Characteristics Of N₂O Emission During Biological Removal Of Nitrogen From Wastewater

N2O is the major greenhouse gas after CO2 and CH4 in human released greenhouse into the environment, also the most serious material to Ozone depletion in 21 century,causing serious damage to ecosystem. Wastewater treatment is a key source for N2 O emission. With the widely used of biological nitrogen removal, N2 O emission will increase further. Therefore, it has great significance to study the N2 O releasing characteristics and the influence on emission factors in wastewater biological nitrogen removal process, to deal with climate change.This article taken the SBR as the research object, studying the whole denitrification and shortcut denitrification to investigate the N2 O released characteristics and the influences of different C/N and stir velocity on N2 O emission. Besides, external disturbance, such as,wind velocity, stir velocity, and aeration rate also be studied on N2 O emission from water to air. The main research conclusions are as follows:(1) When predicting N2 O emission from water to air, external disturbances(aeration,stir, wind) should be taken into consideration. As a result, aeration, stir and wind all cause theOLa N2 K increased, promoting N2 O emission from water to air, while the influence degree of these three factors on N2 O emission was aeration>stir>wind, this depends on the change of gas and liquid phase.(2) In SBR operation cycle, Setting C/N ratio as 1.5 、 2.5and 5.0 at the whole denitrification and 1.5、2.5and 4.0 at the shortcut denitrification, respectively. When C/N ratio was 2.5:1, N2 O release amount was 0.85 mg and conversion rate was 0.48%during the whole operation cycle while 0.93 mg and 0.6% during the shortcut denitrification. At the same time, the variations of DO and p H were basically consistent with the changes of pollutants concentrations with corresponding relation.(3) C/N ratio was the key control parameters in the whole denitrification operation of sewage treatment. This study used a beaker test to achived C/N ratio influence. Setting C/N ratio as 1.5、2.5、4.0 and 6.0, monitoring N2 O concentration under stirring, finding that N2 O emission increased obviously at a low C/N ratio, due to uncompleteddenitrification with shortage of external carbon source. Thus, it is better to control the C/N ratio higher than 4:1 in whole denitrification, and not less than 3:1 in shortcut denitrification.(4) In addition, stir velocity was also an important fator to N2 O emission. Like the influence of C/N ratio test, monitoring N2 O concentration under different stir velocities,200r/min, 300r/min and 400r/min. Results showed that N2 O emission increased with stir velocity, the release amount of N2 O at 400r/min was 2 and 6.9 times of those at the stir velocity of 300r/min and 200r/min in the whole and shortcut denitrification operation, respectively.