin. The process strips particulates and toxins to such a degree that the water must be “remineralised” to give it taste. The plant has the potential to purify sewage to a standard that would allow it to be pumped in a direct loop from the sewage works back into reservoirs and aquifers.
Aylard said that if the technology proves successful it could be fitted to several of its big sewage works, including the one at Beckton in east London. The site is Europe’s largest, processing the waste water of 3.5m people each day.
Reverse osmosis has its problems. It is expensive and very energy intensive. Thames said it would be necessary to process the capital’s noxious black water, which is more dangerous than household sewage because it includes sludge from industrial sites such as metal-works and pharmaceutical plants. The Essex scheme, for example, is simpler because the sewage is from a largely residential area.
Part of Thames’s research will test whether reverse osmosis makes sense financially and environmentally. The latter is an important point. According to the Environment Agency, the transport, treatment and heating of water accounts for 6% of Britain’s carbon emissions, about three times that produced by aviation. Water companies will be included in the government’s Carbon Reduction Commitment scheme. From next year they will have to pay for the pollution they produce beyond a certain threshold, so they will be loth to build new plants that will add to their carbon footprint. In addition, the financial crisis has increased borrowing costs for water companies that rely on debt to fund already expensive investment programmes.
Aylard said the idea remains a “contingency option” and would only be resorted to in extreme circumstances, such as a severe drought or a sudden surge in population. He doesn’t expect the company to have to resort to sewage reuse for at least two decades.
Like other water companies, Thames is focusing on more low-hanging fruit first, such as plugging leaks and getting customers to use less water. Londoners are the most profligate users in the country, averaging about 160 litres a day. However, only about three litres of that is drunk. The rest goes down the plughole or the toilet bowl. What’s more, 27% is lost en route because of leaky pipes. Patching up the network will go a long way toward increasing the capital’s supplies.
And there are other membrane technologies, said Stuckey, that are far cheaper but can produce the same standard of cleanliness as reverse osmosis.
What is certain is that our profligacy with water will have to end. But we’ll still have to surmount the “yuck factor”. Stuckey said: “It’s a perception issue. But if marketing companies can convince us to buy things we don’t need, they should be able to convince us to drink water we have drunk already.”