| Nitrogen oxide（N2O）emission was calculated by using a mathematical model in Waste Water Treatment Plants（WWTPs）of pulp and paper industry.We used two different ways to calculate N2O emissions in a case study of Sequencing Batch Reactor（SBR）process in a paper mill.Primarily,the method of determining the amount of total nitrogen（TN）was utilized（Model A）.As a comparison,the method of determining the amount of dissolved nitrogen oxide(SN2O)contained by Gas Chromatography（GC）was applied（Model B）.The wastewater samples were collected each batch from the influent and effluent of the SBR system from Guangzhou paper mill.Under the specific conditions in laboratory,the samples were analyzed via two different approaches for the measurement of TN and SN2O.Subsequently,in the Model A,according to the acknowledged previous research of biological nitrogen removal process in WWTPs from pulp and paper industry,the fixed emission factor（EF=0.005 kg N2O/kg TN）of N2O was used to calculate the production of N2O.On the other hand,in the Model B,there is another approach to the N2O emission quantification.Based on the Henry’s law,a mathematical model was established by the relation between the dissolved N2O and N2O emission rate.In this model,the emission factor of N2O was dynamic with the state of influent.The result showed that,via the fixed emission factor and determination of TN concentration in the paper wastewater in Model A,the total N2O emissions were 6 to 35.9 mg/m3/d during the period of case study.And through the exquisite model of Model B,the results showed that the N2O emitted between 4.66 to 5.75 g/m3/d.In addition,the factors affecting N2O emissions during the treatment of paper wastewater were also investigated,including nitrite;dissolved oxygen（DO）;ratio of Chemical oxygen demand for nitrogen（COD/N）;pH;temperature;and the rate of growth of bacteria.Those key operational parameters had effects on the N2O emission.The DO and pH of wastewater had synergistic effects on the N2O accumulation;the pH of wastewater changing in a narrow range（7-8）had slight effects on the N2O emission;the nitrite concentration in the wastewater directly increased the N2O generation in the biological nitrogen removal processes;the COD/N ratio was the indirect-acting factor on the N2O emissions.Thereby,it was found out that factors contributing to N2O emissions in the wastewater treatment process had the interaction effects on each other.Ultimately,the results from Model A was compared with that from Model B under the same conditions in the paper wastewater treatment process.The Model A only concentrates on the TN content and flow rate of influent.By contrast,in the Model B,more influencing factors were taken into consideration like the temperature,bioreactor volume,barometric pressure and some inherent characteristics of the influent wastewater,like the quantity,nitrogen load,diversity of contaminant and so on.Consequently,the emission factors in Model B,were dynamic and was identified more accurate than the fixed emission factor of Model A. |
