Mitigation of N 2 O emissions via enhanced denitrification in a biological landfill leachate treatment using external carbon from fermented sludge

The effects of an external carbon source (C-source) on the mitigation of N O gas (N O ) emissions from landfill leachate were investigated via enhanced denitrification using anaerobically fermented sewage sludge. Anaerobic fermentation of sewage sludge was conducted under thermophilic conditions with progressively increasing organic loading rates (OLR). Optimal conditions for fermentation were determined based on the efficiency of hydrolysis and the concentrations of sCOD and volatile fatty acids (VFAs) as follows: at an OLR of 40.48 ± 0.77 g COD/L·d with 1.5 days of solid retention time (SRT), 14.68 ± 0.59% of efficiency of hydrolysis, 14.42 ± 0.30 g sCOD/L and 7.85 ± 0.18 g COD/L of VFAs. Analysis of the microbial community in the anaerobic fermentation reactor revealed that degradation of sewage sludge might be potentially affected by proteolytic microorganisms producing VFAs from proteinaceous materials. Sludge-fermentate (SF) retrieved from the anaerobic fermentation reactor was used as the external C-source for denitrification testing. The specific nitrate removal rate (K ) of the SF-added condition was 7.54 mg NO /g VSS·hr, which was 5.42 and 2.43 times higher than that of raw landfill leachate (LL) and a methanol-added condition, respectively. In the N O emission test, the liquid phase N O (N O- ) of 20.15 mg N/L was emitted as N O of 19.64 ppmv under only LL-added condition. On the other hand, SF led to the specific N O reduction rate (K ) of 6.70 mg N/g VSS hr, resulting in mitigation of 1.72 times the N O emission compared to under the only-LL-added condition. The present study revealed that N O emissions from biological landfill leachate treatment plants can be attenuated by simultaneous reduction of NO and N O during enhanced denitrification via a stable supply of an external C-source retrieved from anaerobically fermented organic waste.