| N2O is one of the main greenhouse gases in the troposphere, destroying the ozone layer, forming acid rain.it is one of the most important greenhouse gases after CO2 and CH4, effecting on the global climate and ecological environment more and more serious, until now this problem caused widespread concern around the world. The sewage treatment process, especially the sewage treatment plants using biological nitrogen removal process, is one of the most important anthropogenic source of the N2 O release. With the acceleration of urbanization, emissions and improvement of the efficiency of sewage treatment will continue to increase N2 O emission.So there is an urgent need to study the emission characteristics of N2 O during biological nitrogen removal process and the measurs of reduction control. In view of the current study of N2 O emission during sewage treatment process is to be concentrated in the activated sludge system and the N2 O generating mechanism and influence factors in biological membrane system have little reported. This study used biological aerated filter process, investigating the effects of N2 O emission during sewage treatment process under different dissolved oxygen, hydraulic retention time and the ratio of carbon and nitrogen,it has important significance on the implementation of N2 O reduction control in biological membrane method in the future.Based on the traditional biological aerated filter equipment, through the single factor experiment, study the effects of dissolved oxygen, hydraulic retention time, carbon and nitrogen ratio on the performance of sewage treatment equipment in order, at the same time, monitor the release of N2 O from biofilter aerobic zone and anoxic zone,analysis effect of N2 O release under different conditions in biological nitrogen removal process with the pollutant removal, finally the better condition which not only guarantee the good removal efficiency, but also can make the minimum N2 O emission would be found.Equipment hanged film by inoculating activated sludge aeration and then cultured film with lowcontinuous influent flow, media using ceramsite with large specific surface area.After about 20 days’ operation,NH4+-N and COD removal rate were stable at more than 65% and 80% respectively, the effluent concentration of them around 15mg/l and below, 50 mg /l, indicating basically completionof the film hangingand start-up phase.Operate equipment stably in HRT of 6h, the C/N about 10:1, DO respectively of 2mg/ l, 4mg/l, 6mg/l. COD removal mainly occurred in the nitrification process and the effluent COD removal rates all can reach about 90%,which shows that the DO changes had little effect on the removal of COD; NH4+-N removal also mainly occurs in the nitrification process, and there were significant differences among it. When DO was 6mg/l,the highest removal rate of 92.1% was reached, so the higher DO concenteation was propitious tothe removal efficiency of NH4+-N; the average removal rates of TN in nitrification were a little low, and through denitrification, removal rate of TN reached 46%, 56.8%, 53.3% respectively, it proved that the appropriate increase of DO can improve the removal rate of TN, but DO is too high, nitrification completely,denitrification inhibited, resulting in the decrease of TN removal.At the same time, when DO was 2mg/l, 4mg/l, 6mg/l, release of N2 O every day in nitrification stage were 11.856mg/d, 4.024mg/d, 2.944mg/d respectively, higher DO concentration, more complete nitrification, weaker aerobic simultaneous denitrification and denitrification of nitrifying bacteria can reduce N2 O release; In denitrification stage, N2 O release were 1.480mg/d, 2.674mg/d, 4.756mg/d every day. Because N2 O reductase activity was inhibited in the denitrification process with higher DO, the release of N2 O was also promoted. Integrated nitrification and denitrification process, when the DO was 4mg/l, the amount of N2 O produced a minimum of 6.698 mg/d.Operate BAF stably with DO of 4mg/l, C/N about5:1, HRT of 4h, 6h, 8h respectively.The COD removal ratewas all above 87%, as long as there was adequate DO concentration, HRT had less effect on COD removal; The average removal rate of NH4+-N in HRT of 6h and 8h were 92.1% and 91.5%; after complete nitrification and denitrification process,the removal rate of TN reached the maximum of 56.5% in HRT of 6h and increace of HRT in a certain range was conducive to the removal of TN. When HRT was 4h, 6h, 8h,the quantity of N2 O release everyday was 5.400mg/d, 2.416mg/d and 2.712mg/d respectively in nitrification stage.Shorter HRT can increase the organic load inhibit activity of nitrite oxidizing bacteria,resulting in the accumulation of nitrite promoting the release of N2O;in denitrification stage releases of N2 O every day was 0.354mg/d, 0.660mg/d and 0.759mg/d. When HRT was 4h, the release rate of N2 O was the smallest.Too long HRT reduced COD concentration of aerobic effluent and the inadequate carbon flowing to anoxic stage, denitrification was not complete, promoting the release of N2 O. Integrated nitrification and denitrification process, when the HRT was 6h, the amountof N2 O release was the least only 3.076 mg/d, while meeting good pollutant removal efficiency.When the equipment operated stably under condition of DO of 4mg/l, HRT in 6h, C/N about 2, 5, 8 respectly, the average removal rate of COD were71.2%, 90.6% and 90.8%, in order to ensure good COD removal, C/N should be controlled not less than 5; the removal of NH4+-N has the same trend, when C/N was 5, the removal rate of NH4+-N had the highest one of 91%; After the denitrification, removal rate of TN was significantly increased.When C/N was 5, TN had thehighest removal rate of 56.8%. Production of N2 O during the nitrification process every day was 5.776 mg/d,3.187mg/d and 4.700mg/d,while during denitrification process was 0.282mg/d,0.223mg/d and 0.190mg/d, adding N2 O released from nitrification and denitrification showed that C/N of 5 can maintain the equipment in good treatment effect, also minimize the release of N2O... |
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