• Journal of Environmental Health Sciences
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• v.40 no.2
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• pp.88-97
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• 2014

Objectives: The aim of this study was to evaluate the occurrence of microbiological contamination of kitchen utensils and environments of food service operations at university located in Seoul, Korea. Methods: We collected swab samples from the surfaces of knives, chopping boards, floors, and drains, as well as drinking water and airborne bacteria samples from 20 food service operations. Three bacterial indicators and five food poisoning bacteria were measured quantitatively and qualitatively, respectively. We used selective culture media and the PCR assay targeting 16S rRNA gene for the microbiological analysis. Results: We detected bacterial indicators on knives or chopping boards in eight different food service operations and, three food service operations (I, M, and O) showed more than 3 log colony forming units $(CFU)/100cm^2$ on their knives, significantly higher than the others. The levels of bacterial indicators on the floors and drains in the cooking areas were much higher than those on the cooking utensils. S. aureus was detected on 10 floors and 8 drains. Culturable bacteria were identified in 5 drinking water samples, and food service operation B ($431.1CFU/m^3$) and C ($551.2CFU/m^3$) showed more than $400CFU/m^3$ of total airborne bacteria. Conclusions: These results suggest that some of food service operations in this study may require additional investigation to secure the microbial safety of cooking environments. In addition, further actions including hygiene education for employees and proper guidelines to maintain clean cooking environments should be prepared.

• Korean Chemical Engineering Research
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• v.54 no.6
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• pp.854-862
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• 2016

As the demand for a clean energy to replace fossil fuel being depleted increases, hydrogen energy is considered as a promising candidate for future energy source. Water electrolysis which produces hydrogen has high energy efficiency and stability but still has a large overpotential for oxygen evolution reaction (OER). In this study, $Co_3O_4$ catalysts with different morphology were prepared by spray pyrolysis from solutions which contain Co precursor and various organic additives (urea, sucrose, and citric acid), followed by post heat treatment. For the catalysts synthesized, X-ray diffraction (XRD) measurements were performed to identify their crystal structure. Morphology and surface shape of the catalysts were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Surface area and pore volume were examined by nitrogen adsortpion & desorption tests and X-ray photoelectron spectroscopy (XPS) was conducted to confirm nitrogen doping. Linear sweep voltammetry (LSV) was carried out to investigate OER activity of $Co_3O_4$ catalysts. As a result, bare-$Co_3O_4$ which has high surface area and small particle size determined by spray pyrolysis showed high activity toward OER.

• KSBB Journal
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• v.20 no.6
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• pp.393-400
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• 2005

Hydrogen($H_2$) as a clean, and renewable energy carrier will be served an important role in the future energy economy. Several biological $H_2$ production processes are known and currently under development, ranging from direct bio-photolysis of water by green algae, indirect bio-photolysis by cyanobacteria including the separated two stage photolysis using the combination of green algae and photosynthetic microorganisms or green algae alone, dark anaerobic fermentation by fermentative bacteria, photo-fermentation by purple bacteria, and water gas shift reaction by photosynthetic or fermentative bacteria. In this paper, biological $H_2$ production processes, that are being explored in fundamental and applied research, are reviewed.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.12
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• pp.978-981
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• 2013

This study selected representative popular bowls used in daily life and laboratory and investigated the amount of residual surfactant resided in the bowls that were dish-washed. The bowls were washed by a scourer soaking 8 mL-detergent and then rinsed by flowing water for 7 or 15 seconds. One hundred milliliter of distilled water was placed in the washed-bowls to extract residual surfactant on the bowl surface and then analysed. All washed-bowls included residual surfactant after 7 second-rinsing. Residual surfactant concentrations in Ttukbaegi (earthen bowl), flying pan, glass bowl, and plastic bowl were 4.68, 1.22, 0.57, and 0.25 mg/L, respectively. However, the 15 second-rinsing showed that surfactant was detected only in Ttukbaegi and other bowls were clean. The results showed that surfactant would reside on the porous or rough surface of the bowl even after final rinsing. This study imply that all bowls and glasses should be throughly rinsed after detergent-washing to reduce continuos ingestion. Furthermore, residual surfactant in the glassware of laboratory may significantly affect experiment results.

• Journal of the Korean association of regional geographers
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• v.13 no.2
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• pp.187-200
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• 2007

This study look into the 3 stages which is distinguished by the usage of human in Man-Kyeong river. 'A nature based usage stage' is acknowledge the river itself and used only the tributary and built reservoir in a small scale from ancient to 1910s. 'A human based usage stage' is built the large scale reservoir at upper stream area and make the artificial waterway from 1920s. And the main stream is remodeled to protect the flood and get the agricultural land. 'A human and nature integration stage' is the main stream has a role not only the spill way but also clean water for inhabitants does together with river. The role and meaning of river is given newly. The development of technique and increase the need of the human is required the change in the role and meaning of river. The river is natural existence as it is, but the meaning and role is given by the human. Also it accompanied the change of the landscape in neighbor region. The natural river is controled the human life in the past, but it changed to social existence which is given the role and meaning by the human now.

• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.2
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• pp.92-103
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• 1993

A sunday system with a horizontal bin-type composter was constructed and operated to evaluate its composting performance for four days for each test in October, 1992. A sundry system is one of popular systems for composting livestock manure, of which main benefit is to utilize unlimited, clean, and free solar radiation. A rectangular concrete bin(composter) with dimension of 300cm(length) X90cm(width) X60cm(height) was bedded alternatively with four lanes of aeration pipes and heating pipes, and was insulated at three walls with 50mm styrofoam. Each aeration pipe of a diameter of 25mm had 4mm perforated holes at every 15cm longitudinally, and supplied air of about 2m$^3$/min to the composter to maintain aerobic condition . A stirrer rotating at 1 rpm made one round trip every 20 minutes on the conveying chain along the the length of the composter. Five tests (Test 1~Test 5) were implemented to evaluate the composting effectiveness of a sundry system with a horizontal bin-type composter. Treatments of two levels of the mixture ratio of swine manure and paper sludge cakes(manure : paper sludge cakes= 1 : 4 and 1 : 2) and two levels of the water content(W/C ; 70% and 50%) were made to test the significance of the physicochemical properties for decomposition of the mixture materials. Temperature, C/N ratio, water content, microbial activity of the composting materials were taken measurements to evaluate its performance with the lapse of composting time for tests. A small-scale sundry system with a bin-type composter did not appear to be an appropriate system for composting livestock manure. Since heat generation by the composting materials could not overcome heat loss due to areation in a small-scale composter, a proper thermal enviroment could not be maintained to propagate massively thermopilic microorganism relatively in a short period of time. Different from the result of Chol et al.(1992) 6), a temperature variation of the composting materials did not show the peak clearly and C/N ratio didn't lower with time as expected. Mesophilic microoragnism seemed to play an important role for decomposition of the mixture materials. A sundry system with a bin-type composter may be good for a large-scale livestock farm household which may produce enough animal manure. Therefore a decision should be made very carefully to choose a system for composting livestock waste.

• Journal of Korean Society of Forest Science
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• v.101 no.1
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• pp.130-137
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• 2012

This study has conducted to develop new gabion wall systems with vegetation base materials for stream bank stability and rapid rehabilitation. Vegetation base materials are primarily compounded with fine soil, organic composts and peat moss as plant fibers, a water retainer and a soil improver. Normally gabion wall systems resist the lateral earth pressures or stream power by their own weight. Therefore, fill material must have suitable weight, compressive strength and durability to resist the loading, as well as the effects of water and weathering. In this project, 100 to 200-mm clean, hard stones are basically specified, and about 50-mm rubbles are also used. Test application of new gabion wall system carried out in the stream bank of a small stream in the Gwangreung experimental forest, belonging to Korea Forest Research Institute (KFRI) in December 16th, 2006. As a result of the analysis of hydraulic stability of new gabion wall system, gabion wall system has highest threshold shear stress when the gabion wall covered by vegetation. New gabion wall system is highly resistant to sliding and overturning because safety coefficients exceed 1.5. As a result of term of slope stability analysis of new gabion wall system by Bishop and Fellenius methods, stability of stream bank was highly increased after the construction of gabion wall. Therefore, new gabion wall system is effective to stabilize unstable stream bank.

• Restorative Dentistry and Endodontics
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• v.21 no.2
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• pp.602-618
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• 1996

The purpose of this study was to investigate the effect of acid treatment of fluoride applied dentin surface with various concentrations of phosphoric acid for various periods of time on dentin bonding. Dentin specimens prepared from freshly extracted bovine mandibular anterior teeth were divided into fluoridated and nonfluoridated groups. Specimens of nonfluoridated group were pretreated with 10% phosphoric acid for 15 seconds. Those of fluoridated groups were treated with 2% sodium fluoride or 2% stannous fluoride solution for 5 minutes and stored in $37^{\circ}C$ distilled water for 3 days, followed by phosphoric acid treatment. The concentrations of phosphoric acid were 10%, 32% or 50% and the treatment periods of time were 15, 30 or 60 seconds. All the specimens were bonded with All Bond$^{(R)}$ 2 and Bisfil$^{TM}$ composite resin. After bonded specimens were stored in $37^{\circ}C$ distilled water for 24 hours, tensile bond strengths of each specimens were measured and the pretreated dentin and the fractured dentin surfaces were examined under the scanning electron microscope. The results were as follows : The tensile bond strengths from the fluoridated groups were significantly lower than those from the nonfluoridated group when the concentrations of phosphoric acid and the treatment periods of time were equal in all the groups (p<0.05). In general, the higher the concentration of phosphoric acid and the longer the treatment period of time for acid etching on the fluoride applied dentin surface, the higher were the bond strength values. Recovery of bond strength of the dentin bonding agent was better in the NaF applied group than in the $SnF_2$ applied one. SEM findings of NaF applied and $SnF_2$ applied dentin surfaces demonstrated reaction product-covered and partially or completely obstructed dentinal tubules. SEM findings of dentin surfaces fluoridated for 5 minutes followed by etching showed wider tubular openings and more clean dentin surfaces when dentin was etched with higher concentration of phosphoric acid for longer period of time. On the SEM observations of the fractured dentin-resin interface, the etched specimens of fluoridated group showed an adhesive failure mode when the concentration of phosphoric acid and the treatment period of time were same as in the nonfluoridated group. As the concentration of phosphoric acid and the treatment period of time increase during acid etching, the cohesive failure area increased. However, excessive acid etching caused adhesive failure.

• Membrane Journal
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• v.31 no.2
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• pp.101-119
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• 2021

The demand for clean water is virtually present in all modern human societies even as our society has developed increasingly more advanced and sophisticated technologies to improve human life. However, as global climate change begins to show more dramatic effects in many regions in the world, the demand for a cheap, effective way to treat wastewater or to remove harmful bacteria, microbes, viruses, and other solvents detrimental to human health has continued to remain present and remains as important as ever. Well-established synthetic membranes composed of polyaniline (PANI), polyvinylidene fluoride (PVDF), and others have been extensively studied to gather information regarding the characteristics and performance of the membrane, but recent studies have shown that making these synthetic membranes conductive to electrical current by doping the membrane with another material or incorporating conductive materials onto the surface of the membrane, such as allotropes of carbon, have shown to increase the performance of these membranes by allowing the adjustability of pore size, improving antifouling and making the antibacterial property better. In this review, modern electrically conductive membranes are compared to conventional membranes and their performance improvements under electric fields are discussed, as well as their potential in water filtration and wastewater treatment applications.

• Korean Journal of Ichthyology
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• v.31 no.1
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• pp.16-22
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• 2019

Investigations on the study of the distribution aspects and extinction threat evaluation of the Korean endemic species, Iksookimia pacifica were done from 2017 to 2018 in Korea. During the study period, the samples of I. pacifica were collected in 17 streams, 46 sites (from Baebongcheon Stream of Goseong-gun to Gunsuncheon Stream of Gangneung-si) among the noted 33 streams and 104 sampling sites investigated. The population size of I. pacifica was relatively large in streams such as Bukcheon, Baebongcheon, Hwasangcheon, Cheonjincheon, Ohhocheon Stream etc., but the population size was small in streams such as Sacheoncheon, Namcheon, Gangneung Namdaecheon Stream etc. The main habitat of I. pacifica was the downstream pool of clean water with slow velocity and sand bottoms, and their sensibility was estimated to be due to river work and water pollution. Comparing the previous records of the appearance of I. pacifica, they were first seen in Sampocheon Stream, but they did not appear in Jusucheon, Jeoncheon, Samcheok Osipcheon Stream. Given this evidence as noted for the 19.5% reduction in occupancy within 3 generations, in small appearance range ($1,343km^2$) and small occupancy area ($184km^2$), the number of locations were many (18) and the population was relatively large within the range of habitat. Therefore, I. pacifica is now considered a Near Threatened (NT) based on the IUCN Red List categories and criteria.