Won-Seok Kim

Anammox, a reaction in which microorganisms oxidize ammonia under anaerobic conditions, is used in the industry to remove ammonium from wastewater in an environmentally friendly manner. This process does not produce intermediate products such as nitrite or nitrate, which can act as secondary pollutants in soil and water environments. For industrial applications, anammox bacteria should be obtained from the environment and cultivated. Anammox bacteria generally exhibit a slow growth rate and may not produce a large number of cells due to their anaerobic metabolism. Additionally, their habitats appear to be limited to specific environments, such as oxidation-reduction transition zones. Consequently, most of the anammox bacteria that are used or studied originate from marine environments. In this study, anammox bacterial evidence was found in rice paddy soil and cultured under various conditions of aerobic, microaerobic, and anaerobic batch incubations to determine whether enrichment was possible. The anammox-specific gene (hzsA) and microbial community analyses were performed on the incubated soils. Although it was not easy to enrich anammox bacteria due to co-occurrence of denitrification and nitrification based on the chemistry data, potential existence of anammox bacteria was assumed in the terrestrial paddy soil environment. For potential industrial uses, anammox bacteria could be searched for in rice paddy soils by applying optimal enrichment conditions.

Objectives:The objectives of this study is bioremediation and detoxification of arsenite using arsenic resistance system (ars) genotypes of Arsenic Oxidizing Bacteria (AOB) isolated from highly As-contaminated mine.Methods:Bacterial strains that are resistant to arsenic were isolated from the Samkwang mine. The identification of AOB was conducted by analyzing the 16S rRNA gene using universal primers. To determine the genotypes of the arsenic resistance system (ars), specific primers were used for each gene. The extent of arsenic resistance was measured, and the efficiency of arsenite oxidation was assessed through a batch test. Arsenic concentration was measured using ICP-MS.Results and Discussion:The arsenic concentrations at site 1 of the Samkwang mine were found to be 1,322 mg/kg. This concentration is 26.4 times higher than the standard for soil pollution concerns (50 mg/kg) and 8.8 times higher than the standard for soil pollution measures (150 mg/kg). The appropriate remediation is studied such as bacterial remediation. The three efficient AOBs were identified as Agrobacterium tumefaciens EBC-SK1 (MF928870), Ochrobactrum anthrophi EBC-SK4 (MF928873), Ochrobactrum anthrophi EBC-SK12 (MF928881), respectively. The arsenic resistance system (ars) genotype were detected, which is the leader genes of the arsenic oxidation system (arsR and arsD), and the membrane gene (arsB). The arsB is involved in the encoding of the efflux/influx pumping system and moves arsenite into the bacterial cells. Arsenite-oxidizing (aox) genes are activated to oxidize arsenite into arsenate. The AOBs biotransform arsenite to arsenate with the regulation of ars genes, which detoxify highly As-contaminated mine.Conclusion:The AOBs from Samkwang mine are known for their resistance to highly toxic arsenic environments. They play a crucial role in the bioremediation of abandoned mines by transforming As(III) into As(V) through biotransformation.

Objectives : Secondary wastewater is generated as the soil washing process proceeds to restore contaminated soil near the nuclear power plants (NPPs). In this study, we tried to evaluate the possibility of removing radioactive cesium from secondary wastewater through the adsorption process using illite.Methods : To treat radioactive cesium present in wastewater, as an adsorbent, we used illite collected from Yeongdong, Chungbuk, and weathering illite artificially weathered by high temperature and acid treatment (60℃, 0.01 M HCl). Before and after weathering, the adsorption rate of illite at low concentrations of cesium and the desorption rate of adsorbents were compared and evaluated using a 1.5 ppm of competitive potassium ion similar to that of groundwater.Results and Discussion : When the illite was artificially weathered, the amount of frayed edge sites increased as the interlayer ions in the illite eluted. As a result of the adsorption and desorption experiments, it was confirmed that the adsorption rate of weathering illite increased by about 11% in acid condition (pH 3) and about 26% in neutral condition (pH 6.2), and the desorption rate of weathering illite decreased by about 6% in acid and neutral conditions, compared to Yeongdong illite. Yeongdong illite and weathering illite showed higher adsorption rate under neutral condition than acidic condition, because the surface of the illite became negatively charged at high pH so the reactivity with cesium present as a cation increased.Conclusions : The artificial weathering process has improved the performance of illite as an adsorbent. We expect that weathering illite can be used as an effective adsorbent for the removal of radioactive cesium from NPP.

Bismuth-functionalized graphene oxide (Bi-GO) was successfully synthesized and showed both high iodide and iodate removal efficiencies from radioactive wastewater. Batch experiments for kinetic and selectivity tests were performed, respectively. Additional SEM, XRD, FT-IR, and XPS analyses were performed for characterization of a sorbent and bismuth on the GO surface and this confirmed that bismuth on the GO surface reacted with iodine species by surface complexation (or precipitation). Dominant surface species are BiOI and Bi(IO₃)₃ for iodide and iodate removal, respectively. After the selectivity test using a KCl background solution with varying concentrations, Bi-GO still showed higher removal efficiencies (≥95%) for both iodide and iodate than the commercial silver-exchanged zeolite (≥95% for iodide and ≤25% for iodate). Our study suggests the potential application of Bi on graphene-based materials for selective removal of both iodide and iodate from radioactive wastewater.

Batch adsorption, batch diffusion, and flow-through column experiments were conducted using groundwater and fractured rock collected in unsaturated zone to increase our understanding of sorption and transport behavior of radionuclides. Increasing K_d values were observed in the sequence ⁹⁰Sr, ⁹⁹Tc, and ³H regardless of the geological media tested. For all sorbing radionuclides, K_d values for the fracture-filling/coating material were observed to be higher than those for without fracture-filling/coating material regardless of the groundwater. These higher K_d values are the result of zeolite mineral in filling/coating material of fractured rock. The batch diffusion and flow-through column experiments were also conducted using the same fractured rock sample, and the results of diffusion and column experiments showed similar trend of radionuclide sorption and transport to sorption experiment. In this study, sorption K_d of radionuclide was determined and used to increase our understanding of radionuclide retardation through fracture-filling/coating materials.