The Aerobic/Anaerobic Reduction Of Cr(?) By Bacillus Sp. Cr02 And Its Effect Factors

The large amount of chromium slag in China leads to the serious pollution of Cr(?)in the soil.Cr(?)has the characteristics of high solubility and strong migration.It is easy to migrate from surface soil to deep soil and groundwater.Traditional remediation technology is easy to produce"yellowing"phenomenon,which has become the difficulty of successful remediation of soil chromium pollution.Bioremediation technology has been widely concerned for its low cost and environmental friendliness,but it is difficult for most microorganisms to achieve aerobic/anaerobic Cr(?)continuous bioreduction in surface and deep soil.Therefore,this paper studied the aerobic/anaerobic reduction of Cr(?)by indigenous microorganisms in chromium contaminated soil,and screened a Bacillus sp.Cr02(Bacillus sp.Cr02)which has high tolerance and strong reduction ability to Cr(?)in aerobic/anaerobic environment from the soil.The reduction effect and mechanism of this bacterium to Cr(?)under aerobic/anaerobic conditions were studied The effects of temperature,initial concentration of Cr(?)and coexisting metal ions on the reduction efficiency of Cr(?)were studied,and the remediation effect of Cr(?)on actual Cr contaminated soil was investigated,so as to realize the synergistic remediation of surface and deep Cr contaminated soil.The following valuable research results are obtained in this paper(1)It is clear that indigenous microorganisms have a good reduction effect on Cr(?).The lowest Cr(?)reduction was 387.6 mg/kg in 24 h under aerobic condition;Under anaerobic condition,the lowest Cr(?)reduction amount was 318.4 mg/kg in 36h,and the reduced Cr(?)was mainly residual.(2)The mechanism of bioreduction of Cr(?)by Bacillus sp.Cr02 isolated from indigenous bacteria under aerobic/anaerobic conditions was revealed.The strain could tolerate 800 and 600 mg/L Cr(?)under aerobic and anaerobic conditions,respectively.Chr A plays an important role in the tolerance of Bacillus sp.Cr02 to Cr(?),which reduces the toxicity of Cr(?),and the expression level of chr A is affected by Cr(?).Extracellular enzymes dominated the bioreduction of Cr(?),which could reduce 56%and 48%of Cr(?)(50 mg/L)under aerobic/anaerobic conditions,respectively.Cr(?)can interact with the hydroxyl and carboxyl groups on the cell wall,and can also interact with the amino groups in the amide I band produced by extracellular enzymes,so as to reduce the toxicity of Cr(?)to Bacillus sp.Cr02.(3)The effects of environmental factors such as electron donor,pH,temperature,initial Cr(?)concentration and typical heavy metal ions coexisting in soil on Cr(?)reduction by Cr02 bacteria were elucidated.The best electron donor of Cr02 was waste molasses under aerobic and anaerobic conditions.Under aerobic conditions,Cr(?)could be efficiently reduced by strain Cr02 at 25?35?;Under anaerobic condition,the optimum temperature is 35?.The best growth pH of Cr02 was 9.5.Under aerobic condition,Cr02 could completely reduce 200 mg/L Cr(?)at 60 h;Under anaerobic condition,Cr02 could completely reduce 100 mg/L Cr(?)within 60 h.Cu²⁺(50 mg/L)can promote the reduction of Cr(?),but Cd²⁺and Zn²⁺of 50 mg/l have different inhibitory effects on Cr(?).(4)It is confirmed that Cr02 has a good remediation effect on chromium contaminated soil.After 30 days of remediation,residual chromium was still the main form of soil,and Cr(?)was stable.