Synthesis Of SRB-biochar Composites And Its Application In Removing Heavy Metals From Simulated Acid Mine Wastewater

Acid mine drainage(AMD)is the major pollutant produced during mineral exploitation.AMD has the characteristics of low pH value and high heavy metal concentration,which can easily cause serious environmental pollution and threaten the health of wild animals and plants.At present,most treatment methods are physical or chemical removal of heavy metals.These methods require addition of expensive chemical reagents and supplies,and the generation of secondary pollutants is also another concern.Sulfate reducing bacteria(SRB)are anaerobes existing widely in nature.In the process of growth and metabolism,SRB can reduce SO₄^2-to S^2-,which can complex with heavy metal cations to form insoluble sulfide precipitates.Treatment of AMD using SRB is of great efficient and potential to solve the heavy metal pollution in AMD,and such method can reduce secondary pollution,and lower the expense of the treatment process.However,the strong acidity,heavy metal toxicity of AMD and the anaerobic characteristics of SRB severely limit the application of SRB in the treatment of AMD.Immobilizing SRB on the porous material by the immobilized microorganism technology can reduce the contact of SRB with the dissolved oxygen in the wastewater,and improve the tolerance of the SRB to pH and heavy metals.This technology can effectively improve the survival of SRB in wastewater and improve the overall efficiency of wastewater treatment.In this thesis,a G^-Desulfovibrio strain,called SRB-1 was isolated and purified from the collected lake water samples with a variety of anaerobic culture methods.Another G^-Desulfovibrio type strain,called SRB-2 was purchased from China General Microbiological Culture Collection Center(CGMCC).The growth characteristics of two SRB strains were studied.Four SRB-biochar composites were prepared with two SRBs and two biochars(bamboo biochar,coconut shell biochar).The composites were applied to the treatment of simulated acid wastewater containing Cd²⁺and Zn²⁺.The changes of pH,SO₄^2-concentration and heavy metal ion concentration in the wastewater were measured within 7 days.The treatment effects of composites on wastewater were compared.The results were as follows:(1)Under the anaerobic culture condition of 30?,the OD₆₀₀absorbance of the two SRB strains reached the peak at around the 2-3 days of culture,when the bacterial density was the highest.The optimum growth pH for both SRBs was neutral about 7.When the inoculum size for culturing SRB-1 was 25%,the OD₆₀₀absorbance was the highest and the bacterial density was the highest.When the inoculum size was 10%,SRB-1 had the best reduction effect on SO₄^2-.The optimum inoculum size for culturing SRB-2 was 20%.Under this condition,the OD₆₀₀absorbance was the highest,the bacterial density was high,and SRB-2 had the best reduction effect on SO₄^2-.(2)Bamboo biochar and coconut shell biochar were characterized.The pH of bamboo biochar was 7.33,the specific surface area was 5.83 m²/g,and the total pore volume was 0.0049 cm³/g.The pH of coconut shell biochar was 7.21,the specific surface area was 738.35 m²/g,and the total pore volume was 0.43 cm³/g.Four composites were prepared with SRBs and biochars.They were applied to the treatment of simulated acid wastewater containing Cd²⁺and Zn²⁺.The results showed that SRB-biochar composites could effectively improve the survival ability of SRB in wastewater.Compared with bamboo biochar,coconut shell biochar had larger specific surface area and pore volume,better neutralization effect on wastewater acidity,making SRB grow faster.However,when treating wastewater containing Cd²⁺,the composites of bamboo biochar had a higher reduction rate of SO₄^2-.It could be seen that both biochars have their own advantages.(3)By comparision,it was found that the capability to reduce SO₄^2-to S^2-in SRB-1 was stronger than that in SRB-2 when the composite biochar was the same.The removal rate of Cd²⁺by the composites was similar and reached as high as 90%,and the pH value of wastewater after treatment was between 6.8 and 6.9.The removal rate of Zn²⁺by the composites prepared by SRB-1 and coconut shell biochar was less than 80%,and the pH value of wastewater after treatment was 7.8.The removal rate of Zn²⁺by the other three composites all reached 99%,and the pH value of wastewater after treatment was between 7.2 and 7.4.The results of the pseudo-first-order kinetic equation model showed that the composites of strain SRB-2 had a stronger ability to remove Zn²⁺than those of strain SRB-1.In general,the type strain SRB-2 has a better removal effect on Zn²⁺,and the stability of SRB-1 composites to remove heavy metals needs to be strengthened.The composites prepared in this study have generally good effect on the treatment of simulated wastewater,and further research is needed to improve the removal efficiency of heavy metals by SRB.