Ammonia biofiltration and nitrous oxide generation during the start-up of gas-phase compost biofilters

Gas-Phase Biofiltration technology is widely utilized for treating ammonia gas (NH3) with one of its potential detrimental by-products being nitrous oxide (N2O), a potent greenhouse gas (100-y radiative forcing 298 times greater than carbon dioxide). The present work was conducted to investigate the relation between NH3 removal during biofiltration and N2O generation as a product of incomplete denitrification during the start-up of gas-phase compost biofilters. Four laboratory scale tubular biofilters in up flow mode (20 s residence-time) were studied for 21 days: 3 replicates were subjected to 16 ppmv (0.78 g m−2 h−1) of NH3 and a statistical control not subjected to NH3. Ammonia concentration differences between biofilter inlet (Bottom = 16 ppmv) and outlet (Top) and N2O concentration differences between biofilter outlet (Top) and biofilter inlet (background concentrations at the bottom) were used to determine the extent of the correlation between NH3 removal and N2O generation. Correlations with CH4 and CO2 were also reported. The high Spearman correlation coefficients for the three replicates (ρ = −0.845, −0.820, and −0.841, with P ≤ 0.0001 for replications A, B and C, respectively) suggested that availability of nitrate/nitrite owing to NH3 nitrification favored conditions for N2O generation as a sub-product of denitrification. The statistical control received no NH3 inputs and did not generate N2O. Therefore, the results indicated that the process of NH3 removal was a trigger for N2O production. Carbon dioxide and N2O were moderately correlated. Methane and N2O were weakly correlated and only for replicate C. No significant correlation was found for the Statistical Control between N2O and CH4.