Preparation And Application Of Microbial Carbon Supported Polymetallic Ozone Catalyst For Ammonia Nitrogen Oxidation

Biological denitrification is one of the most widely used methods to treat ammonia-nitrogen wastewater,but it is extremely susceptible to the influence of water quality,and is limited by such factors as long reaction cycle and harsh reaction conditions.Therefore,the development of ozone-catalyzed ammonia-nitrogen oxidation process independent of biochemical process for nitrification of ammonia-nitrogen oxide and the use of denitrifying bacteria for denitrification treatment will greatly improve the efficiency of ammonia-nitrogen wastewater treatment.In this study,a kind of microbial carbon-supported polymetallic ammonia nitrogen oxidation catalyst was prepared by pyrolysis of microbial residue after adsorption of metal ions.The preparation conditions and reaction conditions were optimized to characterize its structure and reveal its reaction mechanism.Secondly,the ammonia nitrogen wastewater from a rare earth mine in Hunan reaches the first grade discharge standard of Comprehensive Sewage Discharge Standard（GB8978-1996）through the study of catalytic ozone oxidation of ammonia nitrogen combined with biological denitrification.The main conclusions of this paper are as follows:（1）The adsorption of Fe³⁺,Co²⁺,Mn²⁺,Ni²⁺,Ce³⁺and Cu²⁺by microbial slag is monolayer adsorption,and the prepared catalyst containing Co and Fe has better catalytic performance.The adsorption behavior of microbial residue on six metal ions was more consistent with the Langmuir isothermal adsorption model.Under the condition of 20 mg/g metal loading and the maximum metal loading,the Co catalyst supported by microbial carbon had the best catalytic performance,and the oxidation rate of ammonia nitrogen was 59.6%and nitrogen conversion was 14.8%.The catalytic performance of Fe catalyst supported by microbial carbon is slightly lower than that of Co catalyst supported by microbial carbon,but both Fe catalyst and Co catalyst supported by microbial carbon can be magnetically recovered.（2）The catalyst prepared under the optimal preparation conditions is the magnetic microbiological carbon Co Fe catalyst,whose oxidation of ammonia nitrogen is mainly indirect oxidation through·OH.The optimum preparation conditions were as follows:metal loading 50 mg/g,Mass ratio of Fe/Co 1:2,pyrolysis temperature 700℃,pyrolysis time 90 min.The optimal catalytic conditions for the oxidation of ammonia nitrogen by catalytic ozone are as follows:room temperature 25℃,simulated ammonia nitrogen wastewater concentration 50 mg/L,system 500 m L,catalyst dosage 1.0 g/L,air flow 1.5 L/min,ozone concentration 74.6 mg/L,reaction time 2 h.Under these conditions,the oxidation rate of ammonia nitrogen is 70.5%.The conversion rate of nitrogen is 14.8%.Coexisting ion results show that CO₃^2-,HCO₃^-,SO₄^2-can trap·OH and inhibit the reaction,while Br^-can participate in the reaction and promote the reaction by converting ammonia nitrogen into nitrogen.XRD results show that the catalyst is divided into Co Fe alloy,and the position and intensity of absorption peak do not change before and after the reaction.SEM-EDS results show that Fe and Co elements are uniformly loaded on the rough surface and void of the catalyst,and the proportion of Fe and Co elements is 11.81%and 11.15%,respectively.FTIR results showed that·OH and ammonia nitrogen could be adsorbed on the surface of the catalyst.VSM results show that the saturation magnetization of the catalysts are 17.40emu/g and 15.01 emu/g,respectively.（3）The optimum C/N and p H of the selected denitrifying bacteria are10.0 and 8.0,respectively.The combined process can make the ammonia-nitrogen wastewater from a rare earth mine in Hunan discharge up to standard.Under the conditions of initial nitrate nitrogen of 270.6 mg/L,C/N of 10.0 and p H of 8.0,the logarithmic growth period of microbial community was 6-30 h and reached the decline stage 42 h later.After the denitrification system was run for 36 h,nitrate nitrogen could be completely removed,and there was no accumulation of nitrite nitrogen in the solution.After the combined treatment of ammonia nitrogen wastewater from a rare earth mine in Hunan,the concentration of residual ammonia nitrogen is 7.06 mg/L,and the total nitrogen concentration is 7.06mg/L,and there is no accumulation of nitrate nitrogen and nitrite nitrogen in the water,which meets the first-class discharge standard of Integrated Sewage Discharge Standard（GB8978-1996）.To sum up,this study successfully prepared microbial carbon Co Fe catalyst and successfully applied it to catalyze ozonation of ammonia nitrogen,and combined ozonation and biological denitrification process was used to treat ammonia nitrogen wastewater from a rare earth mine in Hunan province to achieve standard discharge,providing a new solution for the treatment of ammonia nitrogen wastewater.