홍인기 In-gi Hong , 김도완 Do-wan Kim , 배재근 Chae-gun Phae , 김대근 Dae-keun Kim

DOI:10.9786/kswm.2025.42.5.227

Abstract

Global plastic production has increased from approximately 100 million tons in 1989 to 400 million tons in 2022, driven by the material’s versatility. Consequently, efforts to manage plastic waste and promote the use of recycled materials are growing worldwide. In line with this trend, Korea is revising its subordinate legislation under the Act on the Promotion of Saving and Recycling of Resources to mandate that, starting in 2026, final producers manufacturing over 5,000 tons of beverage PET bottles annually must use at least 10% recycled content. This study aims to assess the current supply and demand of recycled plastic materials in Korea in preparation for the expansion of mandatory items and recycling rates. The analysis focuses on EPR-designated items with an existing recycling infrastructure and examines materialspecific data by identifying the composition ratio of each item. Four primary indicators were analyzed: treatment capacity, production capacity, actual usage volume of recycled materials, and pyrolysis oil output. The findings reveal several key insights: (1) Recycling capacity is largely concentrated on packaging materials, underscoring the need to expand infrastructure for other product types; (2) The usage rate of recycled content relative to shipment/import volume is relatively high for PE (29.4%) and PP (31.6%), but notably low for PET (0.3%) and PS (3.9%), primarily due to durability constraints and regulatory limitations; (3) Naphtha production from pyrolysis oil is projected to reach approximately 35.7 kt by 2026, indicating the need for additional processing capacity; (4) While PE and PP exhibit a relatively balanced supply-demand structure, PS and PVC require further strategies to address imbalances.

Key Words

Recycled plastic, Material type, Demand, Supply, Capacity

김주선 Jusun Kim , 김동욱 Dong-wook Kim , 임병현 Byung-hyun Lim , 우광재 Kwangjae Woo , 이재영 Jai-young Lee

DOI:10.9786/kswm.2025.42.5.239

Abstract

This study examined the application of microbubble (MB) technology to digestate effluent to improve anaerobic digestion performance at both laboratory and pilot scales. The implementation of MB technology increased digestion efficiency from 52% to 65% and raised the maximum methane (CH4) concentration by up to 10%. Additionally, COD, BOD, and suspended solids (SS) levels in the digestate decreased by 30-60%, while total nitrogen (T-N) and total phosphorus (T-P) were reduced by 25-40%. Sludge production declined by more than 20%, resulting in lower overall treatment costs. These findings suggest that MB-based solid-liquid separation can effectively mitigate the challenges posed by high-strength digestate, improve biogas quality, and serve as a promising technology for developing energy self-sufficient waste-to-energy facilities.

Key Words

Microbubbles (MB), Solid-liquid separation, Digestion, Digestate effluent, Biogas

이재희 Jae-hee Lee , 최장욱 Jang-wook Choi , 엄태인 Tae-in Ohm

DOI:10.9786/kswm.2025.42.5.246

Abstract

This study quantitatively analyzed the material and energy balance of an energy-self-sufficient waste treatment system by establishing a pilot-scale facility that integrates drying, pelletizing, combustion, and water treatment processes for spent coffee grounds (SCGs). SCGs, with a low recycling rate, were found to be suitable for this system due to their relatively consistent properties, such as ash and volatile matter content, and high calorific value despite high moisture content. The experimental results indicated that pellets made from SCG mixed with 10 wt.% citrus pressed cake had a durability of 98.3 wt.%, satisfying the Grade 1 quality standard for wood pellets. Specifically, 125 kg of pellets were combusted to recover energy for drying 400 kg (62.4 wt.% moisture content) of SCG, yielding 160 kg (6.1 wt.% moisture content) of dry powder (40.0% yield). The total energy consumed, including pellets and electricity, was 594 Mcal, which was 97 Mcal less than the 691 Mcal of energy supplied by dried pellets, confirming the system’s energy self-sufficiency. The heat recovery efficiency of the combustion process was 49.5%, the drying efficiency was 59.2%, and the heat loss was 273 Mcal. The amount of bottom ash generated was very low at 0.7 wt.% of the input material. The water treatment process showed high removal efficiencies of 96.7% for COD_Mn, 97.5% for TOC, and 99.6% for SS in 240 kg of condensate. These results provide quantitative evidence for the design and scale-up of energy recovery systems for highmoisture organic waste, securing both the energy independence and environmental feasibility of an SCG-based integrated process.

Key Words

Spent coffee grounds, Bio-solid fuel, Energy self-sufficient system, Pelletizing, Material and energy balance

임성원 Seongwon Im , 김명찬 Myungchan Kim , 김동훈 Dong-hoon Kim

DOI:10.9786/kswm.2025.42.5.259

Abstract

This study used the methane conversion factor (MCF) calculation model proposed in the Intergovernmental Panel on Climate Change (IPCC) 2019 Refinement guidelines to estimate methane emissions from pig slurry under Korean climatic and manure management conditions, using Tier 2 methodology. The results were then compared with those obtained using Tier 1 methodology. As the storage temperature increased from 5℃ to 35℃, the MCF increased from 6-24% to 100%. In addition, as the manure removal frequency was extended from once monthly to semiannually, the MCF increased by 1.8-4.0 times, and this effect intensified under lower-temperature conditions. When applying the Tier 2 methodology using locally derived parameters and the MCF model, the annual methane emissions from pig slurry were estimated to be approximately 40-99 ktons CH4/year, exceeding those calculated using the Tier 1 methodology by 1.2-2.9 times. This discrepancy arose due to the fact that the Tier 1 methodology relies solely on annual average temperature data and, therefore, does not reflect actual variations in temperature and nonlinear reaction kinetics during manure storage. These findings show that the Tier 2 methodology, which considers regional climatic conditions, more realistically estimates methane emissions from livestock manure. Future research should focus on developing an MCF calculation model based on field measurements, evaluating activation energy (E), and monitoring slurry temperature to improve the accuracy of national greenhouse gas inventories and establish Tier-2-level emission factors.

Key Words

Pig slurry, Methane conversion factor, Storage temperature, Manure removal frequency, Modeling