Screening Of Heterotrophic Nitrifying Bacteria In The Beiyun River And Study On Its Nitrogen Removal Efficiency

With the rapid development of the economy and society,human beings produce a large amount of nitrogen-containing wastewater in production and life and discharge it into natural waters.Too high a concentration of ammonia nitrogen can cause eutrophication of water and cause serious damage to aquatic ecosystems and human health.The use of biological methods to remove ammonia nitrogen from water is environmentally friendly,has low processing costs,and has fewer harmful by-products.The traditional biological nitrogen removal process has been widely used in sewage treatment,but has the disadvantages of complicated process,large floor space and low nitrogen removal efficiency.Many types of heterotrophic nitrifying bacteria discovered in recent years have both heterotrophic nitrification and aerobic denitrification,making it possible to carry out nitrification and denitrification simultaneously under the same reaction system and under the same conditions,providing a new theory and approach for biological nitrogen removal.Heterotrophic nitrifying bacteria have the characteristics of rapid growth and reproduction,strongly environmental adaptability,low dissolved oxygen demand,and good ammonia nitrogen removal effect,and play an important role in the biological nitrogen removal process.The screening of heterotrophic nitrifying bacteria and the study of their nitrogen removal characteristics have become the research hotspots in the field of biological nitrogen removal.In recent years,due to the continuous increase of pollutant emissions,the Beiyun River has been seriously polluted,and ammonia nitrogen is the main form of nitrogen pollutants in the water of the Beiyun River.Indigenous microbes have the characteristics of strong adaptability,high efficiency of pollutant removal and low ecological risk in the treatment of water pollution.Screening indigenous heterotrophic nitrifying bacteria from the environment and studying their nitrogen removal characteristics,in order to lay the experimental basis for the treatment of heterotrophic nitrifying bacteria for ammonia nitrogen pollution in water.Therefore,it has important theoretical guiding significance and practical application value.In this study,the indigenous heterotrophic nitrifying bacteria were isolated and screened from the contaminated sediments of the Beiyun River by enrichment culture,gradient dilution plating,plate scribing,qualitative and quantitative experiments,16 strains were isolated by the preliminary screening stage.They were found that 6 of the strains had certain heterotrophic nitrification.Molecular biological identification of a strain of HNM-4 with the best ammonia nitrogen removal effect was carried out,and the strain was identified as Pseudomonas by phylogenetic analysis.The heterotrophic nitrification performance of strain HNM-4 was studied by single factor experiment.The optimum environmental conditions for the heterotrophic nitrification of strain HNM-4were: initial ammonia nitrogen concentration 140 mg/L,and sodium succinate as the best carbon source.C/N of 9~18,the optimum temperature of 30?,the initial pH of 7~8,and the salinity of 0~0.5%.The aerobic denitrification performance of the strain HNM-4showed that within 48 h the removal rate of nitrate nitrogen and total nitrogen by strain HNM-4 was 100% and 12.05%,respectively;when aerobic denitrification was carried out with nitrite nitrogen as the sole nitrogen source,the removal rates of nitrite nitrogen and total nitrogen by HNM-4 for 48 h were 78.64% and 9.75%,respectively.Denitrification experiments show that under the aerobic conditions,the organic compound sodium succinate is used as the carbon source,the strain HNM-4 has both heterotrophic nitrification and aerobic denitrification,which can effectively remove nitrogen pollutants such as ammonia nitrogen,nitrate nitrogen and nitrite nitrogen in water,and the strain also has a certain removal effect on total nitrogen.Finally,bioceramics and polyurethane foam were selected as carriers for immobilization of strains.The selected heterotrophic nitrifying bacteria HNM-4 was adsorbed and immobilized.After several cycles of culture and membrane experiments,the surface state of the carrier before and after the membrane HNM-4 was observed by scanning electron microscopy.It can be seen that the surface of the frame structure of the carrier was covered with a dense layer of milky white bacteria,indicating that the strain HNM-4 has a certain ability to form biofilms.The immobilized strain HNM-4 was added to the simulated ammonia nitrogen wastewater for denitrification experiments.The results showed that the removal rate of ammonia nitrogen and total nitrogen in the simulated wastewater by the immobilized strain HNM-4 was 76.25% and 61.07%,respectively.Compared with the free strain,the immobilization of the strain increased the removal rates of ammonia nitrogen and total nitrogen.It shows that the immobilizedmicrobial technology can strengthen the denitrification effect of indigenous heterotrophic nitrifying bacteria.In this study,we screened indigenous heterotrophic nitrifying bacteria from the sediment of the Beiyun River and studied its nitrogen removal performance and investigated the nitrogen removal efficiency of the immobilized microbial technology to establish a theoretical basis and technical support for the treatment of river ammonia nitrogen pollution.