| Along with the rapid development of society and the constant improvement of economy in the world,greenhouse effect and energy crisis have become more and more serious. Nitrous oxide(N2O) is a kind of greenhouse gas which has a great influence on the global warming. And it is also a powerful oxidant in combustion reactions, which can improve the output power of biogas power generation. It is generally known that the amount of N2 O emitted from wastewater treatment is an important part of the total global emissions of N2 O. So it is of great significance for environment protection and energy recycling to investigate the emission of N2 O. In this study, a sequencing batch reactor(SBR) with shortcut nitritation was used to investigate the N2 O release characteristics and the influences of aeration rate on N2 O emission from water to air. In addition, an operating mode of anaerobic/oxic/anoxic(A/O/A) was used to test the potential of recovering N2 O from synthetic wastewater containing ammonia and glucose. Effect of different C/N on N2 O emission was studied also. The main research conclusions are as follows:(1) The appropriate concentration of ammonia and low aeration rate were adopted to achieve a fast start of short-cut nitrification and denitrification processes. After about 28 days of acclimation, ammonia removal rate and nitrite accumulation rate of the SBR reactor reached 95% and the system run stably. With the increase of operating cycle, the ammonia-oxidizing bacteria(AOB) multiplied rapidly, which advanced the ammonia oxidation end-time from 4 hours to 2 hours.(2)The effect of aeration rates(20L·h-1,40L·h-1,60L·h-1and 80L·h-1) on the emission rate of dissolved N2 O was investigated. The results showed that the emission rate of dissolved N2 O was positively correlated with the aeration rate and the dissolved N2 O concentration. When the aeration rate increased from 20 to 80L·h-1, the variation factors of N2 O release rate was 0.0015s-1, 0.0024s-1, 0.0035s-1 and 0.0043s-1.(3)The corresponding emission and production of N2 O in nitritation process were investigated using sequencing batch reactor tests in the open space. It was found that the concentration of dissolved N2 O increased firstly and then decreased during the nitritation process under all of the four aeration rates. The N2 O production decreased as the increase of aeration rate. With the aeration rate increasing from 20 to 80 L·h-1, the ammonia oxidation rate was 99.6%, 94.9%, 92.2% and 85.5%, respectively, and the corresponding N2 O production was 21.3mg·L-1, 9.4mg·L-1, 6.8mg·L-1, 3.7mg·L-1. The total emission amount of N2 O under 20L·h-1 was much higher than that of 80L·h-1. Moreover, the moderate aeration rates(40L·h-1,60L·h-1) was capable to maintain an efficient ammonia oxidation rate as well as an acceptant N2 O emission.(4) To investigate the role of heterotrophic denitritation in N2 O production, several tests had been devised at the key points during the nitritation process. This finding demonstrates that the function of heterotrophic denitritation in N2 O production in the nitritation reactor is considerable, especially under lower DO concentrations and exhaustion of the available organic carbon. Meanwhile, when the operating mode of the single SBR was A/O/A, the majority of the nitrite transformed from ammonia nitrogen during nitritation process could be converted into N2 O in the later anoxic period by PHB heterotrophic denitritation with a conversion rate of 77%. Furthermore, several different COD/N ratios were selected to investigate their effects on N2 O production by heterotrophic denitritation in the later anoxic phase of the A/O/A SBR. The results indicate that COD/ N was greater than 2.2 in the influent might be necessary for completely denitrifying nitrite to N2 O in the later anoxic phase. As a result, the A/O/A SBR presents potential ability to produce and recover N2 O from wastewater containing ammonia and organic carbon. |
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