김태욱 Tae Wook Kim , 홍성철 Sungchul Hong , 이병인 Pyongin Yi , 장성호 Seongho Jang , 서정민 Jeongmin Suh , S. Sivakumar , 박제성 Jesung Park , 김기범 Gibeom Kim , 김준필 Jun Pil Kim , 정은상 Eunsang Jung

DOI:10.9786/kswm.2023.40.5.429

Abstract

The agricultural sector faces numerous challenges, including extreme climate change, rural aging, decreasing labor force and farmland, and rising labor costs. In response, the Korean government has introduced policies to support young farmers. One noteworthy solution for enhancing crop production and optimizing farm management while reducing labor needs is hydroponic cultivation (or smart farming). In hydroponic greenhouses, rock wool is crucial in ensuring high crop yield and superior product quality. Globally recognized for its outstanding physical properties, rock wool excels in water retention. Yet, in Korea, recycling restrictions on post-harvest waste rock wool deter many from choosing it over other solid media. According to domestic regulations, rock wool is classified as general waste, prohibiting its direct landfilling or recycling. As a result, the agricultural usage of rock wool in Korea is limited due to the recycling restrictions, especially when compared to organic media. This research set out to investigate and comprehend the application of rock wool in facility-based horticultural farming, referencing both Korean practices and those abroad. The study explored the treatment of waste rock wool in foreign agricultural sectors. Furthermore, this research proposes feasible methods for processing waste rock wool and potential recycling strategies.

Key Words

Rock wool, Recycling method, Hydroponics, Smart farm, Greenhouse

주정호 Chenghao Zhu , 윤석표 Seok-pyo Yoon

DOI:10.9786/kswm.2023.40.5.441

Abstract

This study aims to identify the optimal conditions for the wet recycling of Manganese (Mn) found in the cathode active material of waste mobile chargers. The best condition to extract the cathode active material using acid was a mix of 2 M sulfuric acid and 2% H₂O₂, L/S = 20, over an extraction duration of 2 h, resulting in an equilibrium pH of 2.56 for the extract. The ideal conditions for the liquid/liquid separation with D2EHPA to isolate Mn from the acid extract were A : O = 1 : 1, an extraction period of 15 min, and an initial pH of 2.5 (equilibrium pH 3.5). Following the acid extraction of the cathode active material using sulfuric acid, an organic solvent was introduced, forming a MnSO₄-type precipitate, with Mn being recovered at close to 100%. The separation efficiency remained consistent, even when the organic solvent was reused twice.

Key Words

Waste mobile chargers, Manganese recovery, Sulfuric acid, D2EHPA

이현재 Hyunjae Lee , 양승민 Seungmin Yang , 강석구 Seoggoo Kang

DOI:10.9786/kswm.2023.40.5.451

Abstract

This study investigates a Torrefied wood flour mixed coagulant prepared by mixing torrefied wood flour with a strong negative charge and a cationic polyacrylamide. The effectiveness of the prepared coagulant in improving muddy water quality was verified by comparing turbidity, pH, dissolved solids content, total phosphorus (T-P), and total nitrogen (TN) removal rates for different coagulant types and injection amounts. Due to the water quality characteristics of each water treatment agent, the torrefied wood powder mixed coagulant led to a marginal PH reduction. Conversely, PAC showed a large pH drop, a decrease in turbidity improvement effect, and an increase in dissolved solids around pH 4.3. In terms of turbidity improvement effect, the torrefied wood powder mixed coagulant showed the best performance. However, with PAC, the turbidity improvement effect varied depending on the input amount and was about 13% compared to the maximum turbidity improvement effect under the 0.75 mL/L input condition. The torrefied wood powder mixed coagulant showed no substantial difference in turbidity improvement effect with varying input amounts and achieved a turbidity improvement effect and sedimentation rate about 10 times faster than PAC. Similar to the turbidity improvement effect, the T-N and T-P removal performance of PAC decreased rapidly compared to the 0.1 mL/L input condition under the input conditions between 0.25 mL/L and 1 mL/L. For an input amount of 0.75 mL/L or less, the torrefied wood powder mixed coagulant had better T-N removal efficiency. In the case of T-P, the torrefied wood powder mixed coagulant showed a higher removal rate than PAC at an input amount of 0.5-0.75 mL/L, with a removal rate of 65-85% compared to the PAC input in other ranges.

Key Words

Muddy water, Torrefied wood flour, Coagulant, Turbidity

방건웅 Gunwoong Bahng , 서명희 Myung Hee Suh , 홍한의 Han Eui Hong

DOI:10.9786/kswm.2023.40.5.461

Abstract

A novel method was developed to convert oyster shells into powder using microorganisms, offering an innovative approach to recycling. The primary constituents of these microorganisms were Firmicutes, Bacteroidota, and Actinobacteriota. When combined with these microorganisms, fresh oyster shells transformed into powder within three days at 80oC. The resulting powder contained over 95% calcium carbonate. Its alkalinity was measured at 50.3%, and its salt content was under 2%. This powder holds potential as an organic fertilizer, desulfurizer, and gypsum board, etc. replacing limestone. Notably, this microbial method bypasses the need for high-temperature calcination, typically exceeding 700oC, resulting in considerably lower production costs than the conventional pyro-process. Fresh oyster shells can be processed directly at the production site, eliminating the need for extended drying times of over a year. This immediate treatment can prevent environmental issues, such as odors and leachate, from vast oyster shell waste yards. Furthermore, this process avoids carbon dioxide emissions from high-temperature decomposition.

Key Words

Oyster shell, Oyster shell powder, Microorganism, Calcination, Fertilizer

이현재 Hyunjae Lee , 양승민 Seungmin Yang , 강석구 Seoggoo Kang

DOI:10.9786/kswm.2023.40.5.471

Abstract

The study explores the potential of torrefied wood powder combined with fatty acids as an alternative ignition material for molded charcoal. The viability of this alternative was confirmed by evaluating its fuel properties, including the combustion rate, fixed carbon content, calorific value, ignition time, and combustion rates. The optimal torrefaction conditions for the wood flour were identified as a 20-minute treatment at 350℃, leading to the best fuel performance and the increased fixed carbon content from 10% to roughly 19%. Although torrefied wood powder has a lower fixed carbon and calorific value than charcoal, it has superior ignition capabilities and a higher combustion rate. When the charcoal-to-torrefied wood powder ratio reaches 7:3, the calorific value exceeds 6400 Cal/g, with a fixed carbon content of 65%. This also allows for a reduction in ignition time by approximately 12 seconds. Notably, the ignition efficiency of the torrefied wood powder is considerably enhanced when combined with fatty acids. The most significant improvement in ignition performance is observed when the fatty acid is melted and blended with the torrefied wood powder. Furthermore, when the standard barium nitrate and sodium nitrate mixture is substituted with torrefied wood powder combined with molten fatty acid, there is a notable increase in the fixed carbon content. This results in a rapid decrease in ash content, thereby improving the fuel's properties. The ignition time reduces significantly from 17 to 9 seconds, showcasing its potential as a novel ignition material substitute.

Key Words

Torrefied wood, Barium nitrate, Molded charcoal, Ignition, Fatty acid

김종범 Jong Bum Kim , 류재용 Jae Yong Ryu

DOI:10.9786/kswm.2023.40.5.481

Abstract

Sulfur hexafluoride (SF₆) is a greenhouse gas with a high Global warming potential, mainly utilized in the insulation of materials and semiconductors for electric power and transmission facilities in heavy electric fields. SF₆ gas is discarded after being used as an insulator for heavy electric devices. This study aims to find the major decomposition pathways of high-concentration SF₆ depending on water vapor in plasma technology. When the water vapor equivalent (1 : 3) was added, the main decomposition pathways of SF₆ gas were SO₂ and HF, with a small amount of SO₂F₂ generated. Upon addition of excess water vapor (1 : 6), the main decomposition pathways of SF6 gas were found to be SO₂ and HF. In the absence of water vapor, the main decomposition pathways of SF₆ gas were SO₂F₂ and F₂, with a small amount also decomposed into SO₂.

Key Words

Sulfur hexafluoride (SF₆) destruction pathway, Plasma, SO₂F₂, HF, Conditioning agent, Water vapor

엄용석 Yong-seok Eom , 백건욱 Geon-uk Baek , 김정현 Jung-hyeon Kim , 성진호 Jin-ho Sung

DOI:10.9786/kswm.2023.40.5.491

Abstract

This study aims to develop a cost-effective regeneration technology for diesel particulate filter (DPF) used to remove particulate matter (PM) emitted from diesel engines of island power plants, as existing regeneration technologies (thermal and chemical methods) have problems (cost and wastewater) due to the characteristics of the island areas. Therefore, the impulse of dry ice spray technology, which can be applied in the field by spray condition was compared and evaluated. Damage to the surface or pores of a DPF during the cleaning process can decrease the PM removal efficiency. Therefore, deriving appropriate regeneration conditions is necessary. An impulse of dry ice spray should not exceed an impulse resistance of 258 gf, as analyzed. The optimal dry ice spray condition was 6 bar of injection pressure, 50 mm of spray distance, 0.5 mm of dry ice diameter, and 1 kg/min of injection rate. When dry ice was sprayed on the discharged DPF after driving at the island power plant for 2,000 hr, the back pressure was regenerated from 100 to 6.6 mbar. CT imaging of regenerated DPF confirmed that only pollutants were removed without internal damage. Additionally, dry ice regeneration technology was the fastest, taking only 60 seconds compared to back-blowing and heat regeneration. The results of this study confirm the efficiency and cost-effectiveness of waste DPF regeneration technology using dry ice to other technologies.

Key Words

Dry ice, Spray, Impulse, Diesel particulate Filter, Regeneration

이정현 Jeong-hyun Lee , 이재영 Jai-young Lee

DOI:10.9786/kswm.2023.40.5.502

Abstract

This study aims to devise an evaluation indicator for the cleanliness of City A. This evaluation indicator seeks to enhance administrative processes and pinpoint cleaning services needing improvement. Currently, the evaluation criteria adopt the same measures across all districts, leading to potential result inaccuracies. To refine these criteria, officials from City A and environmental experts reviewed the cleaning and sanitation categories. Subsequently, these criteria were organized for a pairwise-comparison survey. Survey feedback was then assessed using the Analytic Hierarchy Process (AHP), factoring in the weight of each element. The AHP analysis revealed that waste collection was the most influential factor, with a significance of 0.40 in the cleaning services category. Moreover, the “finishing work” had the predominant importance with a weight of 0.27. With the insights from the AHP, City A can set policy agendas to ameliorate conditions post-waste collection. It is recommended to incorporate evaluation components from City A, which carry distinct weights as determined by varied respondent groups.

Key Words

Urban cleanliness, Analytic hierarchy process, Cleanliness indicators, Cleanliness services, Citizen satisfaction

윤상일 Sangil Yun , 송상훈 Sang-hoon Song , 이남훈 Nam-hoon Lee , 정민정 Min-jung Jung , 박진규 Jin-kyu Park

DOI:10.9786/kswm.2023.40.5.523

Abstract

The aerobic landfill method is the only known way to reduce greenhouse gas emissions and shorten the aftercare period of closed waste landfills, as demonstrated by various field cases abroad. The increasing problem of anaerobic landfills necessitates the exploration of new landfill management solutions. The success of aerobic landfill projects overseas suggests that aeration may be a viable approach for implementation in Korea but aerobic landfill methods have not been utilized in Korea to date. Therefore, this study aims to review global trends in aerobic landfill technologies, as one of the sustainable landfill methods, and assess their applicability in enhancing landfill stabilization and reducing greenhouse gas emissions in Korea. Our study reveals that aerating old landfills could efficiently reduce aftercare costs by 0.8% to 114%. The uncertainties surrounding nitrous oxide emissions and the operational lifespan of the aerobic landfill method persist. Additionally, Korea lacks institutional support for recognizing the greenhouse gas reductions achieved through the aerobic landfill method. However, considering current costs and savings, including installation and operation expenses of the aerobic landfill method, social costs of carbon, and future savings due to a shortened aftercare period, reduced aftercare costs through early stabilization, and increased land use value, the aerobic landfill method emerges as a landfill management technology that can substantially enhance the sustainability of Korea’s waste management practices.

Key Words

Sustainability, Waste management, Greenhouse gas, Aerobic landfill, Aftercare

채광석 Kwang-seok Chea , 구남인 Namin Koo , 천정화 Junghwa Chun , 양희문 Hee Moon Yang , 박기형 Ki-hyung Park

DOI:10.9786/kswm.2023.40.5.534

Abstract

This study investigated natural aggregates (forest, land, marine, and river) commonly employed as building materials over 29 years from 1992 to 2021. The research delved into extraction volumes and share of natural aggregates, focusing on forest aggregates, which are abundant and of excellent quality. Environmental pollution problems arising from the extraction of river aggregates were also investigated. In Korea, the extraction percentages based on natural aggregates (100%) in 2021 were as follows: forest aggregates accounted for 79.2%, marine aggregates for 14.69%, land aggregates for 5.5%, and river aggregates for 0.6%. Forest aggregates are increasing due to their abundance and excellent quality, while sea aggregates are being reduced to less than 5% due to conservation policies. Land and river aggregates are also decreasing due to ecosystem conservation and depletion. As natural aggregate collection shifts towards forest aggregate, we propose an effective approach for their collection.

Key Words

Forest aggregate, Marine aggregate, Land aggregate, River aggregate