Gas engines at wastewater treatment plants

Changing the biogas engines

Two CHP units are in operation at the Mühlbach wastewater treatment plant. These machines produce heat and electricity from the methane gas produced during wastewater treatment.
The gas engines in Mühlbach deliver a total output of 190kW, of which 60kW is electrical and 99kW is thermal.

At best, these engines run around the clock to ensure the plant's own supply of heat and electricity.
To ensure that they remain operational around the clock, they must of course be maintained. Just like a car, oil and filters have to be changed and valve clearances adjusted, for example. This work is carried out by the plant personnel themselves.

Changing the biogas engines — combined heat and power unit

End of service life reached

At some point, however, these engines reach the end of their service life and have to be replaced. In Mühlbach, both gas engines were replaced with new ones in February 2025.

To do this, the CHP plant is completely dismantled, the old gas engines are removed and the new engines are reinstalled.

End of service life reached — New gas engine and old engine

Limits must be adhered to

After commissioning the CHP units with the new gas engines, it is not enough for the machine to produce heat and electricity again; the exhaust gas limits must also be complied with. The Office for Air and Noise has specified these limit values in the emission permit.

An external specialist company carries out an annual analysis of the exhaust gases at the ARA Pustertal AG plants. These measured values must also be reported to the office.

Limits must be adhered to — Exhaust gas measurement

Sustainable energy production

The biogas engines fulfill an important purpose at sewage treatment plants: the biomethane gas (CH4) produced in the purification process would be too good not to use. What's more, methane is around 28 times more harmful to the climate than CO2!
This is why methane is converted to CO² in these units, and the resulting thermal energy enabled the ARA Pustertal AG wastewater treatment plants to cover 100% of their heat requirements and 81.7% of their electrical energy requirements in 2024.

In 2024, all ARA Pustertal AG CHP plants produced 7.763 GWh, which is roughly equivalent to the annual requirements of 2,200 households.
This energy is produced in a climate-neutral way, as the organic components in the wastewater mainly come from biological sources.

In this way, ARA Pustertal AG not only purifies the wastewater, but also keeps the air clean.