Studied On Nitrogen Removal Efficiency Of Heterotrophic Nitrification-aerobic Denitrification Of An Achromobacter Denitrificans

Nitrogen compounds in water mainly include organic nitrogen,NH₄⁺-N,NO₃^--N and NO₂^--N,which exist in a single or a variety of mixed forms.However,with the continuous development of industrialization,urbanization and agricultural intensification,the nitrogen balance has long been broken and a large amount of nitrogen has been accumulated in the water environment,and nitrogen pollution has been formed.It is an urgent environmental problem to be solved at present.Biological method is the most widely used nitrogen removal method at the present stage,and the discovery of heterotrophic nitrification and denitrification microorganism provides new ideas and techniques for biological nitrogen removal.This kind of bacteria can not only remove organic matter and nitrogen at the same time,but also complete the nitrification process and denitrification process in a reactor to achieve the real simultaneous nitrification and denitrification.In this study,iron-oxidizing bacteria strain 2-5 with aerobic denitrification capacity was taken as the research object.The 16S rRNA sequence and phylogeny of strain 2-5 were analyzed by molecular biology methods.The ability of ammonification,heterotrophic nitrification and aerobic denitrification of strain 2-5 was investigated.The effect of different nitrogen ratio on the denitrification performance of strain 2-5 and its enhanced SBR reactor was discussed under the condition of the consistency of TN concentration,and the effect of water exchange mode and additional carbon source on the denitrification performance of strain 2-5 enhanced SBR reactor was discussed.The following conclusions are drawn:?1?The 16S rDNA sequence identification and blast homology analysis of strain 2-5 in the laboratory,which was isolated from the biological sponge iron system,showed that the strains 2-5 and Achromobacter denitrificans strain TB 16S rDNA had 99%of the similarity,and the strain 2-5 can be preliminarily identified as Achromobacter denitrificans in the combination of the morphological and physiological characteristics of early strains 2-5.?2?Strain 2-5 could use different forms of nitrogenous compounds to complete the processes of organic nitrogen decomposition,heterotrophic nitrification,aerobic denitrification and simultaneous nitrification and denitrification,and ammoniation.The aerobic denitrification related to the system carbon source,which mainly occurred in logarithmic growth period.The nitrification was carried out in all stages of the strain growth.Strain 2-5 had the best growth performance in organic nitrogen source,which had the most utilization of NO₃^--N.The average removal rate in logarithmic growth period of 12h to 48h is5.68mg/?L?h?.The NO₂^--N existed inhibition to strain growth.The mixed nitrogen source with mixing NH₄⁺-N with NO₂^--N could effectively eliminate the inhibition of NO₂^--N on the growth and metabolism of strains and promote degradation of NO₂^--N.The NO₂^--N removal rate was 99.97%at 48h.Meanwhile,compared with ammonia as the sole nitrogen source system,the removal rate of NH₄⁺-N was also increased by 6.55%when the operation is over.The NH₄⁺-N was beneficial to aerobic denitrification of the strain.?3?Under the conditions of TN concentration of about 1200 mg/L and the C/N ratio remained basically unchanged,the NO₃^--N concentration in raw water was reduced by gradient to increase the concentration of NH₄⁺-N,the heterotrophic nitrification and aerobic denitrification performance of the SBR reactor composed of strain 2-5,strain 2-5+activated sludge,strain 2-5+activated sludge+sponge iron was investigated.The results showed that the increase of NH₄⁺-N concentration in raw water had little effect on the aerobic denitrification performance of different reactors.The three reactors maintained good aerobic denitrification capacity during the whole experiment;In the influent stage of NO₃^--N and NH₄⁺-N at the same time,the reaction conditions with the largest removal of NH₄⁺-N and TN during the cycle are basically concentrated in the NO₃^--N/NH₄⁺-N ratio of 7:4 to 4:7,indicating that the similar concentration of NO₃^--N and NH₄⁺-N in raw water is beneficial to the heterotrophic nitrification and aerobic denitrification ability of strain 2-5 and its enhanced SBR reactor.?4?Under the same conditions of total biomass,strains 2-5 were added to the SBR reactor.The effects of strains 2-5 on the removal of SBR reactors and the changes of concentrations of different pollutants in the cycle were examined through parallel tests.The effect of the water change mode and the external carbon source on nitrogen removal performance of different reactors was also investigated.The results showed that:1)The addition of strain 2-5 enhanced the SBR reactor to increase the average removal of TN by4.06 mg/L.Simultaneously,the addition of strain 2-5 promoted the conversion of NH₄⁺-N in the reactor,and the effect of nitrification was better than the traditional activated sludge reactor;2)Treating equal volume wastewater at the same time,using a small amount of water exchange method can improve the TN removal of SBR reactor and strain 2-5 enhanced SBR reactor,and increase the utilization efficiency of carbon source;3)During the operation cycle,the addition of an inexpensive carbon source can promote the degradation of NO₃^--N and TN in the SBR reactor and strain 2-5 enhanced SBR reactor.This study laid a foundation for the practical application of strain 2-5.