Study On The Removal Of Low-Concentration Ammonia Nitrogen In Sewage By Adsorption-Magnesium Ammonium Phosphate Crystalline Coupling Method

At present,low concentration ammonia nitrogen sewage comes from a wide range of sources,and the discharge is large,if it cannot be effectively treated and causes a large amount of discharge,on the one hand,it will lead to serious water pollution,on the other hand,it will also cause the loss of ammonia nitrogen resources.As an effective method for removing and recycling ammonia nitrogen from sewage,magnesium ammonium phosphate crystallization method is widely used in the research of ammonia nitrogen sewage treatment,but one of the necessary conditions for the removal of ammonia nitrogen by this method is that it must have a high concentration of reactants to effectively form magnesium ammonium phosphate crystals,and the effect of sewage treatment with low ammonia nitrogen concentration is poor.Therefore,this paper explores the method of adsorption-magnesium ammonium phosphate crystalline coupling,and systematically studies the removal effect of coupling process on low-concentration ammonia nitrogen in sewage by using the simulated low-concentration ammonia nitrogen effluent as the experimental object,and the main conclusions obtained in this study are the main conclusions as follows:In this paper,activated clay（AC）,magnesium chloride and sodium hydroxide were used as raw materials,under the conditions of n(Mg²⁺):n（OH^-）ratio of 0.25,0.5,0.75and 1.0,the active clay was wet modified,and the collected impregnates were modified at 400°C.Four magnesium-loaded composites AC-Mg_0.25,AC-Mg_0.5,AC-Mg_0.75 and AC-Mg_1.0.The ammonia nitrogen adsorption experiment,magnesium oxide load analysis,SEM,XRD,BET,zeta potential and cation exchange capacity analysis were carried out on the prepared magnesium carrying composite material and AC.According to the experimental results,the magnesium oxide loads of AC-Mg_0.25,AC-Mg_0.5,AC-Mg_0.75 and AC-Mg_1.0 are 0.49%,0.88%,1.02%and 1.16%,respectively.The adsorption effects of ammonia nitrogen at a concentration of 50 mg/L are 10.3,11.8,8.6 and 5.3mg/g,respectively,which are significantly improved compared with AC adsorption capacity of 3.3 mg/g,and it can be seen that AC-Mg_0.5 has the best adsorption effect on ammonia nitrogen.XRD shows that the space group of the loaded Mg O is Fm-3m（225）,which belongs to face-centered cubic structure.Compared with AC modified MG-carrying composites,the specific surface area decreased significantly and the proportion of mesoporous pore volume increased significantly.The zeta potential on the surface of the four Mg-carrying active clay soils increased with the increase of n(Mg²⁺):n（OH^-）ratio,and the cation exchange capacity was consistent with the adsorption capacity.The removal process of ammonia nitrogen conforms to the quasi-second-order kinetic model（R²>0.98）,and the adsorption isotherm conforms to the Langmuir model.Therefore,the removal of ammonia nitrogen by active clay before and after modification is mainly chemisorption,and the adsorption of ammonia nitrogen is mainly monolayer adsorption.Using AC-Mg_0.5 as adsorbent,the adsorption-ammonium magnesium phosphate crystallization coupling process was constructed by adding a phosphorus source（Na H₂PO₄）.Under the conditions of ammonia nitrogen mass concentrations of 30,50and 70 mg/L,respectively,the removal equilibrium could be reached after 240 min,and the adsorption capacity of ammonia nitrogen in this process was 0.97 times,1.85 times and 1.59 times higher than that of AC-Mg_0.5 for ammonia nitrogen direct adsorption removal,respectively.The characterization analysis of FTIR,XRD,SEM and particle size of the recovered products of the experiment showed that the removal mechanism of low-concentration ammonia nitrogen by adsorption-magnesium ammonium phosphate crystallization coupling process was as follows:first,AC-Mg_0.5 The efficient adsorption of ammonia nitrogen and phosphorus gathers the two in a tiny area on its surface,so that ammonia nitrogen and phosphorus reach a high concentration state in the surface micro area,and the reactant concentration reaches the reactive conditions of ammonium magnesium phosphate crystallization,so as to realize the removal and resource recovery of low concentration ammonia nitrogen,and it can be seen from the experimental results that the process can effectively treat low concentration ammonia nitrogen in sewage.The removal of low concentrations of ammonia nitrogen by AC-Mg_0.5 in the process conforms to the quasi-secondary kinetic model,which is subject to the combined action of surface diffusion and internal diffusion,and the adsorption process of ammonia nitrogen conforms to the Langmuir isothermal adsorption model,AC-Mg_0.5 at 25°C under the conditions of no phosphorus source and phosphorus source,the maximum adsorption capacity of ammonia nitrogen was 37.05 mg/g and 83.47 mg/g,respectively.It shows that the reaction of ammonia nitrogen to generate magnesium ammonium phosphate crystals is the main reason for improving the removal effect of ammonia nitrogen,and the removal process of ammonia nitrogen by the process is a spontaneous endothermic reaction.The optimal phosphorus source dosage,AC-Mg_0.5 dosage,initial p H and reaction temperature of solution,and the effects of coexisting cations(K⁺,Ca²⁺)in the solution on the coupling process were explored.The experimental results show that the optimal dosage of the phosphorus source is 1:1 in the mass concentration ratio of ammonia nitrogen and phosphorus in the solution,the optimal dosage of AC-Mg_0.5 is 2.0 g/L,and the process reaction is the best when the initial p H of the solution 9,at a temperature of25°C,the removal effect of ammonia nitrogen can reach 87.3%,which is the best ammonia nitrogen removal effect in this process.K⁺and Ca²⁺in solution had obvious effects on the removal and recovery of low concentrations of ammonia nitrogen by adsorption-magnesium ammonium phosphate crystallization coupling method,and with the increase of K⁺and Ca²⁺concentrations in solution,The removal effect of ammonia nitrogen is decreasing,and according to the XRD characterization results of the recovered products,the magnesium ammonium phosphate crystals produced by the reaction are also decreasing.Figure[32]Table[12]References[101]...