• Ocean Systems Engineering
• /
• v.12 no.1
• /
• pp.39-61
• /
• 2022

Renewable energy such as wave energy has gained popularity as a means of reducing greenhouse gases. However, the high cost and lack of available sea space in some countries have hindered the deployment of wave energy converters (WEC) as alternative means of sustainable energy production. By combining WECs with infrastructures such as floating breakwaters or piers, the idea of electricity generated from WECs will be more appealing. This paper considers the integration of vertical raft-type WEC (commonly known as the vertical flap WEC) with floating breakwater as means to generate electricity and attenuate wave force in the tropical sea. An array of 25 WECs attached to a floating breakwater is considered where their performance and effect on the wave climate are presented. The effects of varying dimensions of the WEC and mooring system of the floating breakwater have on the energy generation are investigated. The integrated WECs and floating breakwater is subjected to both the regular and irregular waves in the tropical sea to assess the performance of the system. The result shows that the integrated vertical flap-floating breakwater system can generate a substantial amount of wave energy and at the same time attenuate the wave force effectively for the tropical sea when optimal dimensions of the WECs are used.

• Transactions of the Korean hydrogen and new energy society
• /
• v.34 no.6
• /
• pp.722-727
• /
• 2023

There are various types of hydrogen production methods, but among them, the alkaline water electrolysis method produces hydrogen by electrolyzing water, and unlike other methods, it can produce green hydrogen that does not emit pollutants and greenhouse gases. There are many different potential risk factors inherent in the water electrolysis process. So it is necessary to predict an emergency situation in advance and to safely manage and take countermeasures according to the emergency situation. Korea Gas Safety Corporation (KGS) CODE AH271 stipulates legal matters to secure safety, but it is not detalied. Thus it is necessary to take measures to safely control and manage it according to the situation in which an emergency stop is required. In this study, based on KGS CODE and HAZOP for alkaline water electrolysis facilities, factors that can cause emergency situations were derived and countermeasures were prepared.

• Journal of ILASS-Korea
• /
• v.28 no.4
• /
• pp.176-183
• /
• 2023

Many countries are striving to reduce carbon emissions with the goal of net zero by 2050. Accordingly, vehicles are rapidly being electrified to reduce greenhouse gases in the transportation sector. However, many organizations predict that internal combustion engines of LDV (light-duty vehicle) will exist even in 2050, and it is difficult to electrify aircraft and large ships in a short time. Therefore, synthetic fuel (i.e., e-Fuel) that can reduce carbon emissions and replace existing fossil fuels is in the spotlight. The e-Fuel refers to a fuel synthesized by using carbon obtained through various carbon capture technologies and green hydrogen produced by eco-friendly renewable energy. The purpose of this study is to compare and analyze the injection and spray characteristics of the simulated e-Gasoline. We mixed the hydrocarbon fuel components according to the composition ratio of the synthetic fuel produced based on the FT(Fischer-Tropsch) process. As a result of injection rate measurement, simulated e-Gasoline showed no significant difference in injection delay and injection period compared to standard gasoline. However, due to the low vapor pressure of the simulated e-Gasoline, the spray tip penetration (STP) was lower, and the size of spray droplets was larger than that of traditional gasoline.

• Journal of Korean Society of Forest Science
• /
• v.96 no.3
• /
• pp.307-316
• /
• 2007

Yellow poplar (Liriodendron tulipifera L.) has low germination rate relatively other species, so the seedling production of Yellow poplar is a hard task. Accordingly this study was conducted to determine the optimal germination conditions for healthy seedling production and to promote survival rate after afforestation. Gemination percentage was examined at different media and seed covering materials using planting flats in the greenhouse. The best germination percentage was observed in sand for media and compound soil for covering materials. But it was time to transplant, seedlings became a poor character (i.e. height, root length, number of root, dry weight) in sand for media. In order to produce healthy seedlings, each different medium was compounded with TKS-2 (this is a gardening bed soil.) in the ratio 1:1 (v/v.), and compared two conditions. Quality of seedling was better than not mixed TKS-2 into each medium. Transplanting seedlings from greenhouse to nursery grew up rapidly 2 months later (early in August~early in October). Growth amount during two months corresponded to 85.6% and 71.3% in total growth amount of height and diameter at root collar, respectively. In the case of the competition-density effect on yellow-poplar seedlings, direct seedling produced the maximum 35 standard seedlings above 8 mm of root collar diameter per $m^2$, while transplanting seedling produced the maximum 64 standard seedlings per $m^2$. And produced seedlings of two way were significantly different rootlet while axial root and lateral root was not significantly different.

• Journal of Korean Society of Disaster and Security
• /
• v.16 no.4
• /
• pp.45-59
• /
• 2023

The global focus on mitigating climate change has traditionally centered on carbon dioxide, but recent attention has shifted towards methane as a crucial factor in climate change adaptation. Natural settings, particularly aquatic environments such as wetlands, reservoirs, and lakes, play a significant role as sources of greenhouse gases. The accumulation of organic contaminants on the lake and reservoir beds can lead to the microbial decomposition of sedimentary material, generating greenhouse gases, notably methane, under anaerobic conditions. The escalation of methane emissions in freshwater is attributed to the growing impact of non-point sources, alterations in water bodies for diverse purposes, and the introduction of structures such as river crossings that disrupt natural flow patterns. Furthermore, the effects of climate change, including rising water temperatures and ensuing hydrological and water quality challenges, contribute to an acceleration in methane emissions into the atmosphere. Methane emissions occur through various pathways, with ebullition fluxes-where methane bubbles are formed and released from bed sediments-recognized as a major mechanism. This study employs Biochemical Methane Potential (BMP) tests to analyze and quantify the factors influencing methane gas emissions. Methane production rates are measured under diverse conditions, including temperature, substrate type (glucose), shear velocity, and sediment properties. Additionally, numerical simulations are conducted to analyze the relationship between fluid shear stress on the sand bed and methane ebullition rates. The findings reveal that biochemical factors significantly influence methane production, whereas shear velocity primarily affects methane ebullition. Sediment properties are identified as influential factors impacting both methane production and ebullition. Overall, this study establishes empirical relationships between bubble dynamics, the Weber number, and methane emissions, presenting a formula to estimate methane ebullition flux. Future research, incorporating specific conditions such as water depth, effective shear stress beneath the sediment's tensile strength, and organic matter, is expected to contribute to the development of biogeochemical and hydro-environmental impact assessment methods suitable for in-situ applications.

• Journal of Bio-Environment Control
• /
• v.25 no.3
• /
• pp.212-217
• /
• 2016

This study was conducted to investigate the effect of nursery period on growth and yield attribute of green papaya (var. Red lady). The nursery period was 3, 5, 7, 9, 11 and 13 months and the green papaya was transplanted on 15 April, 2015 in a non-heated greenhouse. The plant height, node number and fresh weight of nursery plant were increased as the nursery periods increased. The growth of green papaya with 13 months nursery period was better than those of other treatments. First harvest after transplanting was increased as the nursery periods were shorten. It took 137 days (18 August) at 13 months treatment, and 184 days (2 October) at 3 months treatment. The fruit length and diameter were smallest at 3 months treatment and there was no significant difference among other treatments. The fruit yield was also influenced by the nursery periods, the commercial yield was also increased as the nursery periods increased. The commercial yield was highest at 13 months treatment (3,172kg/10a), followed by 11 (2,247kg/10a) and 9 months treatment (2,357kg/10a). At 7 and 5 months treatment were 1,942kg/10a and 1,787kg/10a, respectively and the yield was lowest at 3 months treatment (1,443kg/10a). The commercial yield was significantly decreased under 7 months treatment. Although the harvest time of 11 months treatment was earlier than that of other treatments in non-heated greenhouse, 9 month treatment will be more recommendable for green papaya production because of operating costs.

• Ocean and Polar Research
• /
• v.34 no.4
• /
• pp.365-384
• /
• 2012

Microalgae are photosynthetic microorganisms that are highly productive in the presence of basic renewable natural sources (light, $CO_2$, water and nutrients). They can synthesize lipids, carbohydrates and proteins in a small number of days. Subsequently, these carbon-captured products can be processed into both biofuels and valuable co-products. Additionally, microalgae would be an ideal feedstock for replacing land-based food crops with cellular products as high energy density transportation fuels. These microscopic organisms could contribute a significant amount of renewable energy on a global scale. In Korea, microalgae biofuel research was common in the early 1990s. The research activities were unfortunately stopped due to limited governmental funds and low petroleum prices. Interest in algal biofuels in Korea has been growing recently due to an increased concern over oil prices, energy security, greenhouse gas emissions, and the potential for other biofuel feedstock to compete for limited agricultural resources. The high productivity of microalgae suggests that much of the Korean transportation fuel requirements can be met by biofuels at a production cost competitive with the increasing cost of petroleum seen in early 2008. At this time, the development of microlalgal biomass production technology remains in its infancy. This study reviewed microalgae culture systems and biomass production, harvesting, oil extraction, conversion, and technoeconomical bottlenecks. Many technical and economic barriers to using microalgal biofuels need to be overcome before mass production of microalgal-derived fuel substitutes is possible. However, serious efforts to overcome these barriers could become a large-scale commercial reality. Overall, this study provides a brief overview of the past few decades of global microalgal research.

• Journal of Food Hygiene and Safety
• /
• v.33 no.1
• /
• pp.31-37
• /
• 2018

This study was conducted to evaluate the microbiological safety of leafy vegetables (perilla leaf and lettuce) in relation to cultivation methods. A total of 2,304 samples were collected from plants, harvesting tools and soil mulching film during the production and harvest stages from organic- and conventional- farms. From the samples, sanitary indicator microorganisms (total aerobic bacteria, coliforms, E. coli., Environmental Listeria, and yeast and mold) and pathogenic microorganisms (S. aureus, B. cereus, Salmonella spp., Clostridium spp., and L. monocytogenes) were analyzed. In the production stage of leafy vegetables, the sanitary indicator microorganisms was not detected regardless of cultivation method or it was detected to be less than $3.4\;Log\;CFU/100cm^2$. B. cereus and S. aureus were found to be 0.22~1.55 Log CFU/g in perilla leaf and lettuce produced by organic farms, and S. aureus was not detected and B. cereus was found to be 0.42~2.19 Log CFU/g in conventional farms. There were no significant differences between two cultivation methods. In the harvesting tools and soil mulching film, the contamination levels of sanitary indicator microorganisms and pathogenic microorganisms was low regardless of the cultivation method. However, there was a positive correlation ($R^2=0.4526$) in that the higher the microbial contamination level in the harvesting tool, the higher the microbial contamination on the surface of the plant. In addition, sanitary indicator microorganisms and pathogenic microorganisms were not detected or low in soil mulching during the production of organic leafy vegetables. As a result of this study, microbial hygiene control by soil mulching and harvesting tools was more important than difference of cultivation method in production of leafy vegetables.

• Journal of Korean Society of Environmental Engineers
• /
• v.34 no.11
• /
• pp.765-771
• /
• 2012

In this study, the biochemical methane potentials of different agricultural residues produced from agricultural plastic greenhouse were determined. Additionally, ensiling storage practice was applied on agricultural residues for its effect on biogas production. Agricultural residues of cabbage, strawberry, tomato, cucumber, and oriental melon were selected as sample. The methane potential and biodegradability of agricultural residues ranged from 149~286 mL-$CH_4/g$-VS, 27~48% (by vol.), respectively and methane production was in order of cabbage > oriental melon > strawberry ${\approx}$ cucumber > tomato. Ensiling caused difference in methane production in a range of -11~36% (by vol.) per VS compared with raw material. An increase in methane potential was presumably linked to the organic acid accumulation, cellulose degradation and decrease in methane potential was due to chemical composition change, ammonia accumulation during the storage process.

• Korean Journal of Ecology and Environment
• /
• v.34 no.4 s.96
• /
• pp.261-266
• /
• 2001

Effects of elevated carbon dioxide ($CO_2$) on soil microbial processes were studied in a northern peatland. Intact peat cores with surface vegetation were collected from a northern Welsh fen, and incubated either under elevated carbon dioxide (700 ppm) or ambient carbon dioxide (350 ppm) conditions for 4 months. Higher algal biomass was found under the elevated $CO_2$ condition, suggesting $CO_2$ fertilization effect on primary production, At the end of the incubation, trace gas production and consumption were analyzed using chemical inhibitors. For methane ($CH_4$ ), methyl fluoride ($CH_3F$) was applied to determine methane oxidation rates, while acetylene ($C_2H_2$) blocking method were applied to determine nitrification and denitrification rates. First, we have adopted those methods to optimize the reaction conditions for the wetland samples. Secondly, the methods were applied to the samples incubated under two levels of $CO_2$. The results exhibited that elevated carbon dioxide increased both methane production (210 vs. $100\;ng\;CH_4 g^{-1}\;hr^{-1}$) and oxidation (128 vs. $15\;ng\;CH_4 g^{-1}\;hr^{-1}$), resulting in no net increase in methane flux. For nitrous oxide ($N_2O$) , elevated carbon dioxide enhanced nitrous oxide emission probably from activation of nitrification process rather than denitrification rates. All of these changes seemed to be substantially influenced by higher oxygen diffusion from enhanced algal productivity under elevated $CO_2$.