| With rapid development of industrial technologies such as electroplating, tanning, dyeing and others, chromium(Cr) is widely used in industrial production. Untreated waste generated from these process containing Cr(VI) discharged directly into the environment would cause serious pollution on the environment. Meanwhile, Cr(VI) has highly toxic on biological systems, has mutagenic, carcinogenic and teratogenic effects on organisms, which belongs to the first class of pollutants. And Cr(VI) water-soluble, easy to move, so it is easy to transfer, away off initial contamination of the site. The Cr(III) is relatively inert and strong, not easy to move, has low bioavailability; In addition, the toxicity of Cr(VI) compound is approximately 100 times than Cr(III), mutagenic rate is about 1000 times than Cr(III).Conventional electroless and electrochemical treatment process is generally reduce the Cr(VI) to Cr(III) in the aqueous solution, it precipitate reduce p H of the solution adjust to near neutral conditions to reduce Cr(VI) concentration. However, these methods are considered undesirable, because the processes require large number of expensive chemicals, and their removal efficiency can not meet the actual demand, meanwhile in the repairing process would produce a lot of chemical recycling sludge which is not easy to collect. Bioremediation methods to restore Cr(VI), namely use microorganisms reduce chromium Cr(VI) to more stable, less toxic Cr(III) and then adsorp,which considered to be an effective solution to Cr(VI) contaminating environment; the potential role of microorganisms used as biological redactor on Cr(VI) has been demonstrated in a variety of experiments can be restored. In addition, the required equipment bioremediation method is simple, small investment, little harmful to the environment, it should be promoted in the Cr(VI) to remove terms.Therefore, converting the virulent, highly water soluble Cr(VI) to less toxic, poorly water-soluble Cr(III) and then adsorbed by microorganisms is considered to be an effective method recovering chromate contaminated soil and water systems.The experiment has isolated 20 strains from soil at Shanghai abandoned steel factory, through tolerance and adsorption experiments selected a strain M-13 which has strong ability to repair Cr(VI), the molecular biological identification and morphological identification showed this strain is Trichoderma citrinoviride M-13.We isolated a strain of Trichoderma citrinoviride M-13 from the soil in a Shanghai abandoned steel mill, which has strong ability to repair Cr(VI), and the influencing factors of repairing were studied. Using Modified Martin-type agar culture medium to culture the strain Trichoderma citrinoviride M-13 and collecting mycelium, then a certain amount of mycelium put into an aqueous solution containing Cr(VI), the filtrate and mycelium of chromium were determined. We have studied the growth curve of M-13 and different training time for repairing rate of Cr(VI), and studied the repairing influence of p H, temperature, time, initial concentration of Cr(VI) and the initial bacteria amount for repairing rate of Cr(VI), and also using ICP-MS to verify the amount of Cr(III) and determine its concentration. Trichoderma citrinoviride and collecting mycelium M-13’s repairing rate on total chromium and Cr(VI) were 37.2% and 78.4% respectively. The ability of repairing mycelium of this srtain was 0.54mg/g, the content of mycelium reaches the maximum at 72 h, and mycelia’s repair rate for Cr(VI) is highest when culturing at 42 h and 72 h. When p H 1.09, the temperature at 30 °C, the amount of hyphae in 0.5 g, initial concentration of Cr(VI) in 100mg/L, using ICP-MS to determine Trichoderma citrinoviride and collecting mycelium M-13’s repair rate for Cr(VI), and the results are as follows: the concentration measured values of Cr(VI) is under test, and Cr(III) was 61.1 mg/L, which showed that Trichoderma citrinoviride and collecting mycelium M-13 can be completely removed Cr(VI), 61.1% of Cr(VI) can be reduced to Cr(III) and only 38.9% of Cr(VI) is adsorbed, so the strain of M-13 can repair Cr(VI) in sewage very well.Mutagenesis the strain using ultraviolet light, with the separated and identified strain Trichoderma citrinoviride as a starting strain preserved in the experiment. Through ultraviolet mutation, Screened out a resistant Cr(VI) strongly, high reduction efficiency, and has a certain genetic stability of strain M-13M(mutagenesis). The resistant to Cr(VI) and repair ability on Cr(VI) of the mutant strain conducted in experiments. The result showed that, when the conditions for mutagenesis: UV intensity ws 30 W, an irradiation distance of vertical wa 30 cm, the irradiation time was 120 s, Trichoderma citrinoviride M-13 of the mortality rate was 92.3%, selected strain M-13M4 in this condition, with good genetic stability. With this strain, on the repair conditions: initial mycelium inputs of 0.17 g, the initial Cr(VI) at a concentration of 120 mg/L, initial p H value of 1.21, Cr(VI) in the repair rate of up to 94.2%. The results showed that the strain of Trichoderma citrinoviride M-13 after the UV mutagenesis, and its resistance to Cr(VI) capabilities and Cr(VI) to repair capability has been improved to some extent.Studied the biological characteristics of M-13 about Cr(VI) and Cr(III), it shows in Cr(III) adsorption process, the degree of fit of Langmuir equation is higher than Freudlich equation, so the adsorption process of Cr(III) is more in line with Langmuir isotherm equation. The process is a uniform surface adsorption process. In Cr(VI) adsorption process, the degree of fit of Freudlich equation is higher than Langmuir equation, which is different from the adsorption process of Cr(III). This may because the adsorption process of Cr(VI) is not only a surface adsorption processes also include a more complex redox reaction. So the degree fited with the Langmuir monolayer adsorption model equations is not very high. |
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