| Summary: | 碩士 === 國立中山大學 === 環境工程研究所 === 103 === In recent years, soil and groundwater contaminated by heavy metals (e.g., arsenic, cadmium, mercury, chromium, copper, nickel, lead, zinc) have become a serious environmental problem. In this study, microcosm experiments were conducted using enriched contaminated groundwater as the inocula to evaluate the feasibility of applying the reduction process to remediation chromate contaminated groundwater. Each microcosm contained enriched bacteria broth, cromate, groundwater, and nutrient broth. Kill and live control microcosms were also prepared for comparison. Molecular biotechnology methods including polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE), and biological sequencing analysis were applied to determine the dominant bacteria and microbial diversity. Results show that up to 92% of hexavalent chromium (HCr) reduction efficiency was observed after 137 days of incubation. The pH ranged from 7.5 to 9.0. The reduction of total organic carbon (TOC) indicates that the carbon source was consumed by the bacteria. Slight increase of the oxidation-reduction potential (ORP) was observed during the operation. This could be due to the occurrence of microbial reduction of hexavalent chromium, which produced oxidizing substances (reactive oxygen species, ROS). Thus, oxygen-containing species (e.g., oxygen ion (oxygen ion, O2-) and hydrogen peroxide (H2O2)) might damage the anaerobic bacteria cell body and resulted in the inhibition of biological process. Results also confirmed that the occurrence of biological precipitation and biocolloid examined by environmental scanning microscope/X ray microanalysis (SEM/EDAX). Results from the microbial diversity analyses show that the acclimated bacteria could resist high cromate concentration with high cromate reduction ability. Results from the DGGE and sequence analyses show that there were 16 dominant intrinsic bacteria had the chromate reduction ability. The α-proteobacteria contained Alpha proteobacterium, Acetobacteraceae bacterium, Caulobacterales bacterium, Enterobacter sp. and Rhodospirillales bacterium. The β-proteobacteria contained Beta proteobacterium, Dechloromonas sp., Propionivibrio sp., Rhodocyclaceae bacterium, Rhodocyclales bacterium, Methyloversatilis sp., and Nitrosomonadales bacterium. The γ-proteobacteria contained Enterobacteriales bacterium, Gamma proteobacterium, Prokaryote bacterium, and Psychrobacter sp. The isolated chromate reducing bacteria (CRB) could grow well under the high chromate conditions. Moreover, CRB could effectively reduce the chromate toxicity after the reduction process. The biological reduction process meets the requirement of green remediation.
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