Study On Biosorption Of Heavy Metal Zinc Ions In The Sewage By Microorganisms

The pollution of heavy metal in the environment is a serious problem, which canaccumulate in the food chain to increase the toxic effect. The conventional treatmentmethods, such as chemical precipitation, electrolysis, ion exchange, possessed someshortcomings, including operation complexity, high cost, and generating secondary pollution,and so on. In recent years, the biological adsorption method has attracted great attentiondue to its high efficiency and environmental friendly.In this study, four strains of bacteria were identified by screening polluted water forresistance to zinc ion. One of the strains （wlsh-4） possessing the highest zinc-resistance waschosen to continue the studying of zinc adsorption experiment.16S-rDNA sequenceanalysis indicated that wlsh-4belonged to proteus bacterial group, and phylogenetic treeshowed that the closest standard strain to wlsh-4was proteus penneri strain NCTC12737.The strain wlsh-4was found to be able to absorb Zn²⁺in the water. Further studyshowed that the majority of the absorption originated from the bacterial cell bodies bycomparing the adsorption rates for the medium, the culture supernatant, the fermentationsolution, and bacterial cells; the fermentation supernatant also displayed some adsorptioneffect.The growth condition had great influence on the Zn²⁺adsorption function of wlsh-4;the optimal condition was temperature30°C, pH7, the shaking speed190rpm, and the timeof culture13h. At the optimal condition, the adsorption rate of Zn²⁺was up to66.67%.In addition, the effect of other factors on the adsorption efficiency was studied,including Zn²⁺initial concentration, adsorption time, temperature, amount of bacteria, andthe pretreatment to the bacteria with the acid and the alkali. Through the orthogonalexperiments, the optimal Zn²⁺initial concentration was200mg/L, incubation temperaturewas40℃, incubation time was6h; at these conditions, the adsorption rate of Zn²⁺wasimproved up to75.38%. When the bacteria were treated with various concentrations ofacid and alkali, the adsorption rates were not affected. Thus we chose the fermentationsolution without any pretreatment to adsorb the Zn²⁺existing in the actual sewage.According to the adsorption conditions that had been determined, wlsh-4was tested for the adsorption of Zn²⁺in the leakage water of Tailing Lake of Baotou Steel Company.We found that the Zn²⁺adsorption rate of the free bacteria was44.73%. When thebacteria were immobilized on plastic string netted bags, the adsorption rate forZn²⁺could reach up to65.4%; so, this technology showed a promise in the practicalapplication.