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NXO designs positive energy wastewater treatment plant

Information updated on 20/09/22

NXO, a Montpellier startup, has just developed a wastewater treatment plant that produces the energy it needs to run. A first demonstrator is being installed in September to treat wastewater in the city of Cournonsec.

Photo Cesar Narvaez, Président de NXO ©NXO

Sludge and nutrients from the positive energy wastewater treatment plant (STEP) can be transformed into biomethane, a hydrocarbon that is a source of energy. The process developed by NXO Engineering, a startup based at the Cap Omega incubator facility, leverages the fact that “wastewater carries calories, carbon, nitrogen, and phosphorous,” as explained by César Narváez, the company’s president. “

Our approach uses those aspects to produce more energy than it takes to treat wastewater.”


Their model is based on bioreactors and bacteria symbiosis with micro-algae. The gas they produce is transformed into an energy resource that is enough to cover the energy used for treatment. “To treat wastewater in activated sludge pools, it is necessary to oxygenate the environment. That operation by itself accounts for nearly 62% of the cost of treating wastewater,” adds César Narváez.

Partnership with research centers
The cost savings of having bacteria work with micro algae is also intended to bring down the cost of drinking water, of which about 40% is related to treatment. A 100-population equivalent plant installed in Cournonsec in mid-September will serve as the first live demonstrator. “We are targeting communities that would need a STEP solution for a population equivalent of 1,000 to 10,000,” says César Narváez. The company is also looking at the hospitality sector, as well as industry and military applications.
Founded in 2016, and incubated by Montpellier BIC, the startup is working in partnership with University of Montpellier and research centers such as CNRS, the Narbonne Laboratory of Environmental Biotechnology, and Ifremer in Sète. This eco-solution has received support from Montpellier Métropole, the Hérault Department, the Water Agency, and the Occitanie Region.

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