Greenhouse gases from wastewater treatment plant: towards a new protocol for field measurements

Greenhouse gases (GHGs) emission from wastewater treatment plants (WWTPs) represents an increasing interest in the water industry at the present moment. The biological processes needed for treating wastewater have been found responsible for the unintentional generation of GHGs, such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The quality and quantity of a GHG emitted from a WWTP can significantly vary with the wastewater treated, the process configuration, and the strategies employed in process control. In the recent past, efforts for monitoring and accounting for GHGs emissions from WWTPs have considerably increased, and classifications of emission type were proposed to facilitate reporting. However, knowledge gaps (e.g., N2O production dynamics) and data availability mar the quantification of a WWTP carbon footprint. Moreover, too often the acquired information is insufficient to understand the dynamics responsible for GHG production. Further, it is not even comparable with measurements from different plants due to the heterogeneity of materials, methods, and instrumentation used. For these reasons, in order to produce useful and comparable information for assessing the carbon footprint of WWTPs, there is a crescent need for a generally accepted methodology for GHGs measurement. This paper proposes a comprehensive protocol for monitoring and accounting for direct and internal indirect GHG emissions related to the aerated compartments of biological WWTPs. The proposed protocol also provides important guidelines for quantifying the contribution of anaerobic processes to the carbon footprint of the plant.