The treatment of wastewater contributes to GHG emissions from the energy consumed to achieve final effluent discharge standards and from diffuse GHG emissions, especially methane during sludge treatment. Wastewater treatment plants are estimated to be responsible for approximately 3% of greenhouse gas (GHG) emissions globally (

Key Benefits

Increase energy self-sufficiency

By treating sludge as a source of renewable energy, plants can save on electricity consumption and improve their carbon footprint. By upgrading its sludge digestion process, the wastewater treatment plant of the city of Lingen in Germany increased its energy production by 31% and, by doing so, reached energy self-sufficiency of 83%. The total carbon footprint of the sludge treatment was reduced by a total of 400 tonnes/year, or by a total of 17%. For more information on how Lingen increased its energy self-sufficiency see the paper ELIQUO recently presented at an IWA conference. In Amersfoort, the wastewater treatment plant with its central sludge treatment facility achieved a 100% energy self-sufficiency:

Prevent diffuse methane emissions

Methane emissions from sludge treatment make up to 75% of the diffuse CO₂-equivalent emissions from wastewater treatment plants (Gärtner 2017). Methane is a strong greenhouse gas with a mass-related greenhouse factor of 28. This means that 1 kg of methane emitted into the atmosphere has the same impact in terms global warming of 28 kg of carbon dioxide. Usually, methane contained in the digested sludge is released to the atmosphere, either during intermediate sludge tank or post thickening storage, dewatering, drying or during land application. Therefore, applying vacuum degassing post digestion, or EloVac®, mitigates the diffuse greenhouse gas (GHG) emissions in the course of the sludge treatment. For more information on how EloVac® helps to mitigate carbon footprint see our paper presented at the Aqua Enviro UK Biosolids conference.

Using sludge as an energy source for the drying

The calorific value of sludge is more than > 10 MJ/kg. Excess heat from the PYREG® unit is reclaimed from exhaust gases. For example, PYREG® 500 module has an electricity demand of 15 kW, but produces usable waste heat of 120-150 kW. This medium grade heat (up to 90°C) helps facilitate the heat balance for the sludge drying process, resulting in a CO₂ equivalent savings of 1,400 tonnes/year or 5,508,757 kilometres driven by an average passenger vehicle.

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