Methane and nitrous oxide emission from different treatment units of municipal wastewater treatment plants in Southwest Germany.

Azzaya Tumendelger,Andreas Lorke,Zeyad Alshboul,Eiko Eurya Kuramae

doi:10.1371/journal.pone.0209763

Abstract

We measured the atmospheric emission rates of methane (CH4) and nitrous oxide (N2O) in two wastewater treatment plants in Southwest Germany, which apply different treatment technologies. Dissolved gas concentrations and fluxes were measured during all processing steps as well as in the discharge receiving streams. N2O isotopocule analysis revealed that NH2OH oxidation during nitrification contributed 86–96% of the N2O production in the nitrification tank, whereas microbial denitrification was the main production pathway in the denitrification tank in a conventional activated sludge (CAS) system. During wastewater treatment using a modified Ludzack-Ettinger system (MLE) with energy recovery, N2O was predominantly produced by the NO2- reduction by nitrifier-denitrification process. For both systems, N2O emissions were low, with emission factors of 0.008% and 0.001% for the MLE and the CAS system, respectively. In the effluent-receiving streams, bacterial denitrification and nitrification contributed nearly equally to N2O production. The CH4 emission from the MLE system was estimated as 118.1 g-C d-1, which corresponds to an emission factor of 0.004%, and was three times lower than the emission from the CAS system with 0.01%.

Highlights

Sewage treatment is an important source of anthropogenic greenhouse gases with significant amounts of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) being released during wastewater treatment [1]
While the latter emissions are considered as short-cycle CO2 that does not contribute to increasing atmospheric CO2 concentrations [1], the emissions of CH4 and N2O from waste water treatment plants (WWTPs) contribute to the anthropogenic increase of atmospheric greenhouse gas concentration
The distribution of dissolved inorganic nitrogen (DIN) species (NH4+, NO2- and NO3-), DN2O and dissolved oxygen (DO) in the water from different sampling points at both WWTPs are presented in Figs 2A, 2B, 3A and 3B, respectively

Summary

Introduction

Sewage treatment is an important source of anthropogenic greenhouse gases with significant amounts of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) being released during wastewater treatment [1]. CO2 is produced both indirectly as a result of fossil fuel combustion for energy generation that is required for the operation of waste water treatment plants (WWTPs), and it is produced during the degradation of organic matter during the treatment process. While the latter emissions are considered as short-cycle CO2 that does not contribute to increasing atmospheric CO2 concentrations [1], the emissions of CH4 and N2O from WWTPs contribute to the anthropogenic increase of atmospheric greenhouse gas concentration.

Methods

Results

Conclusion