Study On Adsorption Performance And Mechanism Of Ammonia Nitrogen By Iron Activated Carbon At Low Temperature

Ammonia nitrogen is one of the main pollution indicators in water,and its excessive content will not only cause damage to the ecological environment,but also endanger human health.At present,the biological treatment method is mainly used to degrade ammonia nitrogen in sewage treatment plants.However,at low temperatures,the growth and reproduction of microorganisms are limited,which makes it difficult to remove ammonia nitrogen.Therefore,it is necessary to find an effective method for removing ammonia nitrogen at low temperature.Activated carbon is a good adsorption material because of its strong adsorption performance and low price,inorder to further improve the adsorption capacity of activated carbon for ammonia nitrogen at low temperature.In this paper,the"impregnation-calcination"method was used to prepare iron loaded activated carbon（Fe-AC）,and a series of characterizations were carried out.Low temperature（10℃）static adsorption experiments and dynamic penetration experiments were also carried out.In winter,a pilot experiment was conducted in the sewage treatment plant in Northeast China.The main research results were as follows:（1）Orthogonal preparation experiment results of Fe-AC prepared by the"impregnation-calcination"method showed that the optimal preparation conditions were:Fe（NO₃）₃impregnating solution concentration of 0.15 mol/L,Na OH impregnating solution concentration of 0.6 mol/L,immersion time 2 h,calcination temperature 300°C and calcination time 2 h.Fe-AC characteristic characterization results showed that the surface became rough after modification of activated carbon,the specific surface area and pore volume of Fe-AC were larger than AC.Iron was mainly loaded on activated carbon in the form of ferric oxide.The zero point was increased from 8.11 to 10.07.The content of basic groups in surface functional groups increased by 13.70%,and the content of acidic groups in surface functional groups decreased by 14.33%.（2）Low temperature（10℃）static adsorption experiment results showed that under the same conditions,the removal effect of Fe-AC on ammonia nitrogen was better than AC.Increasing the amount of activated carbon could increase the removal rate of ammonia nitrogen in water.The equilibrium equilibrium time for the adsorption of ammonia nitrogen by Fe-AC was 240 min.With the increased of the initial concentration of ammonia nitrogen,the adsorption amount of activated carbon on ammonia nitrogen increased.The ammonia nitrogen adsorption effect was the best at p H=7.Among the three ions Na⁺,K⁺and Ca²⁺,the competition between K⁺and NH₄⁺was most obvious.The results of fitting analysis of the isotherm adsorption model showed that both Langmuir and Freundlich isotherm models could better describe the adsorption of ammonia nitrogen by AC and Fe-AC,and the fitting effect of the Temkin model was slightly worse.The fitting analysis of the kinetic model showed that the adsorption process of ammonia nitrogen on AC and Fe-AC was best fitted by the quasi-second-order kinetic model,and the Elovich model also achieved a good fit.The calculation results of thermodynamic function indicated that the adsorption of ammonia nitrogen by AC and Fe-AC was an exothermic process based on physical adsorption.（3）Low temperature（10℃）dynamic penetration experiment results showed that under the same conditions,the Fe-AC filter column was penetrated later than the AC filter column.The correlation models were used to fit dynamic penetration experiment results.The research showed that the BDST model could better describe the dynamic adsorption process of activated carbon to ammonia nitrogen and the Yoon-Nelson model could accurately predict the time required for 50%penetration.（4）The results of a pilot test conducted in the Northeast sewage treatment plant in winter showed that Fe-AC filter had better removal rate of ammonia nitrogen,TP,COD,UV₂₅₄and turbidity in low temperature tail water than AC filter.Under the optimal operating conditions of a filtration speed of 9 m/h,a filter height of 120 cm and no aeration.The effluent quality of the Fe-AC filter met the Class IV water body standards in GB3838-2002 Surface Water Environmental Quality Standards.