Sludge treatment and recovery

Wastewater: reducing sludge volume and reusing it

As the end-product of wastewater treatment, sludge is a major economic and environmental concern. SUEZ ENVIRONNEMENT provides its customers with a wide range of processes from digestion to incineration, thickening, dewatering, composting or drying. The aim is to reduce the volume of sludge produced, but also to:

• reuse it for agricultural purposes, enriching the soil without fossil fertilizers and reducing the carbon footprint from fertilization;
• recover its energy potential in the form of biogas.

Terralys is helping to implement the FERTI 16 composting unit for the urban community of greater Angoulême (France). This plant is capable of processing 11,000 metric tonnes of sludge per year, using the windrow method (in which material is turned for ventilation) to reduce energy needs.

In 2010, Ondeo IS also launched Biocontrol+, the new version of its method of reducing industrial sludge. With BioControl+, Ondeo Industrial Solutions offers manufacturers a solution that reduces sludge production by up to 90%.

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Turning dried sludge into energy

Once dried, sewage sludge can also be recovered for energy. Since the sludge produces biogas, it is an alternative to fossil fuels (oil, gas, coal) and its calorific value is comparable to wood.

Degrémont offers a pyrolysis gasification process, in which gas and fumes from sludge provide heat. The SIAAP Seine upstream plant in Valenton (France), which has a processing capacity of 4.6 metric tonnes of dried sludge per hour, uses this innovative process to recover 60 GWh/year of thermal energy. Lyonnaise des Eaux also offers comprehensive renewable energy production with sludge methanization at the Grande Synthe sewage treatment plant in Dunkirk and the construction of wind turbines in Calais.

Safely disposing of sewage sludge

SUEZ ENVIRONNEMENT provides innovative and economical solutions for eliminating the sludge produced by wastewater treatment, with the help of thermal treatments.

In 2008, for example, Degrémont installed Themylis™ 2S on the site of the wastewater treatment plant in Gdansk (Poland). This innovation combines incineration furnaces and pre-drying to reduce fuel consumption efficiently. The energy recovered from the fumes in a heat exchanger is used to preheat the sludge. This coupling of pre-drying and heat recovery from fumes significantly reduces CO₂ emissions.

Since its installation, the process has resulted in savings of €1 million per year and helped eliminate 6,800 metric tonnes of greenhouse gas emissions (CO₂ equivalent).