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Tour(s)plus is reducing its environmental footprint by turning the sludge from its treatment plant into a resource.

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From wastewater to biogas and biogas to methane

The wastewater treatment plant for Tour(s)plus was equipped with digesters in 2006 to reduce the amount of sludge from the water treatment process and produce biogas to heat its installations. However, since the plant was using less biogas than it produced, the surplus was flared. To improve the site’s environmental footprint, Dalkia Biogas upgraded the plant in 2016 by adding a facility able to turn the biogas into biomethane.

A digester and the Dalkia biogas treatment facility

The solution: purify the biogas to produce biomethane

Biogas is created from the breakdown of organic matter by bacteria in an anaerobic environment (i.e. in the absence of oxygen). This reaction is one of the processes used by treatment plants to reduce the amount of organic waste in the sludge resulting from wastewater treatment. This "raw" biogas contains only 50% methane. It must therefore be purified and enriched before it can be used.
Dalkia Biogas installed a biogas treatment and purification unit to boost methane content to more than 95%. This biomethane can be fed into the natural gas network.

How does it work ?

The sludge from the clarification and biological treatment of wastewater is heated to a temperature in which the bacteria can thrive (37°C). It is then broken down in tanks called "digesters" to produce biogas. To turn this biogas into biomethane, CO2 and impurities such as sulphur, ammonia and water must first be removed using processes that include washing and filtering to boost methane content to more than 95%. This methane is then odorised to make it detectable and is either fed into the natural gas network or used as fuel for vehicles.

90 000 €/an

the sale of gas to Dalkia that should be generating

4 KWh

of electricity.


household equivalents.


By turning biogas into biomethane, Tour(s)plus and Dalkia Biogas are actively involved in meeting the targets set by France's energy transition law, which states that 10% of gas consumed should be from a renewable source by 2030. Economic benefits : 8.5 GWh HHV of gas fed into the public network over at least 15 years, with the sale of gas to Dalkia expected to generate annual income of nearly €90,000 for the conurbation community. Impressive energy efficiency: 1 m3 of biomethane = 1.15 litre of petrol = 1.3 kg of coal = 4KWh of electricity. Environmental benefits : 700 household equivalents in the community heated by biomethane, with no CO2 emissions, transport and storage optimised by feeding the gas into the network.



          The biomethane production facility at La Riche treatment plant is the third of its kind in France and demonstrates the determination of the Tours conurbation to turn its infrastructure into shining examples of sustainable development. The facility creates a closed-loop production cycle at the treatment plant by now harnessing all the energy it produces in the process of treating municipal wastewater: people produce waste, the waste produces energy, and the energy is given back to the people. La Riche treatment plant is a shining example of the circular economy.




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