• 대한토목학회논문집
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• 제29권1A호
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• pp.101-108
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• 2009

급속 포장 콘크리트는 타설 직후 공기 중에 노출되어 물리적, 화학적 영향을 많이 받아 유해물질들의 콘크리트 구조물 내부로 침투하여 사용연한이 감소하게 된다. 이와 같이 콘크리트 투과 특성은 내구성능을 결정하는데 중요한 요소이다. 또한 조강시멘트와 조강제의 성능으로 인하여 급격한 수화반응으로 인한 수화열로 열과 수분의 이동이 증가하여 구조물에 인장응력을 발생시켜 미소균열을 발생시킨다. 본 연구에서는 대단면 포장체의 급속 시공용으로 도출된 배합을 바탕으로 물투수시험, 동결융해반복시험, 마모저항성시험, 표면박리시험 및 소성수축, 건조수축, 자기수축 등의 시험을 실시하였다. 시험결과 조강제 및 섬유를 혼입한 배합이 가장 우수한 결과를 보여주었다.

• 한국양식학회지
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• 제15권1호
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• pp.49-60
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• 2002

Research on practices for improving water quality in channel catfish Ictalurus punctatus ponds was conducted at the Auburn University Fisheries Research Station, Auburn, Alabama, in 1998 and 1999. The objective of this two-year study was to determine better management practices to enhance water quality and improve production efficiency. In the first year, oxidation of bottom soil by drying, tilling, and applying sodium nitrate was performed (dry-till and dry-till with sodium nitrate treatments). The second year, based on the results obtained during the first year, precipitation of phosphorus (P) from water by applying gypsum was compared to the dry-till treatment (dry-till and dry-till with gypsum treatments). Control ponds were not subjected to bottom drying, tilling, sodium nitrate, or gypsum treatment. Channel catfish fingerings were stocked at 15,000/ha. In the first year, water in ponds from dry-till and dry-till with sodium nitrate treatments had lower concentrations (P < 0.01) of soluble reactive P, nitrate ($NO_{3} ^{-}) and nitrite ($NO_{2} ^{-}) nitrogen (N), total ammonia ($NH_3$) nitrogen, total suspended solids and turbidity, and higher values of pH, Secchi disk visibility, total alkalinity, total hardness, and calcium ($Ca^{2+}) hardness than water in control ponds. Ponds of the dry-till treatment also had lower concentrations (P < 0.01) of total P and total N than control ponds. Total fish production and survival rate did not differ among the treatments (P > 0.05). The findings suggested that drying and tiling pond bosoms between crops could achieve water quality improvement. Applying sodium nitrate to dry, tilled pond bosoms did not provide water quality improvement. In the second year, the treatment with the best results from the first year, dry-till, was compared with a dry-till with gypsum treatment. Enough gypsum was applied to give a total hardness of about 200 mg/L, and gypsum was reapplied as needed to maintain the hardness. Compared to the control, dry-till and dry-till with gypsum treatments had lower concentrations (P < 0.01) of total and soluble reactive P, total N, and total $NH_3$-N, and higher concentrations (P < 0.01) of dissolved oxygen. Ponds of the duty-till with gypsum treatment also had lower concentrations (P < 0.01) of chlorophyll $\alpha$, chemical oxygen demand, and total alkalinity than the control. Total fish production and survival rate did not differ (P > 0.05) among the treatments. These findings suggest that drying and tilling pond bosoms between crops and treating low hardness waters with gypsum could achieve water Quality improvement.

• 청정기술
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• 제29권2호
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• pp.95-101
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• 2023

폐굴껍질을 원료로 vaterite 형 침강성 탄산칼슘 제조 실험을 하였다. 굴껍질을 800℃의 온도에서 산화칼슘이 주성분인 소성 굴껍질을 제조하였다. 이 굴껍질을 질산이나 염산 용액에 녹여 0.1 M 질산칼슘이나 염화칼슘 수용액을 만들고, 여러 실험 조건에서 0.1 M 탄산나트륨 수용액과 탄산화 반응을 시켰다. 실험 조건은 aspatic acid 첨가량, 반응온도, 교반속도, NH₄OH 첨가량, 반응시간, 용해 산 종류 등이다. XRD, SEM, Size 분석을 하고 vaterite 함유량을 계산하였다. 25℃, 600 rpm, aspatic acid 0.1몰/ 1몰 CaO과 2 cm³의 NH₄OH를 첨가한 최적 조건에서 1시간 반응에서 vaterite 함유량 95.9%의 구형의 침강성 탄산칼슘을 합성하였다. 평균 입경은 12.11 ㎛이었다. 고 vaterite 함유 탄산칼슘은 의료용, 식용, 잉크첨가제 등 고부가가치 탄산칼슘으로 활용된다.

• 한국결정성장학회지
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• 제9권6호
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• pp.570-573
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• 1999

Ca nitrate와 인산을 혼합한 용액을 졸-겔법을 이용하여 Si(100) 기판 위에 스핀 코팅하여 열처리 함으로써 의치공 재료에 응용되는 하이드록시아파타이트 박막을 제조하였다. Si 기판 위에 아이드록시아파타이트막을 코팅하여 건조시킨 다음, $500^{\circ}C$에서 10분간 초벌구이 열처리를 하였다. X-선 회절 분석을 이용하여 $500^{\circ}C$에서 하이드록시아파타이트 상의 생성을 확인하였고, $500^{\circ}C$~$700^{\circ}C$ 및 $900^{\circ}C$에서 각각 tricalcium phosphate상의 생성을 확인하였다. FTIR(Fourier transform infrared spectroscopy)의 결과를 바탕으로 열처리 온도 증가에 따른 탄소량의 변화와 결정화도의 증가를 확인하려 한다.

• 한국대기환경학회지
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• 제13권6호
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• pp.439-450
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• 1997

Atmospheric fine particles $(PM_{2.5})$ were collected at the background sites, Kangwha, Taean, and Kosan and characterized to understand their behaviors at the sites. Daily samples of $PM_{2.5}$ mass were measured and ionic species, carbonaceous species, and gaseous species were analyzed. Four-day backward trajectory analysis was also carried out. The mean concentrations of anthropogenic species were highest at Kangwha among three sites, while contributions from sea salts wree highest at Taean during the measurement period due to higher wind speed at Taean. Major chemical components in fine particles were sulfate, organic carbon, nitrate, and ammoniu. Most of the non-sea-salt (nss) sulfates in $PM_{2.5}$ might be present as ammonium sulfates at these sites. Most air parcels arriving at Kangwha and Taean were from northern China. Therefore, both sites were thought to be affected by the same air parcel. At Kosan, during the measurement period, air parcels were from either northern China or sourthern China. The nss sulfate concentration in the air parcels from southern China was higher, while the nss calcium, nitrate, and ammonium concentrations were higher when the air parcels were from northern China.

• 한국지하수토양환경학회지:지하수토양환경
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• 제17권4호
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• pp.19-26
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• 2012

The influence of operation time on electrokinetic restoration was investigated to remove salts from sulfate-accumulated greenhouse soil. Operation time is directly related to the process cost, therefore, we determined the relationship between operation time and removal of salts. Nitrate and sodium were removed almost completely within 2 weeks, chloride and calcium was removed in proportion to the operation time. Sulfate was accumulated at the center of anode and cathode. The soil electrical conductivity (EC), an indicator for soil salinity, showed similar shape with the residual sulfate after electrokinetic treatment. The soil EC was not changed after 2 weeks, however, the energy consumption increased with operation time. Based on the experimental results, most salts except sulfate were removed within 2 weeks, but sulfate was not removed during same time period. For the further removal of sulfate, longer operation time is in need.

• Journal of Microbiology and Biotechnology
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• 제12권1호
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• pp.137-141
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• 2002

Anabaena variabilis ATCC 29413 grew in chromium (Cr) containing Chu-10 (basal) and nitrate-supplemented media, and the growth of the organism in $100{\mu}M$ chromium was found to be 50% of that in control medium. The growth in nitrate $({NO_3}^-)$ supplemented cultures was better as compared to cultures grown in basal medium. Free cells from basal and nitrate-supplemented media removed 5.2 and 7.4 nmol of chromium $mg^{-1}$protein in 8 h, respectively, from the medium containing $30{\mu}M$ chromium. The efficiency of chromium removal increased 7-fold in imidazole buffer (0.2 M, pH 7.0). A cell density equivalent to $100{\mu}g$ protein $ml^{-1}$ was found to be optimum for maximum Cr removal. Entrapment of cells in calcium-alginate beads did not affect the rate of Cr uptake by the cells. The efficiency of the laboratory-scale continuous flow bioreactor $(12.5{\times}2cm)$ loaded with alginate-immobilized cells (10 mg protein) and fed with $30{\mu}M$ chromium solution was compared at different flow rates. The efficiency of the bioreactor varied with flow rates. In terms of percent removal of Cr from influent, a flow rate of 0.1 ml $min^{-1}$ was found to be optimum for 6 h (54% Cr removal efficiency). Maximum amount of Cr (883 nmol) was removed by the cells in 3 h at a flow rate of 0.5 ml $min^{-1}$. The potential use of A. variabilis in removing Cr from industrial effluents is discussed.

• 한국산학기술학회논문지
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• 제21권10호
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• pp.386-392
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• 2020

3D 프린팅 콘크리트는 연속 적층 시 적층고가 높아짐에 따라 콘크리트의 자중이 증가되기 때문에 연속 적층성 확보를 위해 하단부 콘크리트가 적정 시간에 경화되어야 한다. 특히, 기온이 낮은 동절기의 경우 콘크리트의 경화속도가 늦어지게 되는데, 3D 프린팅 콘크리트 시공 중 하단부 콘크리트의 강도발현이 낮아 콘크리트의 자중을 버티지 못하게 되면 적층된 콘크리트가 무너지게 되는 문제가 발생된다. 이러한 문제점을 해결하기 위해서는 저온환경에서의 3D 프린팅 콘크리트의 초기강도를 증진이 필수적이다. 국내외 문헌에서는 Amine계, Nitrate계, Sodium계, Calcium계 등의 무기계 화학 첨가제를 사용하여 콘크리트의 초기강도를 증진시킨 사례가 보고되고 있다. 이에 본 연구에서는 Amine계, Nitrate계 및 Sodium계 조강형 첨가제 샘플 5종을 제작하여 그 성능을 평가하였고, 우수한 성능을 보인 샘플을 선별하여 이를 적용한 3D 프린팅 콘크리트의 초기강도 특성을 확인하였다. 그 결과 Nitrate계 첨가제 사용 시 10 ℃ 환경에서 기존 20 ℃ 환경의 3D 프린팅 콘크리트 배합대비 동등 이상의 초기강도 발현이 가능한 것을 확인할 수 있었다.

• 한국습지학회지
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• 제7권4호
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• pp.33-42
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• 2005

Wetlands often function as a nutrient sink. It is well known that increased input of nutrient increases the primary productivity but it is not well understood what is the fate of produced biomass in wetland ecosystem. Water and sediment quality, decomposition rate of cellulose, and sediment accumulation rate in 11 montane marshes in northern Sierra Nevada, California were analyzed to trace the effect of nitrogen and phosphorus content in water on nutrient dynamics. Concentrations of ammonium, nitrate, soluble reactive phosphorus (SRP) in water were in the range of 27 to 607, 8 to 73, and 6 to 109 ppb, respectively. Concentrations of ammonium, calcium, magnesium, sodium, and potassium in water were the highest in Markleeville, which has been impacted by animal farming. Nitrate and SRP concentrations in water were the highest in Snow Creek, which has been impacted by human residence and a golf course. Cellulose decomposition rates ranged from 4 to 75 % per 90 days and the highest values were measured in Snow Creek. Concentrations of total carbon, nitrogen, and phosphorus in sediment ranged from 8.0 to 42.8, 0.5 to 3.0, and 0.076 to 0.162 %, respectively. Accumulation rates of carbon, nitrogen, and phosphorus fluctuated between 32.7 to 97.1, 2.4 to 9.0, and 0.08 to $1.14gm^{-2}yr{-1}$, respectively. Accumulation rates of carbon and nitrogen were highest in Markleeville and that of phosphorus was highest in Lake Van Norden. Correlation analysis showed that decay rate is correlated with ammonium, nitrate, and SRP in water. There was no correlation between element content in sediment and water quality. Nitrogen accumulation rate was correlated with ammonium in water. These results showed that element accumulation rates in montane wetland ecosystems are determined by decomposition rate rather than nutrient input. This study stresses a need for eco-physiological researches on the response of microbial community to increased nutrient input and environmental change because the microbial community is responsible for the decomposition process.

• 한국토양비료학회지
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• 제34권2호
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• pp.122-128
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• 2001

질소비종이 토양 pH. EC, $NO{_3}^-$ 함량 및 상추 생육에 미치는 영향을 조사하고자 양분함량이 서로 다른 두 토양을 사각폿트에 충진하여 유리온실 내에서 상추를 재배하였다. 상추재배를 위해, 7종류의 질소 비료(요소, 질산가리, 질산석회, 질산암모늄, 황산암모늄, 복비A(11-10-10), 복비B(12-12-12)를 토양검정 시비량으로 시용하였다. 토양 pH는 질산가리 및 질산칼슘 시용구를 제외한 비료시용구에서 시험전 토양보다 시험후 토양에서 낮아 졌는데, 질소비료중 황산암모늄 시용구에서 가장 낮았다. 토양 EC및 $NO_3-N$은 모든 비료 시용구의 시험후 토양에서 시험전 토양에 비해 높은 경향이었다. 상추의 생존율은 토양 EC가 $0.20dS\;m^{-1}$의 비료 시용구에서는 90% 이상이었으나, 토양 EC가 $1.13dS\;m^{-1}$에서는 감소되었다. 특히, 복비와 황산암모늄 시용구의 생존율은 각각 56%, 58% 정도로 감소되었다. 상추의 생산량은 토양 EC가 $0.20dS\;m^{-1}$에서는 비료 시용구에서 무비료구 보다 높았으나, 토양 EC가 $1.13dS\;m^{-1}$에서는 모든 질소 비료 시용구에서 무비료구 보다 낮았다. 상추 엽내 $NO{_3}^-$ 함량은 모든 비료 시용구에서 약 $1,000{\sim}2,000mg\;kg^{-1}$ FW 정도였다.