Mitigating off-gas emissions in the biological nitrogen removal via nitrite process treating anaerobic effluents

Abstract A sequencing batch reactor treating the reject water produced from the dewatering of the anaerobic co-digestate of waste activated sludge and the organic fraction of municipal solid waste was monitored in order to assess the off-gas emissions that were produced. The gaseous emissions of nitrous oxide (N2O), carbon dioxide (CO2), methane (CH4), ammonia (NH3) and methyl mercaptan (CH3SH) produced during the biological nitrogen removal via nitrite route were monitored. During experimental period 1 a volumetric nitrogen loading rate (vNLR) of 1.08 kg N/m3 d was applied, while in period 2 the vNLR was 0.81 kg N/m3 d. Nitrous oxide emissions decreased from 1.49% of the influent nitrogen load in period 1 to 0.24% in period 2. The higher dissolved oxygen (DO) concentration and the lower accumulation of nitrite in the reactor resulted in significantly lower nitrous oxide emissions in period 2. Some methane (5.8% of influent COD load) was emitted during period 1, as the lower DO concentration created micro-anaerobic conditions within the sludge flocs