Study On Nitrous Oxide Emission And Variation Of Enzymes Activity In Activated Sludge During Biological Nitrogen Removal

Nitrous oxide (N2O) emission from biological wastewater treatment system isconsidered to be one of the main sources for the contributions of greenhouse gas. It isvery important to minimize the emission of N2O in removal of nitrogen and ensure thethe removal efficiency at the same time. It is not entirely clear how to control theemission of N2O. N2O is produced in both nitrification and denitrification process.Dissolved oxygen (DO) has a significant effect on nitrification, but the relationship ofDO on enzyme activity and N2O produced is still a lack of research.Laboratory scale anoxic-aerobic sequencing batch reactor(A/O SBR）was used toinvestigate the production of N2O and variation of hydroxylamine oxidase (HAO) activityin activated sludge under different aeration rates.The results drawn from the study are as follows:(1)Under three aeration rates, SV is between20~30%and SVI at52.9~70.3. Theaverage particle size of the sludge is80.02~95.38um.When aeration ratio were kept at0.6,0.8and1.0L/min respectively, the TNremoval efficiencies in a typical cycle are67.8%,66.0%and45.9%; and ammoniaremoval efficiency are97.1%,98.9%and100%respectively.(2)Extraction of HAO should adopt the method of mechanical grinding combiningwith chemical cleavage, when the concentration ratio of electron acceptor-potassiumferricyanide and electron donor-hydroxylamine in enzyme reaction is1:1,the reactionterminating agent is2mol/L HCL solution, it can obtain a higher enzyme activity. Asthe aeration rate is increased, intracellular DNAand total protein content are improved.(3)Nitrification and denitrification are stages of N2O production. The total N2O (4)emissions continue to reduce with aeration rate increase, are2.747,1.033and1.006mg respectively.(5)At0.6L/min of aeration rate, DO concentration was around0.2～0.35mg/Lthroughout the aerobic phase. Aerobic period of HAO activity rose at the beginning,then reduced, N2O emission rate showed a trend of instead. The major source of N2Oemission during oxic phase is from simultaneous denitrification and nitroxyl doublemolecular polymerization.At0.8and1.0L/min of aeration, DO concentration reached two “DO roof”, firstappeared in0.3~0.5mg/L, respectively, in the second about6.82,7.23mg/L.0.8L/min, HAO activity is positively correlated with N2O emission rate changes.Denitrification is considered playing an important role of N2O emission. In the case of1.0L/min of aeration, HAO activity has a opposite trend with N2O emission ratechanges, and N2O is considered as the result of the interaction of the direct oxidation ofhydroxylamine and denitrification.On the whole, in three kinds of SBR operation mode, only the presence ofhydroxylamine in anoxic period the emission of N2O is the result of HAO action.The results obtained from the research as follows:(1)Different aeration rate resulted in different concentration levels of DO, HAO enzymecan be involved in the oxidation of N2O through different pathways. HAO can generateN2O through direct oxidation of hydroxylamine and produce NO2-by the oxidation ofNH2OH, then product N2O. HAO catalyze hydroxylamine mainly depends on theelectron acceptor type (O2, NO2-)(2)Aeration has a great influence on the removal of pollutants. In the experimental range,with the decrease of aeration, the system of total nitrogen and COD removal increase,but the emission of N2O increased obviously. Therefore, reasonable control of aerationand aeration time, not only can save energy, but also prevent from the dissolution ofN2O.