Abstract
The large global warming potential of nitrous oxide (N2O) is currently of general concern for the water industry, especially in view of a new regulatory framework concerning the carbon footprint of water resource recovery facilities (WRRFs). N2O can be generated through different biological pathways and from different treatment steps of a WRRF. The use of generic emission factors (EF) for quantifying the emissions of WRRFs is discouraged. This is due to the number of different factors that can affect how much, when and where N2O is emitted from WRRFs. The spatial and temporal variability of three WRRFs in Europe using comparable technologies is presented. An economically feasible and user-friendly method for accounting for the contribution of anoxic zones via direct gas emission measurements was proven. The investigation provided new insights into the contribution from the anoxic zones versus the aerobic zones of biological WRRF tanks and proved the unsuitability of the use of a single EF for the three WRRFs. Dedicated campaigns for N2O emissions assessment are to be advised. However, similarities in the EF magnitude can be found considering treatment strategy and influent water composition.
Highlights
Biological processes in wastewater treatment contribute to global warming through direct emission sources over the whole water resource recovery facility (WRRF) area
Biological formation of N2O can mainly result from the activity of heterotrophic bacteria, and of ammonia oxidizing bacteria (AOB) which seem often to be the most effective contributors in N2O production due to their double production pathway (i.e. the nitrite (NO2À) reduction pathway and the incomplete hydroxylamine (NH2OH) oxidation pathway), and their ability to shift depending on the local conditions in the tank
As the Dissolved oxygen (DO) concentrations were generally low, it is unlikely that N2O production was due to incomplete hydroxylamine oxidation based upon the DO concentrations reported by Peng et al
Summary
Biological processes in wastewater treatment contribute to global warming through direct emission sources over the whole water resource recovery facility (WRRF) area. Research efforts have focused on unravelling the specific bio-chemical processes responsible for N2O production (Kampschreur et al ; Schreiber et al ) and the WRRF design and. Biological formation of N2O can mainly result from the activity of heterotrophic bacteria (heterotrophic denitrification), and of ammonia oxidizing bacteria (AOB) which seem often to be the most effective contributors in N2O production due to their double production pathway (i.e. the nitrite (NO2À) reduction pathway (nitrifier denitrification) and the incomplete hydroxylamine (NH2OH) oxidation pathway), and their ability to shift depending on the local conditions in the tank (inter alia: Peng et al ).
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