• 미생물학회지
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• 제33권2호
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• pp.125-130
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• 1997

미생물에 의한 6가이온 크롬의 3가이온으로의 환원은 세균에게 크롬내성을 제공할 수 있는 것으로 알려져 있다. 본 연구에서는 이러한 가설을 확인하기 위하여 크롬오염 토양과 오염되지 않은 토양으로부터 형태적으로 다른 20종의 세균을 순수분리하고 각각의 균주에서 크롬내성과 크롬환원능을 상호 비교하였다. 전자의 공여체로 glucose를 사용했을 때 세포현탁액에 의한 크롬의 환원은 시간당 0.014-0.305mM Cr(VI)의 범위로 관찰되었으며, 액체배지에서 2mM의 크롬에 대한 내성은 크롬을 첨가하지 않은 배지에서 배양한 경우와 혼탁도를 비교한 결과 전혀 저해를 받지 않는 경우부터 93.4%의 성장저해를 받는 경우까지 다양하게 관찰되었다. 이러한 결과로부터 상관관계를 분석한 결과 크롬내성과 크롬환원은 전혀 상관이 없는 것으로 계산되었다. 한편 군집수준에서의 크롬내성비교는 크롬오염 토양과 오염되지 않은 토양에서 각각 19.1%와 0.4%로 나타나 크롬의 존재는 내성균주의 선택적 성장을 유도하는 것으로 밝혀졌다. 그러나 이때 획득된 크롬에 대한 내성은 크롬의 환원에 의해서 제공되는 것이 아님을 상관관계 분석으로부터 알 수 있었다.

• Journal of Microbiology and Biotechnology
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• 제23권8호
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• pp.1123-1132
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• 2013

The removal of toxic Cr(VI) by microorganisms is a promising approach for Cr(VI) pollution remediation. In the present study, four indigenous bacteria, named LY1, LY2, LY6, and LY7, were isolated from Cr(VI)-contaminated soil. Among the four Cr(VI)-resistant isolates, strain LY6 displayed the highest Cr(VI)-removing ability, with 100 mg/l Cr(VI) being completely removed within 144 h. It could effectively remove Cr(VI) over a wide pH range from 5.5 to 9.5, with the optimal pH of 8.5. The amount of Cr(VI) removed increased with initial Cr(VI) concentration. Data from the time-course analysis of Cr(VI) removal by strain LY6 followed first-order kinetics. Based on the 16S rRNA gene sequence, strain LY6 was identified as Pseudochrobactrum asaccharolyticum, a species that had never been reported for Cr(VI) removal before. Transmission electron microscopy and energy dispersive X-ray spectroscopy analysis further confirmed that strain LY6 could accumulate chromium within the cell while conducting Cr(VI) removal. The results suggested that the indigenous bacterial strain LY6 would be a new candidate for potential application in Cr(VI) pollution bioremediation.

• Journal of Microbiology and Biotechnology
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• 제22권4호
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• pp.547-554
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• 2012

Chromium is generated from several industrial processes. It occurs in different oxidation states, but Cr(III) and Cr(VI) are the most common ones. Cr(VI) is a toxic, soluble environmental contaminant. Some bacteria are able to reduce hexavalent chromium to the insoluble and less toxic Cr(III), and thus chromate bioremediation is of considerable interest. An indigenous chromium-reducing bacterial strain, Rb-2, isolated from a tannery water sample, was identified as Ochrobactrum intermedium, on the basis of 16S rRNA gene sequencing. The influence of factors like temperature of incubation, initial concentration of Cr, mobility of bacteria, and different carbon sources were studied to test the ability of the bacterium to reduce Cr(VI) under variable environmental conditions. The ability of the bacterial strain to reduce hexavalent chromium in artificial and industrial sewage water was evaluated. It was observed that the mechanism of resistance to metal was not due to the change in the permeability barrier of the cell membrane, and the enzyme activity was found to be inductive. Intracellular reduction of Cr(VI) was proven by reductase assay using cell-free extract. Scanning electron microscopy revealed chromium precipitates on bacterial cell surfaces, and transmission electron microscopy showed the outer as well as inner distribution of Cr(VI). This bacterial strain can be useful for Cr(VI) detoxification under a wide range of environmental conditions.

• Journal of Microbiology and Biotechnology
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• 제22권5호
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• pp.690-698
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• 2012

Cr-B2, a Gram-negative hexavalent chromium [Cr(VI)] reducing bacteria, was isolated from the aerator water of an activated sludge process in the wastewater treatment facility of a dye and pigment based chemical industry. Cr-B2 exhibited a resistance for 1,100 mg/l Cr(VI) and, similarly, resistance against other heavy metal ions such as $Ni^{2+}$ (800 mg/l), $Cu^{2+}$ (600 mg/l), $Pb^{2+}$ (1,100 mg/l), $Cd^{2+}$ (350 mg/l), $ZN^{2+}$ (700 mg/l), and $Fe^{3+}$ (1,000 mg/l), and against selected antibiotics. Cr-B2 was observed to efficiently reduce 200 mg/l Cr(VI) completely in both nutrient and LB media, and could convert Cr(VI) to Cr(III) aerobically. Cr(VI) reduction kinetics followed allosteric enzyme kinetics. The $K_m$ values were found to be 43.11 mg/l for nutrient media and 38.05 mg/l for LB media. $V_{max}$ values of 13.17 mg/l/h and 12.53 mg/l/h were obtained for nutrient media and LB media, respectively, and the cooperativity coefficients (n) were found to be 8.47 and 3.49, respectively, indicating positive cooperativity in both cases. SEM analysis showed the formation of wrinkles and depressions in the cells when exposed to 800 mg/l Cr(VI) concentration. The organism was seen to exhibit pleomorphic behavior. Cr-B2 was identified on the basis of morphological, biochemical, and partial 16S rRNA gene sequencing chracterizations and found to be Acinetobacter sp.

• 공업화학
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• 제9권7호
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• pp.1036-1042
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• 1998

소수성실관막을 이용하여 수용액 중의 Cr(VI)을 TDA로 추출하고, 이를 NaOH 수용액으로 회수하였다. 역추출공정에서의 물질전달속도는 추출공정에 비해 작았으며, 이러한 결과는 소수성막의 내부를 유기상이 흐르게 되면 추출과정에서는 무시할 수 있었던 막저항이 작용하기 때문이라 판단된다. 막수량을 달리한 4개의 막모듈(60, 100, 150, 300가닥)을 제작하였으며, 각 모듈에 대해 수용상 및 유기상의 유량이 물질전달속도에 미치는 영향에 대해서도 검토하였다. 이 실험으로부터 소수성막을 이용한 추출공정에서는, 막내부를 흐르는 수용상의 유량이 물질전달속도에 큰 영향을 주었으나 유기상 유량의 영향은 미약하다는 것을 알 수 있었다. 반면, 역추출공정에서의 물질전달속도는 수용상(회수액)유량에도 유기상(Cr-TDA 착화합물)의 유량에도 영향을 받지 않음을 알 수 있었다.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.271-272
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• 2006

Zinc confers high corrosion resistance by acting as a sacrificial anode, and a zinc coating improves the appearance of steel. Chromate conversion coating (CCC) films are still one of the most efficient surface treatments for steel. Although such films can self-repair via the dissolution of Cr(VI), dissolved Cr(VI) have adverse effects on humans, and the environment. Therefore, we examined the corrosion protection property and morphology of colloidal silica conversion films as an alternative to CCC films. The corrosion behavior was investigated in 3% NaCl solution using electrochemical techniques, including electrochemical impedance spectroscopy, open circuit potential, and the salt spray test(SST). Corrosion was implied by the appearance of red rust on the specimen surface. In corrosion resistance at 3% NaCl solution, red rust appeared at 15-20, 55-70, and 83-98 days on Zn-electroplated steel, colloidal silica conversion-coated specimens, and CCC-coated specimens, respectively. In the salt spray test, the colloidal silica film provided better corrosion protection than CCC films, i.e., red rust appeared at 96 hours on the Zn-electroplated steel sheet, at 432 hours with the CCC films, and at 888 hours with silica conversion coating.