Energy balance and greenhouse gas emissions of municipal wastewater treatment systems

An increased concentration of greenhouse gases (GHG) in the atmosphere leads to global warming and thus to a change of the earth’s climate. A global and common approach in an interdisciplinary manner is necessary to decrease its impact to an acceptable level.

Municipal wastewater treatment plants are emission sources of anthropogenic greenhouse gases such as carbon dioxide, dinitrogen monoxide and methane. Carbon dioxide can either be formed directly during the oxidation of organic matter and endogenous respiration, or indirectly by the energy consumption of the wastewater treatment plant. Dinitrogen monoxide is usually released as a natural intermediate during biological wastewater treatment and released to the atmosphere in turbulent areas of the treatment plant. Methane can already be produced in significant amounts in the sewer system reaching the wastewater treatment plant in dissolved form. As well as dinitrogen monoxide, methane can be emitted through turbulent areas of the wastewater treatment plant.

So far there is little data available on greenhouse gas emissions from wastewater treatment plants. This is due to the fact that measuring techniques, such as the Fourier transform infrared spectroscopy (FTIR), are very complex and cost intensive. In this context, there is a need to develop methods for the quantification of greenhouse gas emissions to find emission sources and ways of mitigation, in order to bring the energy optimization of wastewater treatment systems forward.

In the first part of the research project a new method will be developed, in which the dissolved greenhouse gases can be quantified in a wastewater sample by salting-out. By means of mass balances it will be then possible to determine the potential of wastewater treatment plants to emit greenhouse gases.

In the second part a dynamic model will be developed for predicting greenhouse gas emissions for an overall wastewater treatment plant. The simulation will be conducted using the simulation software SIMBA#water (ifak). The basis for the modeling in this case forms the ASM3 ("Activated Sludge Model No. 3").