Partial Nitrification-Denitrification Double Sludge System Treating Ammonium-rich Wastewater And Its N₂O Emission

Ammonium-rich wastewater contains high concentrations of ammonium nitrogen（NH₄⁺-N）and relatively low concentrations of organic carbon.When the conventional nitrification-denitrification process is applied to treat the ammonium-rich wastewaters,it requires a high-energy input and results in low nitrogen removal efficiency.Usually,the organic carbon contained cannot satisfy the requirement of denitrification.During partial nitrification process,nitrite-oxidizing bacteria would be inhibited,which results in nitrite nitrogen（NO₂^--N）accumulation,and denitrifiers use NO₂^--N as electron acceptor.Therefore,partial nitrification-denitritation rather than full nitrification-denitrification possesses the following advantages:25% lower oxygen consumption,40% lower external organic carbon requirement,and 63% lower sludge production.In this study,double-sludge sequencing batch reactor（SBR）systems with the high substance gradients were applied to acclimate nitrifiers and denitrifiers seperately,and the properties of partial nitrification and denitritation were studied.Effects of dissolved oxygen（DO）,free ammonia（FA）and free nitrous acid（FNA）on nitrifying activity and nitrous oxide（N₂O）emission were investigated to analyze how to achieve high loading rates and maintain stable and high nitritation efficiencies.Simutaneously,effects of complex organic carbon and FNA on denitrifying property and N₂O production and emission were also studied.Conclusions were obtainded as follows:（1）In the partial nitrification process,the stable and high nitritation efficiencies achieved could be due to the combined effects of DO,FA and FNA.N₂O emission was strongly influenced by FNA,for which the N₂O emission factor was 0.22%-1.10%,while FA have little influence with the N₂O emission factor of 0.22%-0.65%.The genus Nitrosomonas was the main AOB in the activated sludge acclimated by ammonium-rich wastewater（2）In the denitritation process,denitrifying activities and N₂O generation were affected significantly by both organic carbons and FNA with nitrite as the electron acceptor.Especially,an obviously increasing of N₂O production and emission occurred when FNA concentration were above the threshold value.When complex organic carbons（peptone and starch）were use as electron donors,there was little influence of FNA on denitrifying properties.Various denitrifying bacteria species were detected in the activated sludge acclimated by sodium acetate,sodium propiorate,peptone and starch,respectively.The genus Thauera was detected from all SBRs,with the ratio of 19.8%,19.0%,2.6%and 10.7%,respectively.（3）In the partial nitrification-denitritation double-sludge system treating ammonium-rich wastewater,a high nitrogen removal efficiency was achieved with an influent NH₄⁺-N concentration of 1172.74±3.49 mg/L,organic carbon of peptone and starch（1:1）and COD/N ratio of 2,.During the denitritation process,the maximum N₂O emission was 0.078 mg N/L,the N₂O emission factor was 0.88%in the partial nitrification process.（4）During the denitritation process,when peptone and starch were used as organic carbons,due to the difference of metabolic pathways and microbial community structure,denitrifying properties and N₂O emission varied.