A large sewage treatment plant in Mainz, on the banks of the Rhine River, is to become a lighthouse project for Germany that links the water, green energy and mobility sectors. The fourth stage of water purification – oxidisation – will be transformed by a pilot system that splits water (H2O) into oxygen (O2), to treat the wastewater, and green hydrogen (H2) to feed into the grid.

"The ARRIVED project, i.e. the expansion of the Mainz sewage treatment plant by a fourth purification stage – in combination with an electrolyser – ensures that the Mainz sewage treatment plant will become one of the most modern sewage treatment plants in Germany. This is an environmental milestone," comments Rhineland-Palatinate's Environment Minister Katrin Eder in an article in SolarServer. The state is funding this pilot stage with EUR 170,000.

The planned pilot will include an ozone system, that will eliminate most of the micro-pollutants in the wastewater, and a specialist electrolysis plant. The electrolyser will be powered by various renewable energy sources including solar photovoltaic systems, the sewage gas cogeneration plant and the sludge incineration plant, which is why the hydrogen produced will be classified as “green”.

The next step will be the large-scale implementation of the fourth stage at the Mainz sewage treatment plant, the biggest of its kind in Rhineland-Palatinate. The state has earmarked EUR 6.5 million in subsidies for the project, which is expected to cost a total of EUR 39 million.

There are also plans for an H2 filling station to be built for refuelling vehicles in the municipal fleet, public transport and private vehicles. It is hoped ARRIVED will serve as a model for converting other sewage plants in Germany into clean energy plants, producing H2 for mobility and municipal heating.