The Effect Of Fe³⁺ On Greenhouse Gases Emission In Simultaneous Nitrification And Denitrification Process

At present, Global warming has become the focus of the international community at present. N2O, CH4and CO2is acknowledged as the three most important greenhouse gases which accounted for nearly80%of the greenhouse effect. Biological treatment of wastewater is considered to be the important source of greenhouse gases. Simultaneous nitrification and denitrification process is a new kind of biological nitrogen removal process, which has advantages of low energy consumption and good treantment effect, so it get more and more attention. Iron, which exists in cytochrome and ferredoxin, is the carrier of redox reaction and the cofactor of some enzymes (decarboxylase and so on). In addition, it is also the participants of electron transport chain, and has important impacts on the microbial metabolism. Therefore, in this article using iron as the character element, anaerobic-aerobic SBR reactor, has a research about greenhouse gas emission when different concentrations of Fe3+is added to the stimultaneous nitrification and denitrification reactors. The main research conclusions are as follows:(1) Low concentration of Fe3+has improved the ability of removing COD, nitrification and denitrification capacity in simultaneous nitrification and denitrification process. However, high concentration of Fe3+has inhibited ability of removing COD, nitrification and denitrification capacity in simultaneous nitrification and denitrification process. On the condition of five different concentrations of Fe3+, the removal rate of TP is increasing with addition of Fe3+in five reactors.(2) Low concentration of Fe+has less effect on emission rate and quantity of N2O and decreases a little. However, high concentration of Fe3+has promoted N2O emission in stuminilaneous nitrification and denitrification SBR reactors. On the condition of five different concentrations of Fe3+, the emission rates of CH4and CO2are similar, the removal rate of TP is increasing with addition of Fe3+in five reactors. The quantities of CH4and CO2are also similar in five reactors. (3) For five systems, the greenhouse effect is caused by CO2and N2O rather than CH4that has a low concentration. Both of CO2and N2O are greatly released at the aerobic stage. During a typical cycle period, the released greenhouse gas is10209.8,9970.9,8677.8,11593.2, and14606.1mg for1#,2#,3#,4#, and5#reactors, respectively. Comparing to the blank reactor (1#), the greenhouse effect is decreased by4.30%for2#reactor and by15.01%for3#reactor, while it is increased by13.55%and43.06%for4#and5#reactors, respectively. These results indicate the addition of a small mount of Fe3+enhances the nitrification and denitrification reactions, as a result, the removal rate of TN is increased and the greenhouse effect is weakened. However, at the high concentration of Fe3+, the activity of microorganism is inhibited and the removal rate of pollutant declines, exhibiting a relatively significant greenhouse effect.(4) At the concentration lower than40mg/L, Fe3+has a positive effect on the activity of dehydrogenases and electron transfer system in activated sludge, with a highest effect at20mg/L. In contrast, at concentration of60mg/L, the activity of the dehydrogenases and electron transfers begin to decrease, corresponding to an inhibiting effect. Although the accumulation of PHB in organisms can increase the nitrogen removal rate at the late stage of the simultaneous denitrification reaction, it will cause the high release of N2O. The release of N2O can be better examined by OUR than by DO.