Emission of nitrous oxide (N2O) from sewage sludge incineration plants
The mono-incineration of sewage sludge in a fluidized bed furnace is the technology of choice to implement the phosphorus recycling obligation specified in the Germany’s Sewage Sludge Ordinance 2017. In Germany, about 1.7 million Mg of sewage sludge (dry matter) was generated in 2017 (source: BMU). During combustion, significant amounts of the greenhouse gas nitrous oxide are released due to the low temperatures in the furnace. Nitrous oxide (N2O) is a greenhouse gas (GHG) that is about 300 times more harmful to the climate than carbon dioxide (CO2). In the research report Evaluation and reduction of climate-relevant gases from waste incineration plants (Environment Agency Germany/UBA, UBA Texte 102/2018) emission values between 60 and 290 mg N2O / Nm3 are reported. At the KVA of the ARA in Luzern/Switzerland, 843 mg N2O / Nm3 were measured.
If the entire sewage sludge of Germany would be incinerated in fluidized bed incineration plants, the annual GHG emissions from N2O are calculated in a range from 400,000 to 800,000 Mg CO2-eq (assuming 150 to 300 mg N2O/Nm3). By comparison, in the UBA scenario Greenhouse Gas Neutral Germany, GHG emissions for the year 2050 were calculated to be 60 million Mg CO2-eq. Nitrous oxide from KVA would thus account for 0, 7% to 1.3% of Germany’s GHG emissions in 2050. According to the Environmental Cost Calculation of the Federal Environmental Agency 02/2019 (180 €2016 per Mg of CO2-eq, the annual environmental costs of N2O emissions from the operation of MKVA would be between approx. 70 million € (at 150 mg N2O / Nm3) and 140 million € (at 300 mg N2O / Nm3).
The Regenerative Thermal Oxidation (RTO) process can reduce N2O emissions by 95%. The specific reduction costs for the relatively small plant in Lucerne are around € 92 per Mg CO2-eq. Lower costs are expected for larger systems. The Lucerne-based operators receive a grant from the Swiss Foundation for Climate Protection and CO2 Compensation (KliK) from the Swiss fuel importers. The method used in the plant in Zurich with an increase in the combustion temperature directly after the fluidized bed (combustion chamber or afterburning chamber) is more favorable, but has technical disadvantages.
ifeu scientists currently assess reduction options in the planning for two sewage sludge incineration plants of the Sewage Sludge Cooperation Rhineland (KKR) and the Municipal Sewage Works of the City of Munich (MSE).