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An innovative solution converts sewage sludge into gas

Posted on 13 November 2018.

In Avignon, Veolia has experimented with a new tiered gasification technology to transform sewage sludge into gas. After three years of research, the "AdWastetoGas" results look promising.

Every year, around 15 megatons of liquid sludge are produced by French wastewater treatment plants. Waste that Veolia helps reduce by recycling it as heat or electricity.

Although anaerobic digestion is an already tried and tested process, since 2015 the Group's Research & Innovation teams have been experimenting with a new solution for recycling sewage sludge. A pilot project named "AdWastetoGas" was set up in the Courtine wastewater treatment plant in Avignon to test the potential of staged gasification. The goal was to evaluate the potential of converting sewage sludge into high quality energy-efficient synthesis gas.

How does this innovative process work? Gasification consists of transforming a solid material into gas by subjecting it to a very high temperature. First step: mix the sewage sludge with dry matter – for example wood waste from farms.

The mixture is then fluidized using a mixture of steam and oxygen and heated to 700-1000°C. The effect of the heat is to considerably reduce the mass of the sludge and naturally generate energy rich "syngas" - synthesis gas.

The important thing to remember about the process is that the mixture is not burned but oxidized – it simply degrades in the presence of oxygen. This helps to avoid the release of CO2 and ensures low environmental impact.

A gasification reactor was installed in Courtine's sewage treatment plant in Avignon, where a team of researchers were specially assigned to conduct the project.

For a little over a year the experts evaluated the quality of the gas produced based on the nature of the waste and the process conditions. Completed at the end of 2016, the tests demonstrated the technical feasibility of the process in terms of producing a high energy potential gas, rich in fuel (hydrogen, methane).

By using the energy generated from their own waste, wastewater treatment plants could in the future reduce their environmental impact along with their energy bills. Ultimately, experts even believe that by recovering their sewage sludge some plants could become energy self-sufficient.

This research and innovation process responds to Veolia's desire to gradually make its various wastewater treatment sites energy independent.