Study On The Adaptability Of DNRA To Different Carbon Sources And Distribution In Natural Environment

With the development of economy,the problem of nitrogen pollution in water is prominent.At present,the sources of nitrate wastewater are extensive,such as industrial wastewater of the steel industry,military manufacturing,nuclear industry and chemical manufacturing.The discharge of nitrate wastewater could cause harm to ecosystems and humans,such as water eutrophication.Unlike Denitrification and Anammox processes,the DNRA(Dissimilatory nitrate reduction to ammonium)process converts nitrate to ammonium and retains nitrogen in the water.The contribution of DNRA process for nitrogen cycle is highly controversial.Therefore,it is necessary to explore the mechanism of DNRA bacteria.In recent years,researches on DNRA were focused on discoveries in various natural ecosystems such as estuaries,wetlands,lakes and oceans.A few laboratory studies on DNRA were carried out.This thesis focused on the research of DNRA bacteria from two aspects.Firstly,the Huangpu River was selected as the research site to investigate the distribution and bacterial structure of DNRA bacteria in natural habitats.Then the enrichment culture of DNRA bacteria was carried out at laboratory on the basis of the Huangpu River research.Three carbon sources of succinate,glucose and ethanol were selected to culture DNRA bacteria.The COD/N was continuously increased during the operation of reactor to realize the successful enrichment culture of DNRA.And the abundance,activity and community structure characteristics of DNRA bacteria were analyzed in this paper.The main results obtained are as follows:(1)DNRA bacteria were commonly found in various natural aquatic ecosystems.DNRA bacteria were found at each site of the Huangpu River,but the abundance and activity of DNRA bacteria were different at each site.DNRA bacteria preferred higher concentration of SOC and ammonium.The potential rate of DNRA was positively correlated with gene abundance(the relationship is not significant)and significantly positively correlated with SOC,which proves that a high organic carbon environmentis more suitable for DNRA bacteria.(2)Based on the preliminary investigation,three carbon sources(succinate,glucose,ethanol)were selected to culture DNRA bacteria in a non-woven membrane bioreactor.The corresponding COD/N at the early,middle and late stages of reactor operation were 6.5,7.7 and 10.0,respectively.It was discovered that the adaptability of DNRA bacteria to COD/N is different.When COD/N=7.7,DNRA bacteria have a stronger competitive advantage,which is conducive to the dominance of DNRA process in reactors(3)The Time and efficiency of successful enrichment culture of DNRA bacteria was different with different reactors when COD/N=7.7.The reactor used ethanol as the carbon source was taken the longest time(100 days)but the highest efficiency of nitrate to ammonium(78.92%).The reactor used glucose as carbon source was taken the shortest time to culture DNRA bacteria(64 days)but the lowest efficiency of nitrate to ammonium(47.63%);The reactor used succinate as carbon source was taken the shortest time(90 days)with the efficiency of nitrate to ammonium(55.65%).It was illustrated that DNRA bacteria prefer to use ethanol with less carbon number as a carbon source rather than succinate and glucose.The reacter used etanhol as carbon source was achieved the better results of DNRA enrichment(4)According to functional gene prediction,it was observed that nitrite reductase,a functional enzyme of DNRA,increased greatly after enrichment.This result showed that the successful enrichment of DNRA bacteria.Based on nrfA functional gene sequencing,the main DNRA bacteria in reactors at phlum level were phyla of Bacteroidetes,Verrucomicrobia and Ignavibacteriae and at genus level were genera of Lentimicrobium,Petrimonas,Melioribacter and Petrimonas.(5)It was different of the community structure of DNRA bacteria between Huangpu River and cultured reactors in my laboratory.Phyla of Proteobacteria,Bacteroidetes and Chloroflexi were the main DNRA bacteria at the Huangpu River.Anaeromyxobacter was the most abundant genus at all sites.(6)The potential rate of DNRA was measured by 15N isotope tracing technology.And the potential rate of DNRA of the laboratory enrichment culture was significantly higher than that of Huangpu River,which proved that the enrichment culture of DNRA bacteria in laboratory was successful.