Study On Treatment Of Metal Chromium Using Supported Nano-valent Iron And Bacillus Mycoides Composite System

In recent years, with the rapid development of industry, the post-processing of plating, metallurgy, leather manufacturing, dyeing industries, etc during the development is yet not perfect. These industrial effluents which enter the water could endanger the growth of aquatic animals and plants and endanger human health through the food chain. Therefore, the prevention and treatment of heavy metal pollution caused people's attention. The traditional physical or chemical treatments are costly and easy to cause secondary pollution, etc. There is an extensive application prospect for bioremediation in prevention and control of heavy metal pollution.Based on previous reaserch, a strain with dechromisation was further investigated. It was identified as Bacillus mycoides named Bacillus mycoides 200AsBl,200AsB1 for short. In addition, physicochemical factors on the growth and the dechromisation of the strain have been studied. Sapindus activated carbon supported nano zero-valent iron ?AC-nZVI? was prepared in our study and then were blended with strain 200AsB1 to prepare the immobilized AC-nZVI microorganisms beads. Meanwhile, the chromium removal ability of immobilized beads in artifical wastewater was stuied which can provide fundamental basis for parctical application.The results are as follows:1. The strain 200AsBl which has been isolated in our previous works was identified as Bacillus mycoides through 16S rRNA and phylogenetic trees analysis. The accession number is KU499950.1.By analyzing the growth and chromium removal ability of the strain 200AsB1 in LB medium spiked with 0-125 mg/L Cr⁶⁺ a conlusion was drawn that the LC50 was63.92 mg/L. Bacillus mycoides 200AsB1 can grow well in relatively hign concentration of chromium condition. Cr⁶⁺ was removed completed at the concentration of 50 mg/L which indicate that it has hign tolerance and removal ability for Cr⁶⁺. By obserbation of the physicochemical factor on the growth and the dechromisation of strain 200AsB1 including temperature, pH as well as inoculation it was clear that the effect of removing hexavalent chromium of the strain is the best at 30?, pH 8. The temperature is favorable to the effect of removing hexavalent chromium, but it will has certain effect on it with the increase of the temperature. Inoculation was found to have no significant effect on the effect of removing hexavalent chromium.2. It was found that the surface apparent became irregular which was slightly harsh and emerged with folds and is very different with the cells before through scanning electron microscope ?SEM? studies on the morphology change. Determination the concentration of total chromium and hexavalent chromium after The strain 200 AsB1 grown in LB medium spiked with Cr⁶⁺showed that both concentration of total chromium and hexavalent chromium were decreased over the time which means the main way of removing chromium is through disoxidation. Simultaneously, the determination of hexavalent chromium of the samples which were divided into two groups, the centrifugal and uncentrifugaled Samples indicated that the chromium removal ratio of the centrifugal sample is 15% higher that the other. It was clear that a small percentage of the chromium removal function of the strain 200AsB1 is through surface adsorption. It was found that there is a shift in the 817-919cm^-1 ?hexalvant chromium?band which means the existence of surface adsorption by analyzing the changes of surface function groups through Fourier transform infrared spectrum ?FIRT?. In conclusion the main process of chromium removal is not through disoxidation, and there exist surface adsorption,besides there may be even exist internal adsorption.3. Sapindus activated carbon ?AC? was used as supported materals to prepared AC-nZVI by liquid phase reducing method. The holes of varying sizes at the AC-nZVI surface were observated by SEM which can provided a stable environment for microorganisms. It was found that AC, nZVI and AC-nZVI were effective on the Cr⁶⁺ removal after comparison. The Cr⁶⁺ removal efficiency of three materials with 0.1 g dosage in 50 mg/L chromium aqueous solution from low to high were AC, nZVI and AC-nZVI. The removal efficiency of AC-nZVI can reach 100% in 25 minutes. Therefore, supported nZVI was used as late-stage study material.4. The optimum condition for the preparation of AC-nZVI and microorganisms immobilized beads is as follows?50 mL system?:the ratio of sodium alginate ?SA? was 2%, the AC-nZVI addictive content was 0.25 g, the initial bacteria amount for embedded was 300 mL (OD_600nm= 1.0) and the immobilized time was 0.5 h. The immobilized beads which were prepared under this contidion had good flexibility and mechanical properties. It also has excellent mass transfer with the diameter of 6 mm. The removal efficiency of the immobilized beads in LB medium spiked with 50 mg/L Cr⁶⁺reached 94%. The removal efficiency of the immobilized beads in 50 mg/L Cr⁶⁺artifical electroplating wastewater with various heavy metals reached more than 44%. It showed that AC-nZVI and microorganisms immobilized beads has a prospect for application in chromate wastewater.