Thames Water

Jane Bordenave discovers how Thames Water, the UK’s biggest water company, is turning its customers’ flushes into energy and cost savings via its Poo Power initiative.

It’s not your standard topic of conversation, and almost certainly the sort of subject your mother told you to steer clear of in polite company, but Thames Water’s Poo Power initiative is big news. As the UK’s largest water utility, the company has 13.6 million customers and treats 2.8 billion litres of sewage every day. Through Poo Power and related projects, the company is putting this waste to work.

“Poo Power is thought to have been going in some form or another for millennia,” explains Simon Evans, Thames Water’s press office manager. “We believe biogas derived from poo was used to heat bath water in Assyria as far back as the tenth century BC.” The more technologically advanced use of treated human waste and biogas products as a source of power began around the end of the Second World War and extended to a biomethane car. While it hasn’t moved into transportation just yet, Thames Water is however investing millions in the development of this resource.

There are two ways of capturing energy from treated sewage. The most common is anaerobic digestion, also known as CHP (combined heat and power). This process involves separating the sludge from the waste water at the treatment plant and putting it into an anaerobic digester. Once inside, it is heated to produce an accelerated composting effect, releasing the methane which is then burned to produce energy. Twenty-one of the company’s 349 sewage works run on this system.

The second, less common, process is thermal destruction with energy recovery—where sewage sludge is dried into blocks of ‘cake’ that are also burned to generate power. Currently, the only plants using this system are Crossness and Beckton in East London; however, as Evans explains, this is no mean feat. “These are not only our two biggest sewage works, serving two million and 3.5 million customers respectively, but Beckton is in fact the largest in Europe.”

Prior to the installation of these Poo Power plants in 1998, treated sewage was dumped at sea; however, this had the effect of over-nourishing the Thames Estuary and risked upsetting the ecological balance of the water. “Given this situation, we had to find a solution that would allow us to use the sludge in a beneficial way, but also to get rid of it. Having lorries transporting the waste outside of London would have been impractical, so we decided to construct the incinerators and use it ourselves.”

The Poo Power project has saved Thames Water £15 million in energy bills—15 per cent of its total 13,000 gigawatt hour per annum energy needs. “Clearly, this has a downward, trickle-through benefit for our customers,” says Evans, “as by saving money on running costs, we are able to pass on those savings.” As part of its ongoing commitment to reducing its carbon footprint, Thames Water is planning to make additional investments to bring this total up to 20 per cent, further reducing its consumption of fossil fuel generated energy supplied through the National Grid.

Energy generation and subsequent cost savings are not the only benefits brought about by finding a use for the end product of sewage treatment. Farmers around the Thames Water region benefit by purchasing the baked poo from the CHP process to use as fertiliser.

“Clearly, we’re not talking about raw sewage here,” says Evans. “In fact, to see it or even handle it, you wouldn’t recognise it as a by-product of waste water treatment. And it has all-round benefits: we are able to dispose of the sludge from the treatment works that don’t use thermal destruction; the farmer has access to large amounts of natural fertiliser; and the consumer is safe in the knowledge that their waste is being used in a way that is beneficial to the environment and, in the end, beneficial to them. Albeit not without a certain ‘yuck factor’ to overcome.”

While the fertiliser side of this equation has been established for a number of years, the company has also recently established a relationship with two energy companies—British Gas and Scotia Gas Networks. The three utilities will work together to create five biomethane demonstration projects, which will be the first in the UK to inject green gas into the grid. The announcement follows government backing for this emerging technology, confirming support for biomethane to grid from 2011.

The first of these plants will be constructed at Didcot Sewage Works and, once completed, what the citizens of Didcot flushed away 23 days ago will be helping to heat their homes. If the experiment works well, a rollout across the country could result in biogas forming 15 per cent of the country’s gas supplies by 2020.

There’s no doubt that human excrement is a delicate subject, but when it comes to finding a use for what is considered by most to be 100 per cent a waste product, there’s nothing to be shy about. What the Thames Water Poo Power initiative shows us is that every day we are effectively producing a source of clean energy—even if we might not think of it that way! Injecting the gas released through CHP back into the National Grid while using the solid remains as fertiliser closes the carbon cycle, which is essential if something is to be described as ‘green’, ‘sustainable’ or ‘renewable’.

Environmental awareness and responsibility require us to be ingenious and also to examine methods of using what we consider to be waste. Poo Power fulfils both of these obligations and, while we may be squeamish about it at first, it is a source of energy and plant nutrients that we can all benefit from, directly or indirectly. Who knows—perhaps one day we will see the return of the biomethane car. www.thameswater.co.uk