©Phototheque VEOLIA : Stéphanie Lavoué

Biogas turns into electricity in Montpellier

Posted on 14 October 2016.

In Maera, near Montpellier, Veolia converts sewage sludge into electricity and heat to run the circular economy.

In 2009, as part of its sustainable development and renewable energy policy, Montpellier Agglomération (now Montpellier Méditerranée Métropole) decided to initiate "a comprehensive approach to saving energy and reducing greenhouse gas emissions" for the Maera wastewater treatment plant.

So the city asked Veolia to recover the biogas produced by sewage waste - installing a cogeneration plant to produce energy in the form of electricity and heat.

Using excess biogas

Commissioned in 2005, the Maera plant now receives wastewater from 18 communities in the Montpellier urban area, equivalent to a population of about 470,000 people.

Operated by Veolia, it is the largest wastewater treatment plant in the area, and like any such facility, it produces significant quantities of sewage waste. Sludge mainly, which is collected during the water depollution process. Treated through a special pathway, the sludge generates biogas via the digesters.

Before installing the cogeneration unit in 2011, some of this biogas was used to fuel the boilers that heated the sludge for digestion. The surplus - up to 70% - was flared. An energy source begging to be exploited, given that biogas contains mostly methane, a gas with a high calorific value. It was therefore important to recover it and so further optimize the management of the treatment plant’s resources.

Maera: a circular economy success

Recovering biogas by means of the cogeneration unit not only supplies heat for the digesters but also produces electricity which is then sold to EDF as green energy. In 2015, Maera generated 3 million m3 of biogas and 6.7 million kWh of energy, covering over 50% of the electricity consumption of its facilities. Since it was commissioned, the cogeneration unit has produced over 21,500 MWh of energy.

Finally, Veolia also installed a unit to take and pre-process fatty waste - such as that from restaurant grease traps – which is treated in the digesters along with the sewage sludge. This increases the production of biogas while ridding restaurateurs and manufacturers of effluents that are particularly problematic.