Biotrickling Filtration for the Reduction of N 2 O Emitted during Wastewater Treatment: Results from a Long-Term In Situ Pilot-Scale Testing.

Wastewater treatment plants (WWTPs) are a major source of N 2 O, a potent greenhouse gas with 300 times higher global warming potential than CO 2 . Several approaches have been proposed for mitigation of N 2 O emissions from WWTPs and have shown promising yet only site-specific results. Here, self-sustaining biotrickling filtration, an end-of-the-pipe treatment technology, was tested in situ at a full-scale WWTP under realistic operational conditions. Temporally varying untreated wastewater was used as trickling medium, and no temperature control was applied. The off-gas from the covered WWTP aerated section was conveyed through the pilot-scale reactor, and an average removal efficiency of 57.9 ± 29.1% was achieved during 165 days of operation despite the generally low and largely fluctuating influent N 2 O concentrations (ranging between 4.8 and 96.4 ppmv). For the following 60-day period, the continuously operated reactor system removed 43.0 ± 21.2% of the periodically augmented N 2 O, exhibiting elimination capacities as high as 5.25 g N 2 O m -3 ·h -1 . Additionally, the bench-scale experiments performed abreast corroborated the resilience of the system to short-term N 2 O starvations. Our results corroborate the feasibility of biotrickling filtration for mitigating N 2 O emitted from WWTPs and demonstrate its robustness toward suboptimal field operating conditions and N 2 O starvation, as also supported by analyses of the microbial compositions and nosZ gene profiles.