Isolation And Characterization Of SRB Strain With Its Application In The Treatment Of Acidic Wastewater With Cd Contamination

Acidic wastewater with Cd contamination with high acidity,high Cd²⁺concentration and high sulfate concentration is discharged uncontrollably in mining,metal smelting and electroplating industries,which makes water or soil acidification and heavy metal Cd pollution more and more serious in China.Acidic and high sulfate wastewater can poison water or soil,destroy ecosystem and endanger living environment of organisms.Cd has long-term latency and high carcinogenicity,endangering the health of organisms and human beings.Because of the complexity of acid wastewater containing cadmium,the traditional treatment methods have the problems of low efficiency,high cost and secondary pollution,so it is urgent to find an efficient,low cost and environmental protection treatment method.At present,the biological method represented by sulfate-reducing bacteria has attracted much attention as a new practical technology.Because of its special metabolic pathway,SO₄^2-can be reduced to H₂S and OH^-,H₂S dissolved in water combined Cd²⁺and turned into CdS precipitation,achieving simultaneous desulfurization(SO₄^2-),cadmium(Cd²⁺)removal and increasing pH value without secondary pollution.On the basis of current research,the main contents and results of this study are as follows:?1?An acid-resistant sulfate-reducing bacteria SRB1 was isolated from soil and activated sludge.It was identified as Desulfovibrio strain.Its lowest tolerant pH value,maximum Cd²⁺concentration,SO₄^2-concentration and salinity were 3.7,40 mg/L,1500 mg/L and 1%,respectively.The inhibitory concentrations of Cu²⁺,Mn²⁺,Co²⁺,Zn²⁺,Pb²⁺,Hg²⁺,Cr³⁺,Ni²⁺were 10,30,2,20,25,5,30,15 mg/L,respectively.And the inhibitory action sequence was Co²⁺>Hg²⁺>Cu²⁺>Zn²⁺>Ni²⁺>Pb²⁺>Mn²⁺>Cr³⁺.Under the optimum experimental conditions,the pH value can be increased from 6.0to about 7.5,the ORP value,Cd²⁺and SO₄^2-concentration can be reduced from-110mV,30 mg/L,1500 mg/L to-330 mV,2.45 mg/L and 550 mg/L,respectively.The desulfurization and cadmium removal rates were 63.3%and 91.8%.?2?The immobilization of strain SRB1 was researched in this study.Under the optimum experimental conditions,the adsorption rate of immobilized pellets for Cd²⁺was 95.4%,and the adsorption capacity was 11.87 mg/g,which accorded with the pseudo-second-order kinetic equation model,the model's validation values?Qe,cal?was15.31 mg/g.The isothermal adsorption process accorded with Langmuir equation,and the maximum adsorption capacity?Qmax?predicted 44.05 mg/g.The adsorption process was contained mainly chemical adsorption and many influencing factors affected it.The apparent Gibbs function changes?G⁰?was a negative value,which showned the adsorption was a spontaneous process.?3?The experimental device of adsorption-immobilization SRB1 culture-SRB1secondary culture intermittent operation was used to treat simulated acidic wastewater containing cadmium,and the Cd²⁺concentration of effluent was almost decreased to 0.The desulfurization and cadmium removal rates were 70.8%and 95.2%after immobilized SRB1 was cultured at pH value,SO₄^2-concentration and Cd²⁺concentration was 6.0,1500.2 mg/L and 39.6 mg/L,respectively.Moreover,the reaction rate of Cd²⁺precipitation and that of SO₄^2-indicated 1 mg Cd²⁺could be precipitated when SRB1 reduced 35.5 mg SO₄^2-.?4?SRB1 cells were used as nuclei to form large particles and precipitate or crystallize.SEM proved the precipitates enwrapped the SRB1 cells.pH value and initial Cd²⁺concentration affected the morphology,size and composition of the precipitates,which contained crystalline CdS.