SRB와 3가철을 이용한 TCE의 제거에 관한 연구

Abstract

Sulfate Reducing Bacteria(SRB)는 절대 혐기상태에서 살아가며 sulfate를 환원시켜 sulfide를 생성하는 미생물이다. SRB를 이용한 Trichloroethylene(TCE)의 제거에 관한 연구는 오랜 시간동안 진행되어 왔다. SRB를 이용한 TCE의 제거는 친환경적으로 평가되어지나 시간이 많이 걸린다는 단점이 있다. 따라서 본 연구는 TCE로 오염된 퇴적층을 SRB를 이용하여 보다 빠른 속도로 제거할 수 있는 방법을 알아보는 것을 목표로 한다. SRB에 의해 발생하는 sulfide는 높은 환원력으로 유기오염물질을 환원하여 제거시킬 수 있으며 3가철을 2가철로 환원시킬 수 있다. 이러한 두 가지 작용으로 SRB가 성장하는 환경에 3가철과의 공존시 환원에 의한 유기오염물질의 제거의 효율을 높일 수 있다. 본 연구에서는 우선적으로 배치 실험을 통해 TCE에 의한 미생물의 독성을 평가하였으며, SRB에 의해 발생하는 sulfide, ORP, pH, 생균수 등을 측정하여 미생물이 성장하면서 어떠한 변화가 있는지 살펴보았다. 동시에 TCE의 변화를 관찰하여 3가철이 없을 시에 변화를 보았다. SRB의 성장시 발생하는 sulfide의 농도와 TCE의 변화를 측정하여 sulfide에 의한 제거를 확인하였고, sulfide의 농도별로 TCE의 변화를 보았다. 3가철이 있을 시의 sulfide에 의한 2가철의 생성 및 그에 따른 TCE의 제거 기작을 확인 하였고 마지막을 실제 바닷물을 이용하여 이러한 반응이 실제로 자연적으로 발생이 가능한지를 알아보았다.; Sulfate Reducing Bacteria (SRB) is universally distributed in the sediment, specially, in marine environment. SRB reduces sulfate as electron acceptor to hydrogen sulfide in anaerobic condition and theORP range is between -100mV and -200mV. Hydrogen sulfide, which is generated by SRB, is a reducing agent and can effectively reduce the organic and inorganic compounds. Reduced iron also reduces chlorinated organic compounds by reduction. With SRB, therefore, the degradability of organic contaminants by ferrous iron is expected to be enhanced, which is reduced from the ferric iron which is mainly present in sediment. The common occurrence of chlorinated compound such as perchloroethylene (PCE), trichloroethylene (TCE) is largely due to their extensive use of by industry and their resistance to degradation under natural condition. SRB can also cometabolize TCE, but it takes long in the environment. The objectives of this study are: 1) to investigate the biodegradation of TCE by SRB, 2) to investigate the reduction of TCE by hydrogen sulfide generated by SRB growth, 3) to estimate TCE reduction by ferrous iron generated due to oxidation of hydrogen sulfide, and 4) to finally illuminate the interaction between SRB and ferrous iron. To begin with, TCE reduction in the presence of SRB was investigated. The existence of SRB in bacteria and TCE toxic effect on bacteria and TCE reduction were investigated in the absence of iron. The bacteria used in these experiments were cultured in the anaerobic liquid medium from Jungnang Sewage Treatment Plant, in Seoul, South Korea. Measurements of hydrogen sulfide, sulfate, pH, ORP showed increase of hydrogen sulfide and the decrease of sulfate concentration due to bacteria growth only in the presence of bacteria, indicating the existence of SRB in bacteria. Monitoring of TCE concentration, sulfide, and the number of living cell in two conditions, with or without TCE, showed neither TCE toxic effect on bacteria nor TCE reduction by SRB activity. In the condition of keeping hydrogen sulfide which is generated due to SRB activity at concentration 150mg/l, no TCE reduction was observed. These results suggest that in the system with no iron present, no TCE reduction takes place either by SRB or hydrogen sulfide generated from SRB activity. A system with ferric iron present, however, reduce TCE by ferrous iron which is reduced by hydrogen sulfide generated due to bacterial growth.