Full-scale post denitrifying biofilters: sinks of dissolved N₂O?

In this study, nitrous oxide (N₂O) emissions from a full-scale denitrifying biofilter plant were continuously monitored over two periods (summer campaign in September 2014 and winter campaign in February 2015). Results of the summer campaign showed that the major part (> 99%) of N₂O flux was found in the liquid phase and was discharged with the effluent. N₂O emissions were highly variable and represented in average 1.28 ± 1.99% and 0.22 ± 0.31% of the nitrate uptake rate during summer and winter campaigns, respectively. Denitrification was able to consume a large amount of dissolved N₂O coming from the upstream nitrification stage. In the absence of methanol injection failure and with an influent BOD/NO₃-N ratio higher than 3, average reduction of N₂O was estimated to be of 93%. The control of exogenous carbon dosage is essential to minimize N₂O production from denitrifying biofilters, in correlation to NO₂-N concentrations in the filter. 

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