| Acid mine drainage (AMD) formed when sulfide minerals in coal seam and surrounding rock were exposed to oxidizing conditions by chemical oxidant and oxidation of ferrous sulfur bacillus in high sulfur coal and metal mining. AMD usually had a low pH vlue, in addition to rich in Fe3+and SO42-, and leached heavy-metals in the associated minerals, such as lead, copper, cadmium, zinc, chromium, etc. It caused serious harm for mining production, groundwater resources and ecological environment. In this study, permeable reaction bed of immobilized sulfate reducing bacteria with Fe-C reduction was employed for in situ removal of the heavy-metals in acid mine drainage. It had important significance for safety production of high sulphur coal mine and protection of groundwater resources and the ecological environment in mining area.First, for the study of the effect of porous reaction bed fixed sulfate-reducing bacteria in situ remediation of heavy-metal in acid mine water, in the anaerobic reactor, the suitable medium of sulfate reducing bacteria and their tolerance to heavy metals was studied.Moreover, the treatment of laboratory simulation heavy metal wastewater by the domestication of sulfate reducing bacteria was investigated.The results show that the domestication of sulfate reducing bacteria mixed flora may be effective for removalling wastewater containing Cu2+, Pb2+, Zn2+, Cd2+.The removal rate of Cu2+, Pb2+, Zn2+can reach above90.4%, and the removal rate of Cd2+also can reach above75.67%.Second, in order to explore the best process conditions, the treatment conditions of the heavy-metal by sulfate reducing bacteria was researched by response surface methodology at the index of Pb2+、Cd2+、 Cu2+、Zn2+and Fe2+average removal rate. The effect of variables and their interactions was research using the Box-Behnken (BB) design. With quadratic polynomial regression equation prediction model as the foundation, The results showed the best process conditions for the initial pH value of7.1; the culture temperature of34.8℃for5days, and the higher removal rate the lower initial concentration, under which condition, the removal rates of heavy-metal were up to98.81%、93.1%、96.62%、92.73%、93.41%.At the same time, the Box-Behnken design matrix and response surface methodology (RSM) had been applied to design the experiments to evaluate the interactive effects of four most important operating variables: pH (2.0-4.0), temperature (30-40°C), iron/carbon ratio (1/2-3/2) and iron carbon amount(2-4) on removal of Pb (Ⅱ), Cu(Ⅱ), Zn (Ⅱ) and Cd (Ⅱ) ions in acid mine drainage with mico-electrolysis (ME). The total29experiments were conducted in the present study towards the construction of a quadratic model. Values of "Prob> F" less than0.0001indicate that model terms were significant for the removement of Cr (Ⅵ), Ni (Ⅱ) and Zn (Ⅱ) ions. Maximum removal of Pb(Ⅱ), Cu(Ⅱ), Zn(Ⅱ) and Cd(Ⅱ) were observed82.23%,89.48%,69.30%,75.07%at pH3.08, temperature38.75°C, iron/carbon ratio6:5and iron carbon amount39.7g/L.And then, in order to explore the best process conditions, pH, temperature, time and Fe-C/SRB ratio, the treatment conditions of the heavy-metal by SRB/Fe-C was researched by the Box-Behnken (BB) design. The results showed that the response surface method can effectively optimize the conditions of the SRB/Fe-C system to remove heavy-metals. Variance analysis showed that R2=0.9993, very closed to1, indicated that the experimental results and the quadratic regression equation prediction model were significant. Maximum removal of Cu2+, Pb2+, Zn2+and Cd2+were observed99.53%,99.58%,98.30%and99.53%at pH7, temperature30°C, Fe-C/SRB ratio3:10and7days. Compared with a single system, the removal efficiency improved significantly. Finally, the treatment of the heavy-metals in acid mine drainage by using laboratory simulation permeable reaction bed(PRB) was studyed. Results show that the system is stable operation2months, and the removal rate of heavy metal ions was nearly100%. The Zn2+and Cd2+removal rate began to fall after14days, and the removal of Cu2+and Zn2+began to slow down after36days. At the same time, the Fe-C system had increased the pH value of simulated AMD, from pH3rapidly increased to the pH7, and the effluent reached7or8. |
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