Research On The Growth Characters Of Sulfate-reducing Bacteria And Removal Of Heavy Metals

Removal of heavy metals by sulfate-reducing bacteria(SRB)is a new and potential technology. In this paper, mixed SRB were domesticated from anaerobic sludge in an Internal Circulation anaerobic reactor of a paper mill by sulfate, some factors which affect SRB reducing capacity were observed. Based on that, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were the target object, their toxic effects on SRB were examined, and so did their removal effect by SRB, the mechanism for removal of heavy metals by SRB was finally preliminary investigated. This paper concludes as follows:(1)The optimum conditions of SO₄^2- reduction by SRB were as follows: initial pH value 7.0, the ratio of COD/ SO₄^2- 3, amount of Fe²⁺ 200 mg/L. When the initial pH value were at the range of 4-9, the SRB system has good buffer capacity, the pH maintained at 7.05-7.5, while the initial pH value was 3, the buffer capacity of this system was inferior.(2)SO₄^2- reduction by SRB was observably inhibited by NO₃^-, and the inhibitory effect was strengthend with the increasing of NO₃^- concentration. In the reaction process, the pH value of systems containing NO₃^- was all higher than that of absence of NO₃^-.(3)Generally speaking, SO₄^2- reduction by SRB was inhibited by Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺, and the inhibitory effect was strengthend with the increasing of heavy metals concentration, the order was Cd²⁺>Cu²⁺>Zn²⁺>Pb²⁺. Pb²⁺ can promot SO₄^2- reduction by SRB when its initial concentration was less than 25 mg/L.(4)In the process of SO₄^2- reduction, under different concentration of heavy metals, the pH values increased slightly at the beginning, and then went steady. In the systems containing Cu²⁺ and Pb²⁺, whose concentration were low, the pH values were higher than that of control group at equilibrium point, when the concentration was higher, the pH values decreased. In the systems containing Zn²⁺ and Cd²⁺, the pH values were all lower than that of control group, and when the concentration was higher, the pH value was lower.(5)The inhibitory order of Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ to TTC-DHA was Cd²⁺>Cu²⁺>Zn²⁺>Pb²⁺. The concentration of Cu²⁺,Zn²⁺ and Cd²⁺ was higher, the TTC-DHA was lower, there was a resistance peak of TTC-DHA when the Pb²⁺ was 25 mg/L.(6)Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ could be effectively removed by SRB, and the effet of removal of Cu²⁺, Zn²⁺ and Pb²⁺ was higher than that of Cd²⁺. Different initial concentration of one heavy metal had different removal rates. (7) Cu²⁺, Zn²⁺ and Pb²⁺ were removed in the form of sulfides, SO₄^2- reduction forming H₂S by SRB played a leading role in these processes; while Cd²⁺ was removed in the form of Cd(OH)₂, which was in that Cd²⁺ reacted with OH- generating precipitation of hydroxide when the pH value increased.