Study On The Adsorption Kinetics Of Ammonia Nitrogen And Nitrite Nitrogen By Extracellular Polymeric Substance Of Anaerobic Ammonium Oxidation Bacteria

Anaerobic ammonium oxidation(Anammox)has the great advantage of enabling the simultaneous treatment of ammonia nitrogen and nitrite nitrogen in water treatment.However,there is no clear conclusion about the effect of extracellular polymeric substances(EPS)secreted by anammox bacteria on this reaction and bacterial growth.The purpose of this dissertation was to investigate the adsorption and desorption effect of EPS from anammox bacterial on different substrates and the possible role of EPS in bacterial growth.Firstly,according to the dialysis principle,the detection model of EPS adsorbing substrate was established,and the adsorption capacity of ammonia nitrogen and nitrite nitrogen was calculated by this model.The dialysis curves of ammonia nitrogen and nitrite nitrogen were measured using various substrate concentrations and the dialysis k value of ammonia nitrogen and nitrite nitrogen with a fixed substrate concentration was calculated,which were 0.16157 for ammonia nitrogen and 0.08154 for nitrite nitrogen,respectively.In addition,substrate mixtures for the EPS adsorption experiments were diluted with concentrated ammonia or nitrite nitrogen solution.By combining the results from FTIR group detection and proteomic analysis of the EPS,EPS proteins showed to be positively charged,and were found to exist both inside and outside of the bacterial cells.Secondly,the adsorption isothermal experiments showed that EPS had a significant difference with respect to the optimal adsorption capacity and adsorption mechanism of the two substrates.There was no interaction between the factors in the orthogonal experiment,and changing the temperature of the experimental setup did not affect the adsorption of ammonia nitrogen and nitrite nitrogen by the EPS.The average content of adsorbed nitrite nitrogen by EPS was 7.5 times than that of adsorbed ammonia nitrogen.The Freundlich model was used to describe the adsorption of nitrite nitrogen by EPS proteins,but its hypothetical assumption of multiple adsorption sites was not suitable for fully describing the mechanism of ammonia nitrogen adsorption.The Langmuir model was used to fit the maximum adsorption concentration of ammonia nitrogen by EPS,which was quite different from the experimental measurements.In contrast,the adsorption of nitrite nitrogen by EPS was well fitted by this model,with relatively high maximum adsorption concentrations.The positively electrical charge of EPS proteins indicated that EPS had different adsorption characteristics with respect to ammonia nitrogen and nitrite nitrogen.It was difficult to find out how all component of EPS adsorbed substrates.Thus,a theoretical expression was proposed to calculate the ratio of the concentration of adsorbable ammonia nitrogen or nitrite nitrogen in one component of EPS to the total concentration of adsorbable groups and adsorbable structural sites in EPS.Thirdly,the EPS desorption of ammonia nitrogen and nitrite nitrogen shows different rules.The calculation model of EPS desorption was established and the desorption experiments were carried out on the substrate adsorbed by the EPS.Ammonia nitrogen adsorbed by the EPS could be completely desorbed.Nitrite nitrogen adsorbed by the EPS could be completely desorbed when the concentration of nitrite nitrogen was low;when concentrations were higher,approximately half of the nitrite nitrogen could be desorbed indicating a more stable electrical combination with the EPS.The equilibrium constants of the EPS that adsorbed and desorbed the substrates were calculated,which indicated that althouth the adsorption mechanism of ammonia nitrogen and nitrite nitrogen was different,the EPS tended to adsorb both ammonia nitrogen and nitrite nitrogen.At the same time,the amount of adsorption,desorption,and addition by EPS was described in the form of a formula based on the preservation concentration of pre-unit EPS,termed ‘p’,indicating that the higher the content of EPS,the more the substrate retained in the EPS layer.In addition,based on the material diffusion model,the distribution of the substrates in EPS was described and the calculation formulas of various adsorption modes of EPS were deduced.Irrespective of the manner in which EPS layers adsorbed the substrate,the transfer of the substrate through EPSs to the bacterial cell represents the mass transfer process.Lastly,throuth the study of the adsorption and desorption mechanism,combining the quantity of the two substrates adsorbable and desorbable by EPS,it was revealed that EPS had a dual effect on anammox bacteria under natural conditions,acting as a barrier to ammonia nitrogen and a collector to nitrite nitrogen.This dual function enables the widespread distribution of anammox bacteria in nature.