Heat recovery from sewage offers route to low-carbon energy

Heat derived from treated sewage water could be used to heat a housing estate in a first for the UK. Using excess heat recovered from water treatment plant discharge, some 2000 homes will be able to benefit from a low-carbon energy source.

Extracting heat from sewage

Although not finalised, the scheme is under development by a partnership between water utility company Thames Water and the local council for Kingston upon Thames in the south eastern UK.

A first of its kind in England, the so-called “poo power” scheme is part of the planned regeneration of Kingston’s Cambridge Road Estate, including a district heating network.

Under the plans, heat exchangers will recover energy from around a third of the final effluent from the Hogsmill sewage treatment works, which serves some 380,000 Thames Water customers.

“Up to 7 GWh of heat could be recovered every year, saving some 105,000 tonnes of carbon dioxide equivalent emissions over the estimated 30-year lifespan of the project."

Heated from bathing, cooking and other uses, currently the temperature of the final effluent is typically around 10-15°C year-round.

Once the heat recovery scheme is operating the effluent temperature will be chilled to be closer to ambient temperatures while the heat extracted will be circulated in a district network at more than 65°C.

If successful, up to 7 GWh of heat could be recovered every year, saving some 105,000 tonnes of carbon dioxide equivalent emissions over the estimated 30-year lifespan of the project.

Expanding the role of poo power

Once the system is installed it is anticipated that the heating network will expand to include additional public and commercial buildings in Kingston town centre.

These future phases of the district heat network are a key part of Kingston Council’s plans to become carbon neutral by 2038. Kingston Council declared a Climate Emergency in June 2019.

“This is ground-breaking. It’s a first for England and shows we are serious about reducing carbon in the borough. This is a real opportunity,” said councillor Caroline Kerr, leader of Kingston Council.

A final decision on the project is due in the coming months and follows on from extensive feasibility studies over the last two years funded by both the UK central government and the Greater London Authority.

This funding also covered preliminary design work. In the meantime, Thames Water has submitted an application for capital funding from the government. A formal decision on this funding application is due this month.

“This is ground-breaking. It’s a first for England and shows we are serious about reducing carbon.”

“Renewable heat from our sewer network is a fantastic resource,” said Sarah Bentley, Thames Water’s chief executive officer. She added: “We’re confident innovative district heating schemes like this will offer… opportunities to ensure we leave our planet in a better place for future generations.”

Renewable energy sources such as bioenergy, wind and solar, currently generates around a quarter of Thames Water’s electricity needs, saving around £40 million in energy costs each year. The company aims to achieve net zero carbon emissions by 2030.

Support low carbon energy across the EU

If successful, the pioneering Kingston project is expected to be a model for similar schemes elsewhere in the UK. It may also add weight to further developments elsewhere in Europe where district heating schemes are considerably more widespread.

A number of trial projects extracting heat from treated water have already been established in Europe.

For example, in Cologne, a sewage waste heat recovery project was established as part of the European Project CELSIUS. Funded under the 7th Framework Programme, the project assembled a network of 72 cities to help plan, develop and optimise their district heating and cooling networks.

“A number of trial projects extracting heat from treated water have already been established in Europe.”

Cologne’s CO1 demonstrator cost €1,060,000 and was 50 per cent funded by the EU. It consists of three different sites covering 30,000 m² around Cologne – Wahn, Mülheim and Nippes – which use sewage source heat pumps to recover heat. These units were installed from 2012 to 2016.

The Wahn site has a capacity of 200 kW, with a set temperature in the district heating network of 60°C and an annual production of 1,000 MWh, saving about 330 MWh and 20 tonnes of CO2 a year.

Mulheim has a capacity of 158 kW, again with a set temperature into the district heating network of 60°C and a yearly production of 700 kWh. Total primary savings amount to 167 MWh and 22 tonnes of CO2 annually.

Opportunities for waste energy recovery

A similar project was installed in Gothenburg, Sweden at the Rya Värmepumpverk wastewater treatment plant back in 1985. Four heat pumps with a total capacity of 160 MW extract energy from the treated water.

Given the ubiquity of urban wastewater treatment plants and the growing demand for sources of low-carbon space and water heating, there are clear opportunities for waste energy recovery.

Indeed, with more than 350 wastewater treatment works the scope for heat recovery at Thames Water alone is considerable. However, the key to successful development is a suitable source of heat demand such as a district heating network, hospital or others using large volumes of low-grade heat.

In Europe, where district heating is well established in many cities and demonstrator projects are underway, wastewater heat recovery is perhaps more likely to become widespread. Nonetheless, with Kingston leading the way the door is certainly open in the UK too.

Thames Water spokesperson Jamie Presland told Aquatech online: “We believe the scheme can be replicated elsewhere, for example at our other sewage works in partnership with local authorities. At this stage there are no concrete plans to use it on other sites though.”