• 한국환경보건학회지
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• 제43권6호
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• pp.525-531
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• 2017

Objectives: The purpose of this experiment is to better understand the nitrogen and phosphorus removal ratio according to operating conditions in an iron electrolysis system consisting of an anoxic basin, aerobic basin, and iron precipitation apparatus. Methods: Iron electrolysis consists of an iron precipitation reactor composed of iron plates in oxic and anoxic basins. We studied the interrelation coefficient between T-N and T-P removal rates and F/M ratio, and the C/N ratio and BOD removal rate. Results: The F/M ratio and the T-N and T-P removal rate per unit area have interrelation coefficients of 0.362 and 0.603, respectively. The removal rate per MLVSS and the T-N and T-P removal rate per unit area have respective interrelation coefficients of 0.49 and 0.59. Conclusions: The removal rate of T-N and T-P increased with the increasing F/M ratio in the influent, and they also linearly increased in proportion to the C/N ratio of influent and BOD removal rate of the reactor.

• 한국환경과학회지
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• 제29권5호
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• pp.531-539
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• 2020

To understand the composition, quantity, and quality of Suspended Particulate Organic Matter (SPOM) in the Gangneung Namdae Stream, Korea, we examined spatiotemporal variations in water temperature, salinity, chlorophlly a (Chl a), Particulate Organic Carbon (POC) and nitrogen (PON), and carbon stable isotope (δ¹³C) of SPOM at six stations in June (pre-monsoon), July (monsoon), and September (post-monsoon) 2017. With increasing precipitation, the average POC and C/N values increased significantly in July than in June. In September, the values decreased with decreasing precipitation. The δ¹³C values showed irregular spatiotemporal fluctuations among the stations and periods, thereby suggesting a greater contribution of autochthonous organic matter to the pool of SPOM than that of allochthonous organic matter derived from upstream. In addition, the large and irregular changes in POC, C/N ratio, C:Chl a, and δ¹³C compared to that of PON were observed for all periods among the stations, indicating a serial discontinuity of the stream. Our results suggest that the Gangneung Namdae Stream is significantly influenced by the increase in freshwater discharge caused by heavy rainfalls during the summer monsoon and post-monsoon periods.

• 열처리공학회지
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• 제19권1호
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• pp.3-9
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• 2006

The phase changes, nitride precipitation and hardness variations of 14%Cr-6.7Ni-0.65Mo-0.26Nb-0.05V-0.03C super martensitic stainless steel were investigated after nitrogen permeation heat treatment at a temperature range between $1050^{\circ}C$ and $1150^{\circ}C$. The nitrogen-permeated surface layer was transformed into austenite. The rectangular type NbN, NbCrN precipitates and fine round type precipitate were coexisted in the surface austenite layer, while the interior region that was free from nitrogen permeation kept the martensitic phase. The hardness of surface austenite showed 280 Hv, while the interior region of martensite phase represented 340 Hv. When tempering the nitrogen-permeated steel at $450^{\circ}C$, a maximum hardness of 433 Hv was appeared, probably this is attributed to the secondary hardening effect of the precipitates. The nitrogen concentration decreased gradually with increasing depth below the surface after showing a maximum of 0.3% at the outmost surface. The strong affinity between nitrogen and Cr enabled the substitutional element Cr to move from interiors to the surface when nitrogen diffuse form surface to the interior. Corrosion resistance of nitrogen permeated steel was superior to that of solution-anneaed steel in the solution of 1N $H_2SO_4$.

• 열처리공학회지
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• 제20권2호
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• pp.84-93
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• 2007

Microstructural changes during tempering at the temperature range of $300^{\circ}C{\sim}700^{\circ}C$ for the nitrogen-permeated STS 410 and 410L martensitic stainless steels has been investigated. After nitrogen permeation at temperature between 1050 and $1150^{\circ}C$, the surface layer appeared fine $Cr_2N$ of square and rod types in the martensite matrices. Hardness of the nitrogen-permeated surface layer represented 680Hv and 625Hv, respectively, for 410 and 410L steels. It is considered that the fine homogeneously dispersive effect of precipitates by nitrogen caused the increased hardness. Due to the counter current effect of carbon from interior to surface during nitrogen diffusion from surface to interior, the 0.1%C alloyed 410 steel showed the low nitrogen content of 0.025% compared with 0.045% of 410L steel at the distance of $100{\mu}m$ from the surface. Tempering of nitrogen-alloyed 410 and 410L showed the maximum hardness at $450^{\circ}C$. This maximum hardness was considered to be the secondary hardening effect of very fine carbide and nitride. The decrease in hardness at $700^{\circ}C$ was the softening effect of the matrix due to the precipitation of many needle-shaped $Cr_2N$ for 410 steel and the precipitation of coarse nitride of $Cr_2N$ in line with the spherical precipitates with directionality for 410L steel. For 410 steel, the corrosion resistance of nitrogen permeated surface in the solution of 1 N $H_2SO_4$ were nearly unchanged, however the superior corrosion resistance was obtained for nitrogen permeated 410L steel compared to the solution annealed condition.

• 한국축산시설환경학회지
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• 제3권2호
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• pp.125-131
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• 1997

This paper was discussed N-balance of the republic of Korea. About 397Kg N/ha was inputted into the chemical fertilizer, animal feed, precipitation and nitrogen fixation. About 15kg N/ha was outputted from the Korea. The amount of N surplus was 397kg N/ha and loaded into environment. This causes the problem of water, air and soil pollution. It should take measures to improve the situation, such as depending more on selfsufficient feed and using nutrient cycling functions of soils.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1999년도 Proceedings of the 1999 Annual Conference The Korean Society of Agricutural Engineers
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• pp.739-746
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• 1999

Discharge characteristics of organic materials and nutrients were estimated in the catchment area of relaimed area-Saemankeum-. Discharge load of BOD5 was high in the domestic system, while nitrogen and phosphorous were discharged mainly from the livestock system and the land . Load was so dependent on the precipitation that it increased in the rainy season, particulary in nitrogen and phosphorus. Loads from nonpoint sources in this area were higher compared with others.

• 한국물환경학회지
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• 제22권1호
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• pp.51-58
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• 2006

The effluent limitations for individual industry based on the best available technology economically achievable (BAT) have been required to achieve effective regulation. BAT assessment criteria that are suitable for the circumstances of Korean industry were developed in the previous study. The criteria were applied to determine the BAT for leather tanning and finishing industry. For the evaluation BAT, a subcategorization for the industry considering wastewater characteristics, source equipments, raw material and so on should be suggested. Three subcategories: A) Unharing, Chrome Tan, Retan-Wet Finish, B) Chrome Tan, Retan-Wet Finish, and C) Furskins were proposed in this study. Wastewater discharged from the each category contains high concentration of COD, chrome, nitrogen and sulfide. In particular, the concentration of nitrogen from the subcategory A is significantly greater. Twenty sites were surveyed and wastewater qualities were analyzed. Therefore, six different technologies were applied to the subcategory A for the end-of-pipe treatment technology, and a technology was used in the subcategory B and C, respectively. The technology candidates were evaluated in terms of environmental impacts, economically achievability, treatment performance and economical reasonability. As the result, the technology options for each subcategories: A) primary chemical precipitation + modified Ludzack-Ettinger process (MLE) + secondary chemical precipitation, B) chemical precipitation + typical activated-sludge process + Fenton oxidation, C) chemical precipitation + typical activated-sludge process + batch Fenton oxidation or batch activated carbon treatment were selected as the BAT, respectively.

• Journal of Welding and Joining
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• 제20권5호
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• pp.63-71
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• 2002

One of the shortcoming of ferritic stainless steels is their limited toughness. The most important factor governing the toughness of ferritic stainless steels is hewn to be their interstitial contents. Due to the limited solubility of carbon and nitrogen in the ferrite matrix, it is difficult to avoid carbide and nitride precipitates. In the study, the role of nitrogen on the toughness of 260r-2Mo superferritic stainless steel welds has been investigated using alloys containing various nitrogen levels between 100 and 1640 ppm. Mechanical properties of weld metals have been evaluated by microhardness, Charpy impact test and notch tensile test. The alloys are mainly embrittled by the grain boundary and intragranular nitride precipitation. Grain boundary precipitates are considered to be more deleterious than intrauanular nitrides. Fracture mechanism have been elucidated through microscopic evaluation of notch tensile test

• Journal of Welding and Joining
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• 제16권3호
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• pp.121-128
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• 1998

The degradation of mechanical properties in the high nitrogen steel HN3 developed for nuclear fusion reactor has been evaluated quantitatively using the small punch(SP) test, X-ray diffraction (XRD) analysis has also been conducted to identify carbides or nitrides precipitated on grain boundaries of the heat treated samples. Mechanical properties of the steel HN3 significantly decreased with increasing heat treatment time and temperature or with decreasing testing temperature. Combination of XRD and metallurgical observation, revealed that the material degradation in the thermally aged steel was caused by precipitation of carbides on the grain boundaries. While the weld metal showed the lowest mechanical properties among various microstructures in GTA weldments. By combining SP test and XRD analysis, cryogenic fracture behaviors and aging degradation for high nitrogen steel could be successfully evaluated in nondestructive manner.

• 한국세라믹학회지
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• 제53권1호
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• pp.1-6
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• 2016

In this year, Koreans have a shortage in agricultural and drinking water due to severe algal blooms generated in major lakes. Waste oyster shells were obtained from temporary storage near the workplace at which oysters were separated from their shells. Heating ($1000^{\circ}C$ for 1 h in air) was employed to convert raw oyster shell powders into calcium oxide powders that reacted efficiently with phosphorus and nitrogen to remove algal blooms from eutrophicated wastewater. As the dispersed amount of heated oyster shell powders was increased, water clarity and visual light penetration were improved. Coagulation, precipitation and carbonation process of the heated oyster shell powders in a water purifier facilitated removal of eutrophication nutrient such as phosphorus and nitrogen, which is both beneficial and economically viable. $CO_2$ implantation by carbonation treatment not only produced thermodynamically stable CaO in oyster shells to derive precipitated calcium carbonate (PCC) but also accelerated algal removal by activation of coagulation and precipitation process. The use of oyster shell powders led to a mean reduction of 97% in total phosphate (T-P), a mean reduction of 91% in total nitrogen (T-N) and a maximum reduction of 51% in chemical oxygen demand (COD), compared with the total pollutant load of raw algal solution. Remarkable water quality improvement of algal removal by heated oyster shell powders and PCC carbonation treatment will allow utilization as water resources to agricultural or industrial use.