The Effects Of Operational Parameters On The Denitrification Performance And N₂O Emission In An Oxidation Ditch

Oxidation ditch reactor has been widely used in wastewater treatment plants due to its excellent denitrification performance,low energy consumption and occupation area saving.Operational parameters such as sludge retention time(SRT),hydraulic retention time(HRT),nitrogen to carbon ratio(C/N)in influent and aeration value(AV)have a significant effect on the effluent quality of wastewater treatment plant.In recent years,nitrous oxide(N2O)has attracted extensive attention due to its significant greenhouse effect,and the biological nitrogen removal process of sewage treatment plants was confirmed to be an important source of N2O generation.This study systematically explored the effects of SRT/HRT and ’C/N ratio’/AV on the effluent water quality and the N2O emission in a pilot oxidation ditch.The study confirmed that the effluent water quality was higher and the total N2O emission load was much lower when the oxidation ditch system was operated at longer SRT and higher C/N conditions.In the shock experiments,it was found that running under higher SRT and C/N conditions could effectively improve the resistance ability of the oxidation ditch reactor to the abnormal operational conditions including ammonia overload shock and aeration failure shock.The effluent quality was more stable and the N2O emission rate was less affected by the shock.Batch experiment results indicated that nitrification denitrification was the main process of N2O production,since ammonia-oxidizing bacteria would use excessive nitrite nitrogen as electron donor under the oxygen-limited conditions,resulting in the increase of N2O gas emission.Activated sludge microbial community analysis showed the relative abundance of denitrification bacteria in SRT 25d sludge was much higher and PICRUSt results confirmed that more active nitrite reductase and N2O reductase were found in longer SRT sludge.Therefore,SRT and C/N could be appropriately extended to reduce N2O emission in the biological nitrogen removal process and improve the resistance ability of the oxidation ditch system which contributed for the realization of stable effluent quality and N2O emission reduction.