• Korean Chemical Engineering Research
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• v.51 no.6
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• pp.666-670
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• 2013

Recovery method of silicon wafer from defective products generated from manufacturing process of silicon solar cells was studied. The removal effect of the N layer and antireflection coating (ARC) of the waste solar cell were investigated at room temperature ($25^{\circ}C$) by variation of concentration of $H_3PO_4$, $NH_4HF_2$, and concentration and types of chelating agent. Removal efficiency was the best in the conditions; 10 wt% $H_3PO_4$ 2.0 wt% $NH_4HF_2$, 1.5 wt% Hydantoin. Increasing the concentration of $H_3PO_4$, the surface contamination degree was increased and the thickness of the silicon wafe became thicker than the thickness before surface treatment because of re-adsorption on the silicon wafer surface by electrostatic attraction of the fine particles changed to (+). The etching method by mixed solution of $H_3PO_4$-$NH_4HF_2$-chelating agents was expected to be great as an alternative to conventional RCA cleaning methods and as the recycle method of waste solar cells, because all processes are performed at room temperature, the process is simple, and less wastewater, the removal efficiency of the surface of the solar cell was excellent.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.06a
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• pp.72-80
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• 2004

Electrolytic dissolution study was carried out to evaluate the applicability of electrochemical decontamination process using a neutral salt electrolyte as a decontamination technology for the recycle or self disposal with authorization of large amount of metallic wastes contaminated with uranium compounds generated by dismantling a retired uranium conversion plant using SUS-304 and Inconel-600 specimen as the main materials of internal system components of the plant. The effects of type of neutral salt as an electrolyte, current density, and concentration of electrolyte on the dissolution of the materials were evaluated. On the basis of the results obtained through the basic inactive experiments, electrochemical decontamination tests using the specimens contaminated with uranium compounds such as $UO_2$, AUC (ammonium uranyl carbonate) and ADU (ammonium diuranate) taken from an uranium conversion plant were peformed in $Na_2SO_4$ and $NaNO_3$ solution. It was verified that the electrochemical decontamination of the dismantled metallic wastes was quite successful in $Na_2SO_4$ and $NaNO_3$ neutral salt electrolyte by reducing $\beta$ radioactivities below the level of self disposal with authorization within 10 minutes regardless of the type of contaminants and the degree of contamination.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.4
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• pp.275-286
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• 2014

This study evaluated the evolution stage and origin of chemical components of 12 boreholes at crystalline bedrock using multivariate statistical and groundwater quality analyses. Groundwater types are mostly belonged to Na(Ca)-$HCO_3$ and Ca-$HCO_3$ types, indicating that directly reaction of cation exchange ($Ca^{2+}{\rightarrow}Na^+$) prevailed. The degree of groundwater evolution is included the range from low to intermediate stage based on field and laboratory analytical conditions. As a result of multivariate statistical analysis, a typical indicator of groundwater contamination, $NO_3$-, has the positive correlation with $Na^+$ and $Cl^-$. The origin of sea spary ($Cl^-$) has the positive correlation with $Na^+$, $SO{_4}^{2-}$, $Mg^{2+}$, and $K^+$, while not correlation with $Ca^{2+}$, $Fe^{2+}$, $HCO_3{^-}$, $F^-$, and $SiO_2$. The concentration of $Cl^-$ and $NO_3{^-}$ belongs to general quality of groundwater and not exceeds over the Korean standard for drinking water. And the negative values of saturation index of minerals are calculated with chemical components in groundwater. Therefore, most of chemical components of groundwater in the study area are originated from natural process between rock and groundwater, whereas some of components are derived from sea spary and anthropogenic sources related to agricultural activities.

• Economic and Environmental Geology
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• v.37 no.3
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• pp.335-345
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• 2004

Total and extractable contents of heavy metals were measured in sediment and seafood from Bukhang and Boggil-ri tidal flats along the Mokpo coastal area, south-western part of Korean peninsular in order to assess the degree of metal pollution, metal bioavailability and metal hioaccumulation. The metal concentrations, except Pb were found to be greater than the background concentrations of sediments indicating the progress of cumulative contamination by anthropogenic origin of metals. The order of extractable metal concentrations in sediments were Mn(32-53 mg/kg)＞Zn(14-42 mg/tg)＞Cu(2.5-17.0 mg/kg)＞Pb(2.4-6.8 mg/kg)＞Cd(0.5-0.7 mg/kg). However, the amount of metals associated with extractable fraction of sediments were significantly high in Bukhang relative to Boggil-ri. Significant bioaccumulation of all metals, except Pb were observed in seaweed and benthos. The order of bioaccumulation of metals were: in concentration; all biota commonly, Mn(129-374 mg/kg)＞Zn(19-106 mg/kg)＞Cu(6-87 mg/kg)＞Cd(4.6-7.6 mg/kg)＞Pb(0.2-3.7 mg/kg), in BCF; Enteromorpha, Cd＞Mn＞Cu＞Zn＞Pb, Ilyoplax deschampsi, Cu＞Cd＞Mn＞Zn＞Pb, Urechis unicinctus, Cd＞Zn＞Mn＞Cu＞Pb. Some metal concentrations of Enteromorpha, especially Cu, Zn, weakly Pb in bukhang, Mn, Cd in boggili-ri, were correlate well with concentrations in sediment, indicating relatively more contaminated by the anthropogenic origin of metals in each tidal flat. The results clearly indicate that the seafood of bukhang, even of Boggili-ri known as clean area, are contaminated with metals.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.17-25
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• 2016

In this study, the air quality of underground and overground railway stations was evaluated focusing on the degree of influence of the outside air quality. The measured components were particulate matter ($PM_{10}$), carbon dioxide ($CO_2$), carbon monoxide (CO), nitrogen dioxide ($NO_2$), formaldehyde (HCHO), ozone ($O_3$), total airborne bacteria (TAB), total volatile organic carbon (TVOC), and Radon (Rn), which are included in the maintenance standards and recommended standards of the Indoor Air Quality Management Act. Also, the indoor/outdoor concentration ratios of $PM_{10}$, $NO_2$, and $O_3$ were calculated to estimate the influence of the outdoor air quality. The concentrations of $PM_{10}$ HCHO, TVOC, $NO_2$, and Rn in the underground stations were found to be higher than those in the overground stations. These results indicate that the (present) generation of contaminants are caused by the indoor source of the underground station. The ozone concentration of the overground stations was higher than that of the underground stations, which indicates that the outdoor ozone concentration influenced that of the overground stations directly. Thus, methods of improving the IAQ should take into consideration the types of contamination.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.64.2-64.2
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• 2019

It is known that lights scattered by comets and asteroids are partially polarized. From polarimetric observations of those objects, we can investigate physical properties, such as albedos, sizes of cometary dust particles and regolith of asteroids. Since the polarization degrees of those objects highly depend on their phase angles (Sun-object-observer's angles), long-term monitoring observations are required. Moreover, comets show unforeseeable activations (i.e., outbursts) which need follow-up observations to understand the mechanism. In order to realize such monitoring and transient observations, we installed the Triple-Range Imager and POLarimeter (TRIPOL) on the 61cm telescope of Seoul National University (Hereafter, SNU) Gwanak campus. With this combination, we can obtain g', r', i' bands photopolarimetric images simultaneously with $8.0^{\prime}{\times}8.0^{\prime}$ field of view and pixel resolution of 0.94" pixel-1. Here, we make a presentation regarding the photometric and polarimetric performances of TRIPOL on the SNU 61cm telescope. In addition, we introduce initial polarimetric results of asteroid and comets with the instruments. First, we determine the limiting magnitudes (defined as magnitudes for S/N=5) of $15.17{\pm}0.06$ (g'-band), $15.68{\pm}0.01$ (r'-band), $16.24{\pm}0.03$ (I'-band), respectively, with total 240-seconds exposure (four 60-seconds exposure images, each was taken at different rotation angle for the half-wave plate). Second, we found that the instrumental polarization is negligibly small, ($-0.32{\pm}0.04%$ in the g', $-0.36{\pm}0.05%$ in the r' and $-0.21{\pm}0.04%$ in the i'-bands), while the polarization efficiencies are large enough to maximize the performance (i.e., $97.52{\pm}0.03%$ in the g', $98.83{\pm}0.02%$ in the r' and $99.15{\pm}0.02%$ in the i'-bands). With the instruments, we made observations of three Jupiter-family comets, 21P/Giacobini-Zinner, 38P/Stephan-Oterma, and 46P/Wirtanen and plan to observe one near-Earth asteroid, (433) Eros, on a trial basis. Especially for comets, we discriminate signals from dust and gas to eliminate gas contamination, which are known to change observed degree of linear polarization, using multi-band images. We confirm that the phase angle dependency of these comets are consistent with previous observations, probably because polarimetric property of Jupiter-family comets are broadly homogeneous unlike asteroids. We will also describe future observation plans using TRIPOL and SNU 61cm telescope.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.33 no.2
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• pp.93-102
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• 2023

Objectives: With the evolution of direct reading sensors, it is possible to monitor several substances through telecommunication. However, there are some limitations on the use of direct reading technologies in the Occupational Safety and Health Act in South Korea, which only applies to detector tubes, noise, heat, and carbon monoxides. The number of chemicals and their amount of use have been continuously increasing in South Korea. The Ministry of Employment and Labor (MoEL) has concerns about worker's health because exposure is only covered for about 1.2% of all distributed chemicals. Using a direct reading monitor with photoionization detectors (PID-DRMs), gases and vapors chemicals can be measured. Based on the data, business owners are able to create corrective strategies, provide better working routines, and select correct respiratory equipment. PID-DRMs are less expensive and easier to handle for an owner voluntarily controlling chemicals emitted in the workplace. However, there are several limitations on using these PID-DRMs to the degree that the MoEL has not been able to select a legal monitor. The aim of this study was to review previous studies related to PID-DRMs and identify the characterization and limitation on PID-DRMs. Methods: To search for related studies on PID-DRMs, key words were used including direct reading monitors/instruments and/or photoionization detectors. Through that, four domestic and 15 international studies were reviewed. Results: Studies on PID-DRMs were conducted by chamber (enclosed, dynamic, walk-in) and in the field (experimental environment, actual environment). The concentration of PID-DRMs and charcoal tubes were compared for a single substance or mixture, or within the PID-DRMs. There was a high correlation between the two concentrations, but it did not meet the accuracy criteria (95% confidence interval, within 25%) of the NIOSH technical report (2012). In addition, differences in measured values occurred according to environmental factors (temperature, humidity) and high concentration, and concentration values tended to be underestimated due to contamination of the sensor. As a way to improve the accuracy of PID concentration, it was proposed to use correction factors, charcoal tube-based correction factors, or to calibrate the PID-DRMs in the same environment as the workplace. Conclusions: PID-DRMs can likely be used by business owners for the purpose of voluntarily managing the workplace environment, and it is expected that it will be possible to use them as legal equipment if a PID sensor can be upgraded and the limitations of the sensor (temperature, humidity, high concentration evaluation, sensor pollution) can be overcome in the near future.

• Economic and Environmental Geology
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• v.23 no.4
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• pp.425-452
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• 1990

A tentative hydrogeologic and hydrodispersive study was carried out to evaluate the groundwater pollution potential at a selected site by utilizing empirical assessment methodologies in an advanced stage of quantitative computer aided assessment. The upper most aquifer is defind as saturated overburden and weathered zone including the upper part of highly fractured rock. Representative hydraulic conductivity and storativity of the uppermost aquifer are estimated at 2.88 E-6 m/s and 0.09, respectively. Also calculated Darcian and average linear velocity of groundwater along the major pathway are 0.011 m/d and 0.12 m/d with average hydraulic gradient of 4.6% in the site. The results of empirical assessment methodologies indicate that 1) DRASTIC depicts that the site is situated on non-sensitive and non-vulnerable area. 2) Legrand numerical rating system shows that the probability of contamination and degree of acceptability are classed to "Maybe-Improbable, and Probable Acceptable and Marginally Unacceptable" with situation grade of "B". 3)Waste soil-site interaction matrix assessment categorizes that the study site is located on "Class-8 Site".

• Journal of the Korean Society of Food Science and Nutrition
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• v.31 no.2
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• pp.216-220
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• 2002

The microbiological examinations of food service operations were conducted for the hygienic evaluation at four elementary schools in Busan, Korea. Total one hundred and seventy two swabbed samples using sponge were collected from the surface of environments, utensils and equipments of food service facilities and analyzed by measuring the total, coliform and psychrotrophic count. Sampling sites were the surfaces of floors, drains, walls, knives, cutting boards, rubber gloves, vinyl aprons, plastic containers, carriers, shelves, trays, dry shelves, electric tray dryer, food containers, soup containers, rice cookers, frying pans, boiling cookers, refrigerators, dumb waiters and dishwashers. The swabbed samples kept in an ice-parked box were transported to a laboratory and analyzed. The results demonstrated that the degree of contamination depended on the sampling sites. Averages of total counts of surface swab samples were ranged from 0.62 to 7.79 Log CFU/200 cm$^2$. The level of coliforms were ranged from not detectable to 5.26 Log CFU/200 cm$^2$, and those of psychrotrophs from not detectable to 6.15 Log CFU/200 cm$^2$. The severely contaminated sites were dumb waiters, drains, rice cookers, knives, plastic containers and floors. Also cutting boards, rubber gloves, carriers, drying shelves, vinyl aprons, boiling cookers, soup containers, frying pans and refrigerators were highly contaminated with the level of abode 3.5 Log CFU/200 cm$^2$. Therefore, those sites should be focused and controlled according to control points of sanitation standard operating procedures (SSOP). Also, periodic microbiological examination in addition to visual examination is recommended on these highly contaminated sites indicated above results at food service operations in elementary school.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2000.05a
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• pp.59-63
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• 2000

At military bases, environmental restoration activities resulting from oil contamination are growing concerns of preventing adverse effects on human health and environments. Its technologies are still under developing stage through some countries such as United States and Germany. This study is focused on developing model for a decision-maker to assist the restoration priority under the situation of limited resources such as budget and time. The Model, named the Base Restoration Priority Decision model(BRP model), is composed of the three factors : oil contaminants receptors, and the potential migration pathways. Each risk rating of factor is combined in the 27 matrix blocks and set immediate, moderate, and delayed action category designated restoration priority. This is categorized to group sites into three degree using the simplest of assessment system. As a result, the model will be able to apply to the effective allocation of resources for the restoration by any decision-maker because the model is easy to understand. Also, the continuous study will have established risk assessment system for the restoration of contaminated military with this study as the starting point.