Microbial Treatment Of Heavy Metals In Sewage

The heavy metals were disposed into the environment as industrialized rapidly. Unlike many organic wastes, heavy metals can not be bio-degraded. It's accumulated in the food chain as to increase the toxicity hazard. The heavy metal waste water became a serious problem because it is difficult to decontaminate. It is paid attention to treat heavy metals with microorganisms along with the developing of the environmental technology. In this study, it was clarified to adsorb Pb²⁺ and Zn²⁺ with microorganisms, and the removal of heavy metals with biological reduction of sulfate.Several strains of cold-adapted bacteria with zinc-resistance were screened mean whiles the adsorption capacity to zinc of these strains were analyzied. The growth conditions of strain 39 with high resistance to zinc and strain 21 with good adsorption capacity to zinc were analyzied. As results, the optimum growth temperature of strain 39 and strain 21 were also 8-21°C, the optimum growth pH of these two strains were 6-8 and 6-8.5, respectively. At the optimum conditions, it took these two strains 36h to reach the stationary phase.Two fungal strains C —1 and 3—2 with high adsorption capacity and resistance to zinc and lead were screened. The strain C—1 was characteristic of great biomass, rapid growth and was able to produce spores even in the concentration of 100mg/L zinc ions. The optimum growth conditions of these two strains were temperature 25°C, pH 5.5. The strain C-1 was identified as Trichoderma viride.The adsorption influence factors of strain C-1, such as concentration of zinc, temperature and the mass of mycelial pellets. As results, the adsorption capacity increased with the concentration of zinc ions, it could adsorb zinc ions at the temperature between 4-37°C, however, the optimum adsorption temperature was 25°C. The adsorption capacity decreased with increasing of the mass of mycelial pellets, however, the removal efficiency of zinc could be improved.Sulfate reducing bacteria(SRB)are strict anaerobes, which dissimilate organics using sulfate or other oxidation state sulfide as electron acceptors. The formation conditions and affecting factors of SRB metabolic mechanism, such as carbon source and nitrogen source, was studied. The methods that neutralization precipitation and sulphide precipitation, were discussed and their advantage and disadvantages were compared in several aspects. Theexperimental results showed that S^2- produced from biological reduction of sulfate with SRB can chemically precipitate heavy metals and remove the insoluble metal sulfide. The principle, characteristics and influential factors of heavy metals removal with biological reduction of sulfate are studied in this paper. It is feasible and effective to removal heavy metals with biological method and it has reliable significance for the treatment of heavy metals wastewater.