| As the economy has developed rapidly and the industrialized progress has been accelerated, environmental pollution becomes more and more serious. Coking wastewater is one of the major environmental problems is confronted with, whose treatment become an attention focus. Components in coking wastewater are complex, in which contain high concentration of ammonia-nitrogen and a number of toxic and difficult decompounded organic compounds. Great changes usually happened to the quality of wastewater and the flow of wastewater. It is one of tough problems in the treatment of industrial wastewater. At present, activated sludge is the most popular treatment system on coke plant wastewater, which is economical and convenient method. It can remove phenol and COD efficiently from coking wastewater. However, ammonium in wastewater can not be removed by this method, which can not reach the national discharge standards. Thus, how to remove ammonium-nitrogen from coke plant wastewater efficiently and economically has becoming a hot research field these years. In recent years, some heterotrophic nitrifying strains have been isolated from environment. Compared with traditional autotrophic nitrifying strains, heterotrophic nitrifiers have the characteristics of larger growth rate, higher production of cells higher adaptability to environment, higher efficiency of removal NH4+-N. Recently, heterotrophic nitrifiers have been intensively studied as potential microorganisms that may be used to overcome problems inherent in the conventional method. However, most of study has focused on low concentration ammonium discharged from domestic wastewater, with less attention on the treatment of high concentration ammonium in coking wastewater.In a high concentration substrate medium, four heterotrophic bacteria with high removal efficiency of ammonium, named W1,W2,W3,W4respectively, were isolated from activated sludge of coking wastewater treatment facility. In this paper, the characteristics of strain W1have been studied in detail. The bacterium was Gram-negative, rod-shaped, and identified preliminarily as Alkaligenes sp. according to its morphological and physiological properties and its16S rRNA gene sequence analysis. In the high concentration ammonium medium (400mg/L NH4+-N), the effects of C source, N source, C/N ratio and initial pH of medium on ammonium removal were investigated in order to determine the optimal condition for strain W1. The maximum ammonium removal was around95%in4days in an improved medium. In order to identify whether the stainW1has the ability of aerobic dentrification, the production of N2gas was examined in a closed system that was full of pure oxygen at the beginning. N2gas was detected in the system after4days of cultivation, which further testified that strain W1has heterotrophic nitrification and aerobic denitrification abilities simultaneously.In order to reduce the toxicity of environment to bacterium while maintaining its microbial activity, strain W1has been immobilized with polyvinyl alcohol and sodium alginate. Compared with the suspension of bacterium, the ammonium removal ability of W1was highly increased with immobilized microorganism techniques. The average removal rate of ammonium was enhanced from99.05mg/L/d to140.45mg/L/d. Immobilized granular of strain W1presented excellent ammonium removal ability. Meanwhile, in order to be used in treatment of coking wastewater excellently, Immobilized granular has been domesticated in this study. After4days of cultivation, the maximum ammonium removal was up to94.50%in coking wastewater, which indicated the good nitrifying ability of granular. Immobilized granular of strain W1is suitable for use in industrial wastewater treatment. |
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