Study On Degradation For Ammonia Nitrogen In Water Using Immobilized Microorganisms On Magnetic Composites

With the rapid development of industry economy,the problem of water environment pollution is becoming more and more prominent and it has caused widespread attention of the whole society.Ammonia nitrogen is a toxic inorganic pollutant of hardly degradable in water,the industrial ammonia nitrogen wastewater is difficult to handle due to its complex composition and large emissions.Biological treatment technology has been widely applied to sewage treatment because of its high removal efficiency,no secondary pollution and low cost.In recent years,immobilized microorganisms denitrification technology has become an important research field of wastewater treatment.In this paper,different spherical immobilized microbial catalysts were prepared by the embedding method and the coating method.Immobilized microorganisms was prepared by inexpensive,non-toxic,biocompatible carrier materials such as chitosan,sodium alginate,cellulose and other materials.The immobilized microorganisms were prepared by compounding and modifying for different materials,and the catalytic performance of immobilized microorganisms in the treatment of simulated ammonia nitrogen water and coking water from coal chemical production bases was studied.The mainly research content and conclusions were summarized in the following three parts:In the first part,preparation of chitosan-cellulose-dopamine immobilized microorganisms and chitosan-polyvinyl alcohol immobilized microorganisms by chitosan embedding method.Immobilized microorganisms(chitosan-sodium alginate-Fe3O4)was prepared by chitosan coating method.Immobilized microorganisms was prepared by dopamine cross-linking polymerization ionic liquid co-solvent method and dopamine-modified cellulose was prepared immobilized microorganisms.Under the same conditions,the immobilized microorganisms prepared by dopamine modified cellulose have more advantages in degrading ammonia nitrogen process,the degradation rate of ammonia nitrogen was 72.46%.The immobilized microorganisms(chitosan-3-aminopropyltriethoxysilane modification polyvinyl alcohol)were used to degrade 50mg/L simulated ammonia-nitrogen water.After reacted for 120h,the degradation rate of ammonia nitrogen was 82.3%.Ammonia nitrogen(50mg/L)simulated water was treated with free microorganisms and immobilized microorganisms(chitosan-sodium alginate-Fe3O4).When reacted 132h,its degradation were 63.10%and 99.50%respectively.In summary,it was found that the degradation efficiency of ammonia nitrogen by chitosan-sodium alginate-Fe3O4 immobilized microorganisms prepared for chitosan coating method was better than that by chitosan-cellulose-dopamine and chitosan-polyvinyl alcohol immobilized microorganisms prepared for chitosan embedding method.Meanwhile,the effects of Fe3O4 content and mass concentration of chitosan on ammonia nitrogen degradation were investigated.The optimum conditions were the content of Fe3O4 13%and the mass concentration of chitosan 0.2%.In the second part,the simulated ammonia nitrogen water was treated by immobilized microorganisms(chitosan-sodium alginate-Fe3O4).The single factor study showed that the suitable temperature of the immobilized microorganisms was 10?40? and the suitable pH value was 7?9.After acclimated by ammonia nitrogen,the velocity of ammonia nitrogen degradation has increased dramatically.The ammonia nitrogen(100mg/L)was treated for 72h and the degradation rate reached 96.30%.The intermediate analysis showed that the accumulation of nitrite nitrogen in the initial concentration of 50mg/L and 100mg/L of ammonia nitrogen was 0.0279mg/L and 0.0234mg/L,respectively,and the accumulation of nitrate nitrogen was 1.83mg/L and 1.48mg/L,indicating that the reaction occurred simultaneous nitrification and denitrification.And after biodegradation for 8 times,the immobilized microorganisms catalyst remained reactivity,resulting in the degradation rate of ammonia nitrogen being 94.71%.The effects of temperature,pH value and adding amount of immobilized microorganisms(chitosan-sodium alginate-Fe3O4)on the degradation of ammonia nitrogen were investigated using the response surface optimization method.The optimum parameters were as follows:temperature 30?,pH 7,the amount of immobilized microorganisms 300g/L.Under ammonia nitrogen conditions,the effect of phenol on degradation of ammonia nitrogen by immobilized microorganisms(chitosan-sodium alginate-Fe3O4)and the degradation of phenol were investigated.The results showed that phenol had a certain inhibitory effect on the degradation of ammonia nitrogen.While the concentration of phenol is increasing,its microbial activity will be lower and ammonia degradation rate will be decrease.After reacted for 144h,the concentrations of 50mg/L,100mg/L,150mg/L,and 200mg/L of phenol all reached the national emission standards.In the third part,coking water(ammonia nitrogen concentration of 41.21mg/L)from the coal chemical production base was treated with the immobilized microorganisms(chitosan-sodium alginate-Fe3O4).After reacted for 72h,the degradation rate of ammonia nitrogen reached 94.22%.While the same experiment with the free microorganisms,the degradation rate of ammonia nitrogen was only 41.93%.The analysis of intermediate product showed that the accumulation of nitrite nitrogen during the degradation of ammonia nitrogen by free and immobilized microorganisms were 0.3 mg/L and 0.027 mg/L,the accumulation of nitrate nitrogen were 3.59 mg/L and 0.575 mg/L,respectively.It embodies that the magnetic immobilized microorganisms can treat coking water better than free microorganisms.After the immobilized microorganisms was used 5 times,the degradation rate of ammonia nitrogen was still higher than 95%,which indicated that it can effectively degrade ammonia nitrogen in coking water and provides an experimental basis for magnetic immobilized microorganisms to degrade coking water produced in the coal chemical industry.