• 한국해양학회지
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• v.26 no.1
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• pp.67-76
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• 1991

Masan Bay is infamous for its severe eutrophication, exemplified by frequent red tide incidences and anoxic conditions. We carried out daily observations for 16 days at one site immediately after the summer rainy season in 1988 on the basis that shorter observation intervals be necessary to observe a process with high turnover rate. in spite of the relatively short survey period, we could observe dramatic changes in abundance and composition of the phytoplankton populations. Cell densities and chlorophyll concentrations changed in the magnitude of 70 and 10 times, respectively, Skeletonema costatum, a diatom species, dominated the first peak of phytoplankton biomass and was followed by Prorocentrum minimum, a dinoflagellate species, which occurred dominantly in the second peak after about a week, form the viewpoint of time scale, we suggest that at least a weekly sampling might be appropriate in complex coastal environments as Masan Bay. While stratification enabled high production in the surface layer, it hindered the transport of silicate from bottom to the surface, which in turn limited the prolonged growth of diatoms. Ensued second peaks of silicate and diatom abundance in the surface layer suggest periodic flux of silicate from bottom across the discontinuity driven by tidal currents.

• Journal of Soil and Groundwater Environment
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• v.25 no.1
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• pp.25-36
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• 2020

In a redox transition zone, geochemical reactions are facilitated by active bacteria that mediate reactions involving electrons, and arsenic (As) and iron (Fe) cycles are the major electron transfer reactions occurring at such a site. In this study, the effect of repetitive redox changes on soil bacterial community in As-contaminated soil was investigated. The results revealed that bacterial community changed actively in response to redox changes, and bacterial diversity gradually decreased as the cycle repeated. Proportion of strict aerobes and anaerobes decreased, while microaerophilic species such as Azospirillum oryzae group became the predominant species, accounting for 72.7% of the total counts after four weeks of incubation. Bacterial species capable of reducing Fe or As (e.g., Clostridium, Desulfitobacterium) belonging to diverse phylogenetic groups were detected. Indices representing richness (i.e., Chao 1) and phylogenetic diversity decreased from 1,868 and 1,926 to 848 and 1,121, respectively. Principle component analysis suggests that repetitive redox fluctuation, rather than oxic or anoxic status itself, is an important factor in determining the change of soil bacterial community, which in turn affects the cycling of As and Fe in redox transition zones.

• Journal of Korean Society of Water and Wastewater
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• v.30 no.2
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• pp.187-196
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• 2016

In this study, a newly developed agitator with hydrofoil impeller applied to actual biological process in advanced wastewater treatment plant was evaluated. Several series of experiments were conducted in two different wastewater treatment plants where actual problems have been occurred such as the production of scums and sludge settling. For more effective evaluation, computational fluid dynamics (CFD) and measurements of MLSS (Mixed Liquor Suspended Solids) and DO (Dissolved Oxygen) were used with other measuring equipments. After the installation of one unit of vertical hydrofoil agitator in plant A, scum and sludge settling problems were solved and more than seventy percent of operational energy was saved. In case of plant B, there were three cells of each anoxic and anaerobic tanks, and each cell had one unit of submersible horizontal agitator. After the integration of three cells to one cell in each tank, and installation of one vertical hydrofoil agitator per tank, all the problems caused by improper mixing were solved and more than eighty percent of operational energy was found to be saved. Simple change of agitator applied to biological process in wastewater treatment plant was proved to be essential to eliminate scum and sludge settling problems and to save input energy.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.2
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• pp.161-170
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• 2014

It is essential to decrease energy consumption and excess sludge to economically operate sewage treatment plant. This becomes more important along with a ban on sea dumping and exhaustion of resource. Therefore, many researchers have been study on energy consumption reduction and strategies for minimization of excess sludge production from the activated sludge process. The aeration cost account for a high proportion of maintenance cost because sufficient air is necessary to keep nitrifying bacteria activity of which the oxygen affinity is inferior to that of heterotrophic bacteria. Also, additional costs are incurred to stabilize excess sludge and decrease the volume of sludge. There were anoxic, aerobic, membrane, deairation and concentration zone in this MBR process. Continuous aeration was provided to prevent membrane fouling in membrane zone and intermittent aeration was provided in aerobic zone through ammonia sensor. So, there was the minimum oxygen to remove $NH_4-N$ below limited quantity that could be eliminated in membrane zone. As the result of this control, energy consumption of aeration system declined by between 10.4 % and 19.1 %. Besides, we could maintain high MLSS concentration in concentration zone and this induced the microorganisms to be in starved condition. Consequentially, the amount of excess sludge decrease by about 15 %.

• Journal of Ecology and Environment
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• v.35 no.4
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• pp.279-289
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• 2012

This study conducted a comparative analysis of benthic macroinvertebrate communities in the Fosu and Benya lagoons in Ghana, based on the anthropogenic effect on the two lagoons. Salinity, oxygen, temperature, conductivity, turbidity and pH were measured, invertebrate richness and species densities were determined. The AZTI Marine Biotic Index (AMBI) and multivariate statistics were used to determine the different responses of fauna to pollution. The fauna were categorized into five ecological groups based on the degree of tolerance of the different species to pollution: disturbance-sensitive species; disturbance-indifferent species, disturbance-tolerant species, second-order opportunistic species; and first-order opportunistic species. The Fosu Lagoon supported more pollution tolerant species, whereas the Benya Lagoon had more species that were sensitive to organic enrichment under relatively unpolluted conditions. Chironomus sp., which is adapted to virtually anoxic conditions, was the most abundant in the Fosu Lagoon whereas Nemertea sp. was the most abundant in the Benya Lagoon. The numerical and relative abundance (%) of all 7 taxa in the Fosu Lagoon was 1,359 and 92.35%, respectively. The numerical and relative abundance (%) of all 34 taxa in the Benya Lagoon was 2,459 and 87.52%, respectively. Expectedly, the level of dissolved oxygen in the less saline Fosu Lagoon was higher than that in the more saline Benya Lagoon. The reduced photoperiod and photosynthetic activities of aquatic plants might account for this trend. There is a need to implement comprehensive monitoring and management initiatives for sustaining the ecological health of coastal lagoons in Ghana in order to support the many people that depend upon these ecosystems for their livelihood.

• Microbiology and Biotechnology Letters
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• v.27 no.3
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• pp.252-259
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• 1999

Anoxic sediments collected from Shiwha-ho area were used to find the relationship between the heavy-metal, organic content and anaerobic respiration bacteria by most probable number (MPN) method. Analysis of the sediments showed that COD content was higher in the sediments collected from Ansan-cheon and Shiwha-ho than those collected from sea area nearby. Particularly noticeable was the fact that heavy metal concentration was much higher in the sediments of Shiwha-ho area contaminated by heavy-metal, although they were rich in electron donor and electron acceptor for Fe(III)-reducing bacteria using lactate as an electron donor was in the range of 1.1$\times$106-4.6$\times$107MPNs/ml in the sediments collected from the sea-side of the lake, which were lower in heavy-methal concentration and higher in Fe-Mn content than those from other region. The number of Fe(III)-reducing bacteria using acetate as an electron donor was in the rang eof 4.3$\times$102-8.1$\times$105MPNs/ml in the same sediments. Chromate-reducing bacteria were more populated(4.6$\times$104-8.1$\times$105MPNs/ml) in the sediments contaminated by heavy metals. The number of sulfate-reducing bacteria wee counted in the sediments collected from the more contaminate inner-side than those from the sea-side of the lake.

• Journal of Microbiology and Biotechnology
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• v.22 no.8
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• pp.1155-1160
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• 2012

Sulfur-utilizing autotrophic denitrification relies on an inorganic carbon source to reduce the nitrate by producing sulfuric acid as an end product and can be used for the treatment of wastewaters containing high levels of nitrates. In this study, sulfur-denitrifying bacteria were used in anoxic batch tests with sulfur as the electron donor and nitrate as the electron acceptor. Various medium components were tested under different conditions. Sulfur denitrification can drop the medium pH by producing acid, thus stopping the process half way. To control this mechanism, a 2:1 ratio of sulfur to oyster shell powder was used. Oyster shell powder addition to a sulfur-denitrifying reactor completely removed the nitrate. Using 50, 100, and 200 g of sulfur particles, reaction rate constants of 5.33, 6.29, and $7.96mg^{1/2}/l^{1/2}{\cdot}h$ were obtained, respectively; and using 200 g of sulfur particles showed the highest nitrate removal rates. For different sulfur particle sizes ranging from small (0.85-2.0 mm), medium (2.0-4.0 mm), and large (4.0-4.75 mm), reaction rate constants of 31.56, 10.88, and $6.23mg^{1/2}/l^{1/2}{\cdot}h$ were calculated. The fastest nitrate removal rate was observed for the smallest particle size. Addition of chemical oxygen demand (COD), methanol as the external carbon source, with the autotrophic denitrification in sufficiently alkaline conditions, created a balance between heterotrophic denitrification (which raises the pH) and sulfur-utilizing autotrophic denitrification, which lowers the pH.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.11
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• pp.1141-1145
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• 2005

A contactor coupled sequencing batch reactor composed of pre-anoxic contact zone and intermittently aerated zone was proposed and operated for nitrogen removal. Emphasis was placed on the fact that the contactor can be operated in a rapid reaction mode that results In biological uptake but incomplete metabolism of organic matter. Consequently, 61.2% of the sewage SCOD was adsorbed to activated sludge by 30-minute contact reaction. The specific uptake of organic matter was 22.3 mg SCOD/g MLVSS that enhanced the denitrification efficiency in the following denitrification stage. The removal efficiencies of the organic matter(SCOD) and the total nitrogen(T-N) were 86% and about 60% at the TCOD/TKN ratio as low as 6.0, respectively.

• The Korean Journal of Quaternary Research
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• v.19 no.2
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• pp.35-37
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• 2005

Sediment samples from five stations at the Shihwa Lake sewage outfall, west coast of Korea, were collected to evaluate the effect of the outfall on benthic foraminifera. Heavy metal (Cu and Zn) polluted eastern part of the Shihwa Lake, adjacent to the Shihwa-Banwol Industrial Complexes, shows barren or nearly barren of benthic foraminifera, and the lowest number of species both at the core top and downcore. Excepting for the barren zone, pyritized benthic foraminifera abundantly occur both at the surface and downcore sediments in the western part of the Shihwa Lake, suggesting that foraminiferal disease by anoxic bacteria. Recent intrusion of pollutants from the Shihwa-Banwol Industrial Complexes and adjacent six major streams severely polluted the Shihwa Lake as shown by the low abundance (number/10 g) of benthic foraminifera, low number of A. beccarii, low species diversity, and absence of both Elphidium spp. and ostracodes at the surface sediments compared to the downcore. Except the barren zone, both pyritized and non-pyritized Ammonia beccarii occur dominantly in the surface sediments and downcore. Elphidium spp. (either pyritized or non-pyritized) do not occur in the surface sediments of whole stations. However, they occur from the entire downcore sediments except in the eastern part of Shihwa Lake. Arenaceous foraminifera do not inhabit in the heavily polluted areas as evidenced by the occurrence of relatively deep core depth (11-50 cm). Ostracodes occur at the downcore sediments, but they do not occur at the surface sediments. Ostracodes also do not occur at the heavily polluted areas in the eastern part of the Shihwa Lake both at the surface and downcore sediments, indicating that the abundance of ostracodes also can be used for a pollution indicator.

• The Journal of the Korea Contents Association
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• v.20 no.8
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• pp.674-684
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• 2020

To investigate the differences of bacterial- and archaeal communities depending on kind of wastewater (municipal/livestock) and on treating conditions of basins, sludges were sampled from 10 basins of 3 municipal wastewater treatment plants(WWTP) with A2O and a activated sludge sample from a livestock WWTP. The metagenomic DNAs of the sludge samples were extracted and amplified with primers, 27F/518R for bacteria and Arch519F/A958R for archaea, and pyrosequenced with Roche 454 GS-FLX Titanium. As results, the bacterial communities in basins of municipal WWTPs were quite different from those of livestock WWTP, but within the same municipal WWTP their community structures were similar to each other regardless of different environmental conditions such as O₂. And their archaeal communities resulted from anaerobic·anoxic basins were clustered only within communities originated from the same WWTP. Furthermore Seo-bu WWTP with high bacterial diversity and species richness performed better N/P-removal compared to the orther WWTPs.