Study On Denitrification Removal Efficiency And Nitrogen Fate Of Fe⁰/Fe²⁺ Autotrophic Denitrification

Nitrogen pollution is one of the main causes of water pollution in China.One of the main causes of water degradation is nitrogen pollution.Excessive nitrogen load will increase the eutrophication of water.At the same time,nitrate will be easily reduced to nitrite in the human body,excessive nitrite will lead to cancer.Therefore,wastewater denitrification has been widely concerned by people.How to take effective measures to improve the removal rate of nitrogen from wastewater,so as to reduce the nitrate nitrogen content in water,and improve the water environment is a major issue before us.As the research object,this topic with continuous stirring reactor respectively start Fe0/Fe2+ autotrophic denitrification operation system,and analyses the influence of Fe0/Fe2+autotrophic denitrification denitrification denitrification mechanism,explores the different factors of Fe0/Fe2+autotrophic denitrification efficiency and the effect of and analyses the two different substrates of autotrophic denitrification and the succession of microbial community structure characteristics.The main research conclusions are as follows:The main conclusions are as follows:(1)The reduced iron powder and Feluwere used as the biological denitrification matrix,and the activated sludge was inoculated into the sewage treatment plant.The pH value of the influent was 6.80 and the reaction temperature was 30?,the start-up of Fe0/Fe2+autotrophic denitrification system could be completed in 60 days.During the stable operation of the system,when the concentration of NO3--N in the influent was 55 mg/L and Fe2+ was 575 mg/L,the efficiency of iron(?)autotrophic denitrification was 53.6%,and there was no accumulation of ammonia nitrogen and nitrite nitrogen in the effluent.When HRT was 48 hours and initial influent NO3--N concentration was 25 mg/L,the process of zero valent iron autotrophic biological denitrification was started.The average removal rate of NO3--N was 62.54%in the stable stage.In the reaction results,14.2%of the nitrate nitrogen was converted into nitrite nitrogen and ammonia nitrogen on average,and the rest was converted into gaseous nitrogen.(2)In the iron(?)autotrophic denitrification system,biological reduction played a leading role in denitrification;When the influent Fe/N ratio(The molar ratio of Fe2+/NO3--N)was 3,Fe2+autotrophic denitrification had the best denitrification effect.The maximum nitrate removal rate was 42.12%,and the maximum removal load was 0.051 kg·(m3·d)-1.The optimum pH for iron(?)autotrophic denitrification was 7.The higher or lower the influent pH has a significant effect on the iron(?)autotrophic denitrification.Nitrogen removal efficiency of iron(?)autotrophic denitrification decreased significantly when the concentration of NH4+-N was more than 50 mg·L-1,which disadvantaged the operation of Fe2+autotrophic denitrification.Fe2+autotrophic denitrifying bacteria couldn't promote NH4+-Fe3+reaction.(3)In Fe0 autotrophic denitrification,biological redox played a leading role in denitrification.At the reaction temperature of 30?the Fe0+activated sludge denitrification system showed a better denitrification effect after 24 h.The removal rate of NO3--N was 47.14%,and the concentrations of NO2--N and NH4+-N in the effluent were 5.45 mg/L and 9.32 mg/L,respectively.However,Fe0 and NO3--N did not react under anaerobic conditions in the absence of microorganisms.The operation of zero valent iron autotrophic denitrification and denitrification is optimal when the pH of water intake was 6.The removal rate of NO3--N was 60.12%when the pH of the influent was 6,and the maximum removal load was 0.062 kg·(m3·d)-1.Denitrification of NO2--N also occurred with Fe0 as an electron donor,and both kinds of denitrification were carried out simultaneously in the composite system.However,as the concentration of NO2--N in the composite system increased,the removal efficiency of NO3--N and NO2--N decreased,and the formation rate of NH4+-N also decreased.The reaction rate was the fastest when NH4+-N was not in the influent,and the maximum removal load of NO3--N was 0.064kg(m3·d)-1.With the increase of NH4+-N concentration,the nitrogen removal rate of the composite system gradually decreases,and the formation rate of NO2--N and NH4--N also decreases.(4)There were two types of microorganisms in Fe0/Fe2+autotrophic denitrification,bacteria and fungi,and the higher content of bacteria in the two types of microorganisms had little difference,mainly Proteobacteria,acidobacteria,Actinobacteria,Chloroflexi,and proteobac in Fe0 autotrophic denitrification.The content of teria)was higher than that of Fe2+ autotrophic denitrification.Beta Proteobacteria,actinobacteria and bacteria unclassified were the microorganisms with high content in the autotrophic denitrification of Fe0/Fe2+.There were some differences in the dominant bacteria of Fe0/Fe2+ autotrophic denitrification.The dominant bacteria of Fe0/Fe2+ autotrophic denitrification are Bactria unclassified,GP 10,Gallionella;the dominant bacteria of Fe0 autotrophic denitrification were Bactria unclassified,DERXIA and acidobacteria gp4.