| In recent years,with the problem of eutrophication becoming more and more serious,the water quality discharge standards have been gradually improved,and how to control the discharge of ammonia nitrogen in sewage economically and efficiently has becomed a research hotspot in the field of water pollution prevention.Sewage treatment plants in many parts of northern China are operated under low-temperature conditions for a long period of time,which cannot guarantee the efficient removal of ammonia nitrogen by biological processes.Based on the interaction between the enhancement of microorganisms by iron ions and the change of activated carbon morphology and structure by ultrasonic cavitation.In this work,it is proposed that the iron salt was loaded on the activated carbon by ultrasonic impregnation method,and which was used in the biological activated carbon filter for advanced treatment of the tail water of the sewage plant.The iron ion-enhanced biological activated carbon filter for ammonia removal efficiency and microbial characteristics analysis were conducted,the main research results are as follows:The effect of load conditions on adsorption capacity of modified activated carbon was investigated.The results showed that when the concentration of iron nitrate was 0.2 mol/L,the concentration of sodium hydroxide was 1 mol/L,the ultrasonic power was 520 W and the ultrasonic time was 90 min,the adsorption capacity of modified activated carbon to ammonia nitrogen reached the maximum.Iron modified activated carbon（Fe-AC）was prepared by ultrasonic impregnation method,and the optimal preparation conditions were obtained by orthogonal test:the impregnation solution concentration of iron nitrate was0.25 mol/L,the impregnation solution concentration of sodium hydroxide was 0.8 mol/L,the ultrasonic power was 520 W,the ultrasonic time was 105 min.The characteristics of Fe-AC showed that the surface of the modified activated carbon was rougher,the specific surface area was increased by 113.71 m2/g,the total pore volume was increased by 0.25cm3/g,iron was loaded on the activated carbon in the form of Fe2O3,and the Zeta potential decreased from-14.6 mv to-33.4 mv.At low temperature（10℃）,the removal efficiency of Fe-AC and AC filter columns in the biofilm growth and stable operation period was compared.The results showed that Fe-AC and AC filter column had the same removal rules for ammonia nitrogen,NO2--N,NO3--N and COD,and the former had higher removal efficiency for ammonia nitrogen and COD.After stable operation,the ammonia nitrogen removal capacity of Fe-AC filter column was better than that of AC filter column under different operating conditions of temperature,p H value and flow rate,indicating that the ability of microorganisms on the surface of activated carbon to adapt to the environment was improved by Fe ion.SEM of biological activated carbon showed that globular bacteria and short rod bacteria were the main microbial types in the two filtration columns,and the biomass of Fe-BAC was higher than that of BAC.EDS showed that after long-term use of Fe-AC,the iron content of surface load was decreased from 7.7%to 0.39%,which was utilized by microorganisms.The analysis of microbial characteristics of biological activated carbon filter at low temperature（10℃）showed that the microbial quantity,microbial activity,extracellular polysaccharide and extracellular protein contents in Fe-AC filter column were higher than those in AC filter column.The results of high-throughput sequencing showed that the dominant bacteria in the two columns were proteobacteria and bacteroidetes.The microbial community diversity of the biofilm column was increased by addition iron ions,and the biofilm microbial population structure was changed,the abundances of Betaproteobacteriales in proteobacteria and Flavobacteriales in bacteroidetes were increased,so that Fe-AC column had a higher ammonia removal efficiency than AC column at low temperatures. |
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