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Isolation, Identification, Degradation Characteristics and Immobilization of Sulfide-Oxidizing Bacteria

Author: WangHuiXiang
Tutor: ChenJianMeng
School: Zhejiang University of Technology
Course: Environmental Engineering
Keywords: Biodesulfurization Sulfide High-efficiency bacteria Metabolic characteristic Immobilization
CLC: X172
Type: Master's thesis
Year: 2011
Downloads: 13
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Abstract


More and more energy has been expanded with economic developing, and the research of biodesulfurization technique will become the main issue for environmental protection along with the strength of environmental protection regulation. In this thesis, the degradation characteristics of the dominant bacteria isolated from activated sludge were studied systematically, and the immobilized bacteria was constructed to improve the desulufrization activity.Four Sulfide-oxidizing bacteria were acclimated and isolated from wastewater collected from the wastewater treatment plant of Zhejiang Ocean Pharmaceutical. Based on their morphological, physiological biochemical characteristics,16S rRNA sequence analysis, and the Biolog identification system, these strains were identified as Rhizobium sp, Ochrobactrum sp, Sphingobacterium sp, Agrobacterium sp, which were designated as T3, B3, T4and B4respectively. Besides B3, the other three strains were proposed as new species which can degrade sulfide efficiently according to the relevant literatures.The degradation abilities of sodium sulfide by these four isolates were investigated. It was found that the removal efficiency in strain T3was more efficient than that in the other three strains. The optimal pH and temperature for T3growth and degradation were8.0and30℃, respectively. A variety of carbon sources could enhance the removal efficiency of T3, while the best nitrogen source was ammonium chloride. In the optimum conditions, when sulfide concentrations was lower than300mg/L, the strain grew well and sulfide could be efficiently degraded by T3within2days. When sulfide concentration ranged from400mg/L to500mg/L, the strain grew slowly and the degradation efficiency was also decreased. When sulfide concentration was up to500mg/L, the degradation efficiency was significantly decreased. The results showed that toxic substances may be released when the degradation was conducted in such high concentration, in which the strain growth and degradation were inhibited. During the course of sodium sulfide oxidation by T3, various intermediate metabolites were analyzed, and it indicated that the pathway of sulfide degraded by T3is followed by S2-→S2O32-/S0→SO32-→SO42-The further study on the degradation characteristic and degradation kinetic of hydrogen sulfide by T3were examined. The results showed that degradation efficiency of hydrogen sulfide in T3was the same as that of sodium sulfide. Furthermore, the growth rate of T3and H2S degradation rate were accordanced with Haldane kinetic equation, and the kinetic parameters of μmax was0.1652g/(g·h), Ks was24.23mg·H2S/L and Ki was665.35mg/L.After analysised by antagonizing experiments and different combinations of four strains, it was found that the mixture of T3and B3was the one for H2S degradation. Then the mixture bacteria were immobilized by sodium alginate and sodium alginate-PVA. Compared with free cells, it was founded that in the same concentration level, the H2S degradation abilities of three kinds of cells was followed by sodium alginate-PVA immobilized cells>sodium alginate immobilized cells> free cells. Furthermore, sodium alginate-PVA immobilized cells also had good mechanical strength and matrix permeability.Hence, the superior mixed bacteria were immobilized by sodium alginate-PVA complex carrier. After examined the activity of immobilized cells, expressed by the H2S degradation ability, it was found that the optimal operating conditions of immobilization cells were fixed on:2%sodium alginate and7%PVA,24h for cross-linking time in4%boric acid and1%calcium chloride solution,2~-3mm for particle size of immobilized cells,0.3g/L of package bacteria,4g of immobilized cells ammount. And, more wide rang with pH, temperature and H2S concentrations could adapt to in immobilized cell than that in free cells. The immobilized cells have a high H2S degradation capacity in pH5~10, temperature25~40℃, H2S concentration100~400ppm. When the H2S concentration were higher than400ppm, degradation capacity of free cell decreased quickly, while that of immobilized cells could maintain more than60%of degradation percentage, and the repetition of desulfurization capacity was greatly improved by immobilized cells, which would provide the possibility for industrial applications.

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