The Effect Of Influent Carbon Nitrogen Ratio On N₂O Emission And Minimization In Biological Nitrogen Removal Process

As the eutrophication increasingly becoming outstanding issue, biological wastewater nitrogen removal technology develops rapidly. However, nitrous oxide (N2O) can also be produced through the nitrogen removal process. It is growing at the rate of0.25%per year. N2O is an important geenhouse gas and its geenhouse effect is310times higher than CO2. It has great impact on global environment and climate. N2O can consume ozone and destroy the ozone layer, and it also can endanger the natural ecosystems and human living foundation. Studies have shown that the biological wastewater treatment is an important man-made source. Therefore, it is very important to study the efficiency of pollutants removal and the release of N2O in wastewater biological nutrient removal system.In this study, the anoxic-oxic SBR biological nitrogen removal system was set up to investingate the impact on pollutant removal efficiency and N2O emission under different influent carbon nitrogen ratio (1.2,3.5,6.8,9.2,12.9). The research studied the relationship between microbial community structure and N2O emission. The results showed that:(1) While the anoxic-aerobic SBR reactor steady running, influent carbon nitrogen ratio has no significant effect on COD removal. However, when the influent carbon nitrogen ratio is less than6.8, the removal rates of ammonia, total nitrogen and total is far below than that of carbon nitrogen ratio greater than6.8.(2) The influent carbon nitrogen ratio has an important effect on N2O emission. When the influent carbon nitrogen ratio is less than6.8, the N2O emission is far less than that of influent carbon nitrogen ratio greater than6.8.(3) No obviously N2O emission during the anoxic phase, while most of the N2O emission occurred during the oxic phase.(4) The relationship between microbial community structure and N2O emission under different influent carbon nitrogen ratio conditions were analyzed by the use of molecular bio-techniques, such as PCR-DGGE. Results showed that the major source of N2O emission was nitrifier denitrification of Nitrosomonas spp during the oxic phase. Different influent carbon nitrogen ratio has a major effect on the community structure of ammonia oxidizing bacteria while no Significant effect on the community structure of denitrifying bacteria.For the reason of relatively low carbon nitrogen ratio in China’s urban sewage, based on the result of carbon nitrogen ratio’s affect on pollutant removal and N2O emission. The pollutant removal efficiency and N2O emssion of sewage biological nitrogen removal system under low influent carbon nitrogen ratio which operated on different conditions (instantaneous-influent A/O SBR system, instantaneous-influent A/O/A/O SBR system, sub-influent A/O/A/O SBR system) was studied. The aim is to achieve the reduction effects of the proposed strategies through maintain pollutant removal with no incresing N2O emssion under low influent carbon nitrogen ratio. The final results show that the instantaneous-influent A/O/A/O SBR system (carbon was sourced) have the best pollutant removal efficiency. The removal rates of COD, ammonia nitrogen, total nitrogen and total phosphorus were:87.91%,94.36%,70.38%and94.51%. The N2O emission was:15.373mg,6.084mg and17.076mg. The N2O conversation rates were:15.51%,5.77%and17.3%. But also, this system has the least N2O emission and conversation rate. The N2O emission and conversation rate is6.084mg and5.77%. So, this operating condition is the reduction effects of the proposed strategie.