이송현 Songhyun Lee , 김병환 Byeonghwan Kim , 지승민 Seungmin Ji , 장용철 Yong-chul Jang , 이어진 Eojin Lee , 박미솔 Misol Park , 김선용 Sunyong Kim , 심유나 Yuna Sim , 김동현 Donghyeon Kim , 한소영 Soyeong Han

DOI:10.9786/kswm.2021.38.4.281

Abstract

This study examined the current management and problems of discarded single-use masks in Korea during COVID- 19. Field visits have been made to identify potential problems associated with the disposal of single-use face masks. We analyzed a total of 32 discarded single-use face masks and newly made singe-use face masks for material composition and characteristics. Based on this study, there were more than 6.7 billion single-use masks manufactured in 2020, indicating that more than six times higher than the production of the masks in 2019 due to COVID-19 pandemic. The average use of single-use face masks per person was found to be 130 masks/yr, which is equivalent to 6.7 billion masks/yr in 2020 in Korea. After the collection of the used masks, the large fraction of discarded masks was incinerated (14,961 ton or 3.8 billion masks) and landfilled (8,056 ton or 2.1 billion masks). Only approximately 1% of the discarded masks from households was improperly disposed on streets, parks, roads, shopping carts, rivers and streams, and other environment. Improper disposal of such masks may pose a threat to humans, animals, and other ecological receptors because of potential spread of virus, the occurrence of microplastics and their non-biodegradable characteristics. Technical development of biodegradable face masks has been made from scientific community to reduce plastic pollution from single-use face masks. However, more research is still needed to warrant the safety, biodegradability, waste management, and economic factors of the eco-friendly face masks. Waste minimization and prevention of single-use face masks is a challenging task due to the preference of the mask to consumers over the COVID-19 pandemic.

Key Words

Single-use face masks, Disposal face mask, COVID-19, Recycling, Waste management

임진홍 Jin Hong Im , 장용철 Yong-chul Jang

DOI:10.9786/kswm.2021.38.4.294

Abstract

Plastic wastes are majorly packaging plastic materials composed of polyethylene terephthalate (PET). The improper disposal of PET bottles can cause severe environmental problems, such as environmental plastic pollution, greenhouse gas emission, resource depletion, and marine plastic pollution. Owing to the steady increase in the consumption of PET bottles, it is important to improve the recycling rates and quality of recycled PET products. This study analyzed the material flow of PET bottles in Korea in 2018 to develop an appropriate management policy for recycling PET bottles. In addition, the content of greenhouse gases reduced via the recycling of PET bottles was quantified using US EPA waste reduction model (WARM). The results revealed that approximately 301,000 tons of PET bottles were sold and discharged as plastic waste in 2018. In addition, approximately 236,000 tons of waste PET bottles were recycled. Consequently, about 240,000 tons of CO₂eq was reduced in 2018 and 1,768 thousand tons of CO₂eq was reduced from 2010 to 2018. This study aimed to highlight the potential benefits of recycling PET bottles by providing the content of reduced greenhouse gas and recycled materials. The quantitative analysis of the material flow revealed that it is essential to perform high-quality recycling of PET bottles (e.g., bottle-to-bottle and long-fiber uses) in contrast to low-grade recycling to achieve a circular economy.

Key Words

PET Recycling, MFA, GHG reduction, WARM, Circular economy

송상훈 Sang-hoon Song , 고준혁 Jun-hyeok Ko , 박상흠 Sang-heum Park , 김란희 Ran-hui Kim , 김상민 Sang-min Kim , 이남훈 Nam-hoon Lee , 박진규 Jin-kyu Park

DOI:10.9786/kswm.2021.38.4.303

Abstract

This study aims to analyze greenhouse gas (GHG) emissions reductions in anerobic municipal solid waste (MSW) landfills to evaluate the efficiency of active aeration in the reduction of GHG and to verify the accuracy of the methane correction factor (MCF) reported in the 2019 Refinement (i.e., 0.4). Experimental results revealed that the GHG reduction efficiency was 61.1%, which is slightly lower than that reported in literature. However, under the assumption that active aeration was applied to all MSW landfills in Korea in 2018, this finding indicates that active aeration reduced GHG emissions by 4.7 million tons of CO₂eq., which is approximately equivalent to 60% of the emissions from the MSW landfills. This corresponds to the 2030 GHG reduction target of Korea’s waste sector. This indicates that the application of active aeration to MSW landfills is essential for reducing GHG emissions from the waste sector. The calculated MCF of the landfill with a methane concentration of 5% or less under aerobic conditions was 0.31 to 0.34, which is lower than the MCF default value suggested in the IPCC guideline (i.e., 0.4). However, further research on MCF in aerobic landfill should be conducted.

Key Words

Greenhouse gas, IPCC guideline, Solid waste landfill, Active aeration, Methane correction factor

Eunil Cho , Qiyong Xu , Danling Xia , Jae Hac Ko

DOI:10.9786/kswm.2021.38.4.310

Abstract

One of the significant challenges of food waste anaerobic digestion (AD) is the negative effect of high NaCl concentrations. This study investigated the effects of NaCl fluctuation on the methane generation of food waste AD under thermophilic and mesophilic conditions. Particularly, the effects of the shock loading of high NaCl concentration with/ without water dilution treatment were investigated. Generally, the methane generation decreased with increasing NaCl concentration. In addition, the sensitivity of the thermophilic AD to NaCl concentrations (5-10 g/L) was higher than that of the mesophilic AD. Furthermore, with an increase in the NaCl concentration from 0 to 30 g/L, the accumulative methane volumes of the thermophilic reactors decreased from 210 to 45 mL/gVS, and those of the mesophilic reactors decreased from 265 to 67 mL/gVS. Additionally, the pH of digestate decreased with increasing NaCl concentration. In contrast, the concentrations of the chemical oxygen demand and volatile fatty acid increased with increasing NaCl concentration. These results indicated that a shock loading of NaCl significantly reduced methane generation. In addition, the methane generation rates could be recovered up to 64-72% using water dilution as a remedial measure. Further investigation using 16S rRNA analysis revealed that the predominant genus of the methanogens shifted from Methanoculleus to Methanosarcina after the removal of the osmotic stress using water dilution.

Key Words

Food waste, Methane generation, NaCl Inhibition, Anaerobic digestion

권은혜 Eunhye Kwon , 배지수 Jisu Bea , 김우일 Wooil Kim , 윤영삼 Youngsam Yoon , 이원석 Wonseok Lee , 박호연 Hoyeun Park

DOI:10.9786/kswm.2021.38.4.318

Abstract

Polychlorinated naphthalenes (PCNs), one of Persistent Organic Pollutants (POPs), and are colorless crystalline substances with similar structure and physical and chemical properties with PCB (polychlorinated biphenyl), and are produced by the chlorination of naphthalene. PCN is one of POPs are rarely degraded in the environment; consequently, they negatively impact the environment by threatening human health and the ecosystem. In this study, the potential of a stable treatment for lab-scale-incinerated waste containing PCNs was evaluated. For this study, waste containing PCNs were selected as the surface coating agent, mixed sample, and technical sample. The results revealed that when the PCNs concentration was 34.552 ~ 2,582.463 ng/g, the concentrations of Mono-CN and Tetra-CN were higher than those of other homologues. The incineration treatment conditions were derived by measuring three parts, after which the elemental composition was analyzed and the calorific value, theoretical air content, and residence time were calculated. Using the temperature of the target sample, thermogravimetric analysis revealed that the incineration treatment can be achieved at the incineration temperature of the existing incineration facility via weight change. Therefore, the incineration temperature was set between 850 and 1,100℃; however, the incineration temperature of the sample containing a high concentration of PCNs was set at 350, 500, 850, and 1,100℃. At 350 and 500℃, high concentrations of CO and NOx were observed, which could be attributed to incomplete combustion. Furthermore, heat-sensitive PCNs showed a de-chlorination reaction between 200 to 440℃. In addition, the decomposition rate (DRE) slightly increased according to the incineration temperature increase.

Key Words

PCNs, Lab-scale Reactor, Incineration

한상무 Sang Moo Han , 김도형 Do Hyung Kim , 김소희 So Hee Kim , 김홍민 Hong Min Kim , 정병곤 Byung Gon Jeong

DOI:10.9786/kswm.2021.38.4.330

Abstract

Various media were manufactured using different ratios of alum sludge obtained from a water purification plant, loess, and clay, and the properties of the media were investigated. The results revealed that the optimal compressive strength was achieved at a ratio of 15/65/20 (alum sludge/loess/clay). In addition, the absorption rate of the media increased with an increase in the quantity of alum sludge in the media. Furthermore, the scanning electron microscopy analysis of the pore structure of the media revealed that the optimal permeability was achieved at a ratio of 15/65/20. Additionally, the manufactured media satisfied the dissolution test of heavy metals regardless of the mixing ratio. Furthermore, at the optimal mixing ratio, the removal efficiency of phosphorus by the media increased with a decrease in the size of the media.

Key Words

Alum sludge, Loess, Clay, Phosphorus, Absorbent

이혜성 Hyesung Lee , 김용진 Yongjin Kim

DOI:10.9786/kswm.2021.38.4.337

Abstract

Tire particles account for a high proportion of emitted microplastics, and the quantity is increasing with an increase in the production of vehicles and tires. Such tire particles are present not only in roadsides, rainwater inlets, and sewage treatment facilities, but also in mud flats. Tire particles are introduced into water environment through the atmosphere and rainwater. In this study, the inflow of tire particles to water environment in Korea based on district was estimated using statistical data on roads and sewage management areas and previous studies. In addition, the quantity of tire particles generated by each type of vehicle and the ratio of the inflow of the generated tire particles to water environment based on the district and type of road and vehicle were reviewed. The results revealed that the quantity of tire particles generated in Korea was 49,995 t per year, and the quantity of tire particles generated based on the vehicle type was in the order of heavyweight truck > bus > passenger car > lightweight truck. In addition, the quantity of tire particles discharged to the atmosphere was 50-4,999 tonnes per year, and the quantity of tire particles retained on the ground surface was 44,995- 49,945 tonnes per year. Furthermore, the quantity of tire particles introduced to water environment was 12,897-24,241 tonnes per year, and the inflow to water based on the road type was in the order of other roads > national road > highway.

Key Words

Tire particles, Microplastics, Combined sewer, Separated sewer, Water environment

안조환 Johwan Ahn , 하승수 Seung-soo Ha

DOI:10.9786/kswm.2021.38.4.350

Abstract

Biosolids are physically or chemically stabilized organic solids derived from sewage treatment processes. In the last one year, municipal sewage sludge, which is treated using thermal hydrolysis, has been used as a raw material for export fertilizer. Thus, in this study, we investigated if the quality of biosolids recovered from sewage treatment plants equipped with both thermal hydrolysis and anaerobic digestion processes meets the Korean fertilizer raw material standards. The investigations revealed that the contents of heavy metals, Ni, Zn, and Al in biosolids were higher than the regulated standards; however, pathogens, such as Escherichia coli and Salmonella sp., were not observed in the biosolids. The results indicated that biosolids are inappropriate as a raw material for domestic fertilizer. Nevertheless, as biosolids can be used for manufacturing export fertilizer, it is necessary to establish the quality standards for toxic heavy metals, pathogens, and organic micropollutants present in biosolids for the protection of public health.

Key Words

Anaerobic digestion, Biosolids, Fertilizer, Municipal sewage sludge, Thermal hydrolysis

임성현 Sung-hyun Lim , 윤석표 Seok-pyo Yoon

DOI:10.9786/kswm.2021.38.4.357

Abstract

In this study, we developed an environmental assessment method to investigate permeable blocks prepared using recycled polyethylene terephthalate (PET) as a binder. First, Los Angeles abrasion test was conducted to simulate the surface abrasion caused by the long-term use of water-permeable block, and the number of rotations was 100-300. To separate the microplastics from the residual fragments of the degraded surface of the permeable block, the microplastics were subjected to a flotation process using calcium chloride as a sorting solvent. The obtained microplastics from the abrasion test was quantitatively and qualitatively analyzed using a particle size analyzer, microscopy, and Fourier transform-infrared spectroscopy. To obtain the extract, the permeable block was subjected to a leaching test, and the pH and Ca concentration were measured. The pH of the cement-based permeable block (10.79 ± 0.17) was higher than that of the PET-based permeable block (9.58 ± 0.23). In addition, the extracts of recycled PET- and cement-based permeable blocks were subjected to an acute toxicity test using Daphnia, and the results revealed that the toxic unit of the recycled PET permeable blocks was 0, whereas that of the cement-based permeable blocks was 1.98 ± 0.11.

Key Words

Recycled PET permeable block, LA abrasion test, FTIR, Leaching test, Acute toxicity test using Daphnia

윤종혁 Jonghyuk Yoon , 송형운 Hyoungwoon Song , 장은석 Eun-suk Jang

DOI:10.9786/kswm.2021.38.4.366

Abstract

With the depletion of fossil fuels, the use of new and renewable energy has attracted significant attention. Among various biomass fuels, wood pellets and chips are used as commercial fuels owing to their low water content compared to sewage sludge and food waste. Recently, the use of livestock manure as fuel has attracted significant owing to its ease of collection and transportation. However, the low economic feasibility of co-firing boiler, which is used to process livestock manure solid refuse fuel (SRF), has limited the further application of livestock manure. Therefore, the development of an efficient grate boiler for livestock-manure is highly needed. In this study, a three-dimensional computational fluid dynamics simulation was performed to evaluate the combustion performance of a livestock manure SRF grate furnace. To validate the numerical method, the numerical results of the temperature and species concentration at several monitoring points were compared to those of the experimental results. In addition, a parametric study was performed using various ratios of primary to assist air to understand the effects of air conditions on the overall combustion performance.

Key Words

Numerical study, Combustion characteristics, Livestock-manure, Computational fluid dynamics (CFD), Parametric study