수용액 내 세슘 제거를 위한 R. erythropolis 흡착 공정 및 축적 위치 규명 = Identification of R. erythropolis bioadsorption process and cesium accumulation location

다국어 초록 (Multilingual Abstract)

The risk of nuclear power plant accidents and the generation of by-products (wastewater) from the plants has heightened the importance of disposing of radioactive materials. We explored the use of Rhodococcus erythropolis as an eco-friendly biosorbent to remove cesium, a representative radioactive material. Bacteria were inoculated into BS medium containing 0.0, 1.0, 5.0, 10.0, 30.0, and 50.0 mM cesium. Bacterial growth and the appropriate cesium concentration were evaluated. Bacteria were viable between 0.0 and 10.0 mM cesium. The maximum removal efficiencies in BS media containing 0.1, 1.0 and 5.0 mM cesium were 84.29, 23.33, and 10.04%, respectively.
Cesium removal efficiencies markedly decreased when bacteria were in the stationary phase of growth. Two methods are posed to prevent the decreased efficiency. The first method is to immobilize R. erythropolis on a hydrogel and recover it when maximum removal efficiency is expected. The second method is to change the medium composition to find suitable conditions that do not decrease removal efficiency. In the first approach, immobilized bacteria removed up to 47.89% of cesium at 120 hours following inoculation. Recovering the hydrogel after removal of cesium prevented cesium leakage and facilitated bacteria recovery. Cesium removal by bacteria was evaluated different amounts of ions using distilled water and LB medium. In distilled water, the cesium removal efficiency of R. erythropolis increased and remained flat for 2 weeks thereafter with increasing the inoculum amount. However, in the LB medium, various ions competed with cesium and were not adsorbed to bacteria, and the removal rate was as low as 11%.
FE-TEM visually confirmed cesium accumulation in R. erythropolis. The accumulation was extensive in an inner compartment termed acidocalcisomes. Acidocalcisomes can also store phosphorus and regulate pH and osmosis. FE-SEM, FT-IR, and XRD analyses compared bacterial changes after cesium removal. FE-SEM analyses of samples containing 0.0, 0.1, 1.0, and 5.0 mM cesium revealed increasing cell length with increasing cesium concentration. FT-IR and XRD analyses confirmed various bacterial changes after cesium removal.
The collective results indicate that if the maximum cesium removal efficiency and conditions are improved, the use of bacteria to treat radioactive wastewater generated in nuclear power is feasible, as is remediation of environments contaminated with radioactive cesium.

목차 (Table of Contents)

• 1. 서론 1
• 1.1. 이론적 배경 1
• 1.2. 원자력 발전사고 3
• 1.2.1. 후쿠시마 제1 원자력 발전 사고 3
• 1.2.2. 체르노빌 원자력 발전 사고 5
• 1.3. 방사성 물질이 인체에 미치는 영향 7
• 1.4. 세슘 8
• 1.5. 생체 흡착법 9
• 1.6. 미생물 흡착 메커니즘 10
• 1.7. 연구 목적 12
• 2. R. erythropolis를 이용한 세슘 제거 14
• 2.1. 문헌연구 14
• 2.2. 박테리아 생장성 평가 17
• 2.2.1. 실험 재료 및 방법 17
• 2.2.2. 실험 결과 및 고찰 19
• 2.3. 세슘 제거 효율 평가 21
• 2.3.1. 실험 재료 및 방법 21
• 2.3.2. 실험 결과 및 고찰 22
• 2.4. 결론 25
• 3. 세슘 제거율 감소 해결 방안 26
• 3.1. 문헌연구 26
• 3.1.1. 미생물 겔 고정화 26
• 3.1.2. 세슘 이온의 화학적 거동 27
• 3.2. 박테리아 겔 고정화 28
• 3.2.1. 실험 재료 및 방법 28
• 3.2.2. 실험 결과 및 고찰 30
• 3.3. 배지 조성에 따른 세슘 제거율 33
• 3.3.1. 실험 재료 및 방법 33
• 3.3.2. 실험 결과 및 고찰 33
• 3.4. 결론 35
• 4. 박테리아 내 세슘 축적 위치 파악 36
• 4.1. 실험 재료 및 방법 36
• 4.2. 실험 결과 및 고찰 37
• 5. 세슘 제거 전·후 박테리아 비교 45
• 5.1 SEM 45
• 5.2 FT-IR 48
• 5.3 XRD 50
• 6. 결론 52
• 7. 참고 문헌 54
• 8. 영문 초록 68