Screening Of Heavy Metal-Tolerant Strains And Their Application To The Remediation Of Contaminated Soil

The traditional remediation methods of the soil contaminated by heavy metals were mainly physical, chemical and biological methods. Bioremediation has become the main treatment technology of contaminated soil for which has the advantages of low cost and could not cause secondary pollution compared to the physical and chemical remediation. Plant and microbe combined remediation had been paid much attention in recent years, and has made significant progress. The interaction of rhizosphere-microbial systems could effectively improve the ability of contaminated soil bioremediation. How to separate the microbial strains which can tolerate high concentrations of heavy metals and to enhance phytoremediation had been the focus on the bioremediation, but the plant and microbe comcined remediation were studied less. We selected the microbial strains to study its ability to promot the plant accumulating Cd and Pb, and to apply to the remediation of the soil contaminated by heavy metals.The microbial strains which can tolerate high concentrations of lead, cadmium were separated from the soil contaminated by heavy metals, and their biological properties were identified. The results indicated that Hypocrea virens selected can tolerate high concentrations of lead and Paecilomyces lilacinus selected can tolerate high concentrations of cadmium. The two strains had good adaptability in the environment, which could grow well at 15～30℃and at pH 4-12, the best growth and sporulation temperature was 25～30℃, the best mycelial growth was at pH 5-9. The tolerance of micro-organisms for Pb2+and Cd2+was the premise of pollution control of the heavy metals, so that the fungi provide good material for the microbe and plant combined remediation.The myceliums were used for the biosorbents of the adsorption experiments, and the efficient impacts of the living cells of Hypocrea viren and Paecilomyces lilacinus were observed at different temperatures, the amount of bacteria, pH values, concentrations and their adsorption kinetics and isotherms. The results indicated that the adsorption capacity increased whereas the removal rate decreased with the quality of the mycelium and the initial concentration of lead increasing. The pH value was one of the important influence factors, the optimum adsorption of pH was 5 and the adsorption capacity of Pb2+of the living cells was 53.56 mg/g D.W. (dry weight). the removal rate was 20.65%; the optimum adsorption of pH was 7 and the adsorption capacity of Cd2+ of the living cells was 28.5 mg/g D.W. (dry weight), the removal rate was 12.0%. The ideal reaction temperature was 30℃, the adsorption capacity was 53.7and 45.4 mg/g for Pb2+ and Cd2-Elovich equation, double-constant equation could describe the characteristics of the isotherm kinetics of mycelium adsorbed lead, and double-constant equation could describe the characteristics of the isotherm kinetics of mycelium adsorbed cadmium. The adsorption rate of Hypocrea virens to lead ion are faster than the Paecilomyces lilacinus to cadmium ions. Langmuir and Frendlich equation can simulate the process of adsorption isotherm while the Langmuir model was more suitable for lead and the Frendlich model was more suitable for cadmium. The stability and affinity of Hypocrea virens to lead ion are better than Paecilomyces lilacinus to cadmium ions. The meoretical maximum adsorption capacity of the living cells of lead and cadmium reached 126.58 and 90.9 mg/g D.W. (dry weight), which showed that they had potential capacity for development and application in future.Solaum nigrum was cultivated in the greenhouse and the strains were inoculated in soil, and the remediation effect of plant and micro-organisms was examined. The results showed that the fungus promoted growth of the hyperaccumulator, and enhanced the accumulation ability of the plant. Paecilomyces lilacinus had a better effect to promote the plant accumulating Cd by 35.5% at high concentration in soil. Hypocrea virens could not improve significantly the effect of accumulating Pb under single Pb pollution. The liquid mixture of Paecilomyces lilacinus and Hypocrea virens promoted the plant accumulating Cd and Pb by 20.6% and 64.8% at high concentration treatment. The highest accumulation coefficient of Cd was 4.25. while that of Pb was lower relatively.