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When sewage sludge becomes a source of green energy


Today, maximizing the use of by-products from wastewater treatment is a major challenge for the operators and decision-makers responsible for managing wastewater treatment plants. Veolia has developed a sewage sludge recovery solution that makes sludge a resource and establishes local circular economy loops.

The treatment of residual sludge from sewage treatment plants is a challenge that municipalities now have to tackle. They can achieve this by recovering the sludge to produce biogas by a process of thermal hydrolysis and anaerobic digestion.
Transforming sludge into biogas (which is a source of green energy) gives value to materials previously deemed harmful or even dangerous for the environment. It also helps combat the scarcity of raw materials and the use of fossil fuels.

 For sewage treatment plant operators, converting sewage sludge into biogas complies with environmental regulations, drastically reduces residual sludge volumes and creates a new revenue stream, either by using the energy produced on-site, or by selling it to the local grid.

Who are our customers ? 

Local authorities and industry

The Veolia Solution



One of these two global sludge reduction solutions works continuously and the other on demand; both combine thermal hydrolysis and anaerobic digestion.
Thanks to pairing thermal hydrolysis and anaerobic digestion, Exelys™ and Bio Thelys™ offer superior performance in comparison to conventional digestion, and optimize sludge treatment by producing:

→ 25 to 35% less dry matter
→ 30 to 50% more biogas
→ no olfactory nuisance
→ a hygienic, stabilized digestate to control health risks and secure agricultural use.

These two technologies treat all types of organic, industrial, and municipal sludge, as well as fats. They can be added to the other sludge treatment solutions proposed by Veolia, for example for drying these by-products.

Veolia offers a number of technological solutions for the treatment of sewage sludge and energy recovery, including Exelys™ and Bio Thelys™.

Benefits for our customers

Reducing the environmental footprint

Offering an alternative to fossil resources

Providing a source of additional income

Focus Innovation

Exelys™, now available as a package

Following the successful deployment of the Exelys ™ solution, Veolia has innovated with the new Exelys ™ Package. All the benefits of the initial solution are now available in a mobile container facility, suitable for small and medium sized sludge processing plants. 

They chose this solution



Sludge heats the Urumqi plant

The city of Urumqi in China decided to improve its wastewater treatment by modernizing the treatment plant. Under the first PPP signed by the city, Veolia started operating six digesters capable of processing more than 80,000 m3 of sludge and producing 930,000 m3 of biogas per month. This biogas is then used to heat the plant and reinjects 800,000 KWh of green electricity per month into the local electricity network.



Thanks to sewage sludge, the Braunschweig plant is 100% energy-efficient

The wastewater treatment plant in Braunschweig, Germany, is now 100% self-sufficient thanks to the intervention of BSI Energy, a subsidiary of Veolia, which operates the site. It has a population equivalent capacity of 275,000 people. Biological wastewater treatment, thermophilic sludge digestion and co-digestion with organic waste, cogeneration, and recovery of biogas have resulted in the plant being energy self-sufficient.

United States


Thanks to biogas, Gresham saves $50,000 per year

Thanks to Veolia's solutions, the wastewater treatment plant in Gresham, the fourth largest city in the state of Oregon in the United States, has undergone a profound transformation: the most energy-intensive in the city, it has now become 92% self-sufficient thanks to the recovery of biogas from sewage sludge. The plant's electricity costs have dropped by an average of $40 to $50,000 per month.