The Characteristics Of N₂O And NO Productions And Emissions During An Anaerobic/aerobic/anoxic Sequencing Batch Reactor Treating Nitrogen-containing Wastewater

The activated sludge method is the most commonly used technology in the municipal wastewater treatment plants?WWPTs?,the sequencing batch reactor?SBR?which worked under the mode of anaerobic/aerobic/anoxic?An/O/A?has emerged as a promising process,due to its high nutrient removal efficiency and low energy consumption.However,the nitrous oxide?N₂O?and nitric oxide?NO?would be produced and emissied during biological nitrogen removal via this process.N₂O is one of the most imprant greenhouse gases,it contributes to the destruction of the ozone layer and causes the acid rain pollution.NO was one of toxic gases,it is also the precursor of N₂O during the process of denitrification.NO plays an impotant role not only in environment but also in WWTPs.Therefore,it's very necessary to study the mechanisms of biological nitrogen removal and characteristics of N ₂O emission from the An/O/A-SBR process.In this paper,a laboratory scale An/O/A-SBR was used to investigate the productions and emissions of N₂O and NO during shortened nitrification process under different ammonia nitrogen concentrations.It was explored that the effect of ammonia on N₂O emission during nitrite denitrification with intracellular storage as electron donors.And the characteristics of N₂O and NO productions and emissions during anaerobic/anoxic were investigated under different influent COD/N ratios?from 1 to 10?.And the microbial community structures were related to N₂O and NO productions which were successfully tracked under different carbon source.The main conclusions are as follows:?1?The SBR operated steadily in An/O/A model was changed regularly to aerobic process.Results showed that N₂O productions and emissions increased with the rise of influent NH₄⁺concentration.There were 4.65 mg/L,26.73 mg/L,81.26 mg/L productions at the influent NH₄⁺concentrations of 24,96,240 mg/L,respectively.And the N₂O emission factors were 19.3%,27.8%and 33.8%with the NH₄⁺concentration of 24 mg/L,96 mg/L and 240 mg/L,respectively.?2?A SBR activated sludge process operated steadily in An/O/Amodel was switched regularly to An/Amodel the resulte showed that the denitrification duration and the N₂O emission were promoted with the increase of ammonia's concerntration.The reason may be that the free ammonia has a modest inhibitory on the activity of denitrification'microbe.With the increase of the concentration of ammonia nitrogen,the free ammonia as well as the inhibition was increased.At the same time,when the concentration of NO ₂^--N was close to zero,the N₂O reduction was able to take place with intracellular storage as electrons donors,which showed that the existence ofnitrite inhibited the N₂O reduction,and the concentration of inhibition was very low.?3?A single sequencing batch reactor?SBR?with activated sludge running steadily in anaerobic/aerobic/anoxic?An/O/A?was switched aperiodically to anaerobic/anoxic?An/A?mode.The nitric oxide?NO?and nitrous oxide?N₂O?productions during nitrite denitrification of An/A were investigated.The results showed that the NO and N₂O in liquid-phase was accumulated quickly at the beginning of the anoxic period once nitrite was fed.As the NO concentration increased,its toxicity inhibited the reductions of nitrite and NO.Based on the features of cures of NO and N₂O and high-throughput analysis for microbial community structure,two kinds of bacteria were speculated responsible for this process-one was quickly reaction with nitrite and sensitive to the NO toxicity might lead to the accumulations of NO and N₂O,the other one was normal reaction with nitrite and tolerant to NO toxicity might eliminate NO by reducing it directively to N₂.The two bacteria genus might be Ignavibacteriae Melioribacter?10.28%?and Proteobacteria Azospira?4.87%?.The research also confirmed that pH was reduced during reduction of N₂O when the intracellular polymer was served as electron donors.?4?Based on the analysis of High-throughput analysis,comparing to the changes of microbial structure under different carbon source.Result showed:The dominant phylum in the microbial community is still Proteobacteria,but the ratio of the phylum under the glucose as carbon source is significantly higher than the operating conditions of the sodium acetate as the carbon source.But the dominant genus of bacteria is changed to the genus of Sarccharibacteria_genera_incertae_sedis from the genus of Thauera.Compared to the different carbon source,it may be the genus of Melioribacter which led to NO and N₂O production and emission for its sensitive.Azospira and Dechloromonas are tolerance to NO toxicity,and it can eliminate the toxicty and reduction of NO.