N2O generation resulting from piggery air biofiltration

• A biofilter filled with wood chips was tested to treat NH3 emissions of piggery air.
• Biofiltration was suitable for NH3 treatment of piggery air.
• A significant part of the inlet NH3 was converted into N2O.
• Maximal N2O production was around 1 g N2O–N m−3packed-bed h−1.
• No correlation between NH3 removal and N2O generation could be found.

An above ground pilot-scale biofilter filled with wood chips was tested to treat ammonia emissions from a piggery located in Brittany (France). A long-term experiment corresponding to the fattening period was carried out during 124 days (from October 13th 2012 to February 5th 2013) at a constant Empty Bed Residence Time (EBRT = 12 s). NH3 concentrations at the inlet of the biofilter mainly ranged between 8 and 12 mg m−3, which correspond to moderate loading rates (LR from 2.4 to 3.0 g m−3 h−1). After the acclimation period (one month), the biofilter was able to treat the NH3 pollution satisfactorily (removal efficiencies, RE, of around 80%). This study reveals that NH3 biofiltration induced the production of N2O. The N2O concentrations at the outlet of the biofilter were consistently higher than that measured at the inlet, which ranged between 2 and 3 mg/m3 according to the time course of the fattening period. The part of NH3–N converted into N2O–N was estimated as ranging from 10% to 40% while the maximal N2O production was around 1 gN2O–N m−3packed-bed h−1. Although N2O generation seemed to increase with NH3 removal, no correlation between NH3 and N2O could be found.