Isolation And Characterization Of A Sulfate Reducing Bacterium Strain Cf-k1

It is critical to treat high concentration sulfate wastewater due to its circular pollutionto environment. Compared with other methods, biological treatment has many advantages.Biological desulfurization technology is considered to be the one that shows greatpotential and vast development prospects in the21st century.In this article, a bacteria which could remove the sulfate from wasterwater, wasisolated from sludge of an anaerobic reactor for treating high concentration sulfatewastewater. After diluting sludge sample,63bacteria samples were isolated and cultivatedon the medium which selected3g/L of anhydrous sodium sulfate as the sulfur source. Theconcentration of SO₄^2-in medium was detected by ion chromatography assa whilesulfate-removal was set as filter factor, after three times of the solid-liquid alternatelycultivation, ultimately we selected a strain of bacteria that has stable removal efficiencyfor sulfate, which maximum value can be100%.The strain was identified on the basis of the phenotypic-characteristics andphysiological properties, combined with the analysis of the sequence of16S rDNA. Theresults showed that strain was a gram negative bacteria by the gram experiment; theresults of scanning electron microscopy （SEM） and transmission electron microscopy（TEM） demonstrated the size of bacterial cells was （0.4⁰.5） μm×（1.0².0） μm, with rodshape and flagella; except for urea test, biochemical characteristics of the strain weresimilar to Citrobacter freundii by the test of enterobacteriaceae biochemical identificationtube; the strain was designated strain Cf-k1, which exhibited high levels of99%similarity with Citrobacter freundii strain by DNA sequence alignment in the NCBI.Therefore, the strain Cf-k1was identified as a variant of Citrobacter freundii strain.This study shown that the strain Cf-k1is facultative anaerobic bacteria, underanaerobic condition, the growth pattern of the strains can be described like this:0d¹d,the lag phase;1d³.5d, logarithmic phase;3.5d, strains increment reached its maximum;3.5d⁶.5d, stable period;6.5d, entered the decline phase. The growth pattern is in linewith the rule of general anaerobic growth. With the growth of strains, the pH of thebacterial solution gradually increased, but never higher than pH8; sulfate removal efficiency matched the growth; when the strain was in the logarithmic phase, the removalof sulfate reached the peak, it can transform sulfate into hydrogen sulfide. Addingappropriate concentration of Fe²⁺into the initial medium could promote growth anddesulfurization of the strain, furthermore, FeS precipitation was found adsorbed on the cellwall by TEM, which may render cells dead. Under aerobic conditions, strain can grownormally, but can not remove sulfates.Eight single-factor experiments have been carried out to optimize the cultureconditions for strain Cf-k1under anerobic conditions. Results showed the optimal cultureconditions were:3g/L sodium lactate as carbon source;2g/L ammonium chloride andyeast extract as nitrogen source;3g/L sodium sulphate anhydrous as sulfur source; themost appropriate initial pH of culture media was6.0⁷.0while the optimal temperaturefor growth was35℃; for the sulfate reducing rate, the value could above95%when theoptimum initial sulfate concentration was3g/L; taking sulfate removal amount intoconsideration, the optimum initial sulfate concentration was9g/L while the maximumremoval amount could reach5367mg/L; the best initial COD/SO₄^2-value was setbetween1.26and3.8; the appropriate initial concentration of Fe²⁺was0.8g/L.