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Poo potential ‘untapped’ says Thames Water boss

Water firm chief exec tells London Assembly sewage could become a new source of renewable energy, reports Noah Vickers, Local Democracy Reporter

Cathryn Ross (credit Thames Water)
Cathryn Ross (credit Thames Water)

Warm sewage presents a “tremendous, untapped” opportunity to generate green energy, the boss of Thames Water has said.

Cathryn Ross, the company’s interim joint chief executive, told City Hall politicians on Wednesday (13th) that liquid waste – or effluent – had huge potential to help cut carbon emissions.

Ross told the London Assembly’s environment committee: “We think that the effluent that we have within London alone could generate ten terawatt hours of wastewater heat.

“To give you a feel for that, that’s the equivalent of 40% of Hinkley [Point] C [nuclear power station]. That’s a tremendous, untapped resource.”

She added: “The technology’s actually quite simple, because basically all you’re doing is using the fact that effluent is relatively warm – because of where it comes from – and you put a heat inverter around the sewer pipe, and you can extract the heat from that.”

Although putting the technology into practice is still at a “fairly early stage”, Ross said it has a “tremendous potential to contribute to the decarbonisation of heat, which of course is one of the biggest challenges we face”.


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Asked by Liberal Democrat member Hina Bokhari whether the cost savings created by such a project would benefit Thames Water’s customers when they receive their bills, the CEO confirmed that it would, saying that it was a regulatory requirement for schemes of that kind.

The company’s handling of sewage came under fresh scrutiny earlier this month, after a BBC investigation found that it and two other English water companies discharged wastewater hundreds of times in 2022, including for a total of 3,500 hours when the weather was dry.

The Environment Agency is carrying out its own criminal investigation into potentially illegal discharges by all water companies.

The aim of the City Hall committee’s meeting however was to discuss ways in which the Thames and other London rivers could be better utilised to cut carbon emissions. London mayor Sadiq Khan has said he wants London to achieve net zero carbon by 2030.

Ross told the committee about two other opportunities for the firm to generate green power, including a “gas-to-grid” system potentially capable of heating up to 21,000 homes, and placing floating solar panels in reservoirs within the M25.

The latter measure, which could be deployed across 19 square kilometres of reservoir surface, has the potential to generate up to one gigawatt of power, she said.

At an earlier point in the meeting, the CEO apologised for the same day’s water outage in west and south-west London, pledging that the company would conduct a review both into the cause and their attempts to respond to it.


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