GASEOUS EMISSIONS FROM THE BIOLOGICAL VIA NITRITE NITROGEN REMOVAL PROCESS TREATING ANAEROBICALLY CO-DIGESTED EFFLUENTS

In this work the gaseous emissions of nitrous oxide (N2O), carbon dioxide (CO2) methane (CH4), ammonia (NH3) and methyl mercaptan (CH3SH) produced from the nitritation/denitritation biological nutrient removal (BNR) process were determined in a sequencing batch reactor (SBR). The SBR treated the anaerobic supernatant produced from the anaerobic co-digestion of the organic fraction of municipal solid waste (OFMSW) and waste activated sludge (WAS). Two experimental periods were carried out: period 1 in which a volumetric nitrogen loading rate (vNLR) of 0.81 kgN/m3d was applied, using acetic acid as carbon source and period 2 with vNLR=1.09 kgN/m3d using fermentation liquid produced from biowaste as carbon source. N2O emissions were 0.24% and 1.38% of the influent nitrogen load in periods 1 and 2 respectively. The higher dissolved oxygen (DO= 1.5 mg/L) concentration as well as the lower accumulation of nitrite resulted in significantly lower N2O emissions in period 1 compared to 2. NH3 emissions were very low (<1% of influent nitrogen load), while some methane (5.3% of influent load as COD) was emitted during period 2, as the lower DO (0.95 mg/L) concentration probably created micro-anaerobic conditions within the sludge flocs; this was also favoured by the use of fermentation liquid as a carbon source.