Study On Removal Of Nickel By Domesticated Escherichia Coli And Decolorization Of Dyes With Three Kinds Of Bacteria

Heavy-metal pollutants and dye wastewater have become the most serious problem through out the world.Metal ions are invisible and can't be degraded, while dyes usually have complex aromatic molecular structure, which make the wastewater of high COD brilliance and intensity colors and low biodegradability. They are difficult to disposal by conventional physical or chemical treatment process mainly becauce of it's expensiveness, energy-costly and secondary pollution. In recent years, numerous metal ions have been treated by non-living biomass very well, except nickel ion. Researchers have found that the metals biosorbed on the surface can be biotransformed after enter into the cell, and dyes will be biodegraded by the enzyme that excreted by living microoganism.Mechanism of Escherichia coli domestication was discussed in this paper. The bacteria was domesticated for three times in the medium by increasing the Ni²⁺ concentration gradullay. Morphological and surface characteristics of E.coli were anlysized by infra-red spectrum, X-ray electron spectra, transmission electron microscopy and light microscopy, meanwhile, plasmid was also anlysized in these processes. Domesticated bacteria that of higher Ni²⁺ accumulation capacity was used to deal with the simulation water, compared to common strain, the accumulation capability turn out to be better. At the same time, three kinds of bacteria were used to decolorize dyes, and to explore the feasibility of microoganism in dye wastewater pretreatment. In this paper we have done the works as follows:1. Selecting the initial concentration of nickel ions for domestication processes When incubated in the Ni²⁺ environment, The emergency response of E.coli was a biochemical process, which was closely related to the concentration of Ni²⁺. Therefore, the effect of concentration of Ni²⁺ on the behaviors of growth and accumulation were studied. The results showed that growth of E.coli was drastically inhibited by the increasing concentration of Ni²⁺. Accmulation capacity was enhanced with the biomass increasd, the maximal Ni²⁺ accumulation capacity occurred in the stationary phase. Results of FT-IR showed that, the Ni²⁺ accumulation mainly depend on the functional groups on the surface of biomass, sunch as–OH, -COOH, maybe protein was also involved in this process. From XPS spectra, we can draw a conclusion that the protein was certainly participated in Ni²⁺ accumulation. TEM observed that the biomorph of cells were changed and the cell wall became frangible after Ni²⁺ accumulation. The maximal accumulation rate of Ni²⁺ was obtained at the concentration of 30 mg l^-1, it is selected as the strain for the later domestication process.2.The primary mechanism of emergency response in domestication processAfter domesticated for three times, E.coli can quickly acclimatize itself to Ni²⁺ medium, and the growth rate was controlled by the Ni²⁺ concentration, the propagated speed of the bacteria increased with the decreasing of the Ni²⁺ concentration gradients. The accumulation capability of domesticated bacteria, which related to the concentration of Ni²⁺ was also advanced. The time for maximal capacity of E.coliâ… was at the stionary phase. There are two kinds of E.coliâ…¡, one was incubated at the concentration of 20 mg·L^-1, while another at 150mg·L^-1, for the former one(E.coliâ…¡C,D), there were two periods of maximal capacity at log phase and stionary phase, repectively, and the latter (E.coliâ…¡E,F) it was at log phase. E.coliâ…¡were domesticated for the third time at the concentration of 300mg·L^-1. For E.coliâ…¢, the periods of maximal capacity were the same to their strains. FT-IR anlysis showed that, besides the peaks of hydroxyl, peaks of amide groups shifted obviously and the peaks of C-O for amylose shifted, as well. All of these biomacromolecules can biosorbe the Ni²⁺ by combining with it. Light microscope and TEM were applied to investigated the microstrueture of cells, and observed that cells were destroyed and fissioned with the Ni²⁺ increased during domestication, furthermore, the cells aggregated together. Plasmid was prepared by NaOH method, and the profiles showed that there was only one plasmid in the E.coli, and it didn't changed in domestication process.3.The removal efficiency of Ni²⁺ with domesticated bacteria Domesticated bacteria that of better Ni²⁺ accumulation capacity was used to deal with the simulation water, the concentration of Ni²⁺ in the sample was in the range of 0 10 mg·L^-1. the tolerance of bacteria to Ni²⁺ became improvement after domestication. At the concentration of 5 mg·L^-1 and10 mg·L^-1, the OD600 for the domesticated E.coli was about three-fold of common one. Removal rate also improved more than 3 times. FT-IR spectra showed that more functional groups had participated in Ni²⁺ accumulation in the sample.4. Study on the decolorization of dyes with three kinds of bacteriaDecolorization behaviors of bacteria on Sunset yellow and Methylene blue were investigated. When the pH was in the range of 2.0-9.0, the absorbance varied slightly. Decolorization experiment showed that the decolorization process of bacteria includes two steps, adsorption and degradation. In the first step, the maximal adsorption rate which depended on the numerous biomass was at the stionary phase, while in the next one, due to the synthesis, excretion and dagragation of enzyme, the maximal decolorization rate was delayed to the death phase. The decolorization rate of three kinds of bacteria for the dyes were different. The E.coli can remove 60% of the colour of Methylene blue, and, decolorization rate of sunset yellow by Staphylococcus aureus was 56%.