Do-Yong Kim

Considering carbon neutrality and fossil fuel depletion, biomass is becoming increasingly important as a renewable and sustainable energy source. However, understanding of process-dependent characteristics relevant to char production remains limited. This study investigated the carbonization of mushroom waste medium (MWM) via conventional carbonization (CC; i.e., pyrolysis), hydrothermal carbonization (HTC), and microwave-assisted carbonization (MAC), and evaluated their suitability for desired char properties and target applications. For all methods, increasing reaction temperature led to carbon densification, with decreased oxygen and hydrogen contents and increased carbon and fixed carbon fractions. However, the extent of these transformations depended on the reaction environment. HTC achieved carbon enrichment and the highest higher heating value (HHV) at relatively low temperatures. In contrast, CC required higher temperatures to achieve comparable carbonization levels but showed a marked increase in BET surface area at higher temperatures. MAC exhibited intermediate characteristics under moderate conditions. HTC also facilitated potassium and chlorine removal, which may reduce operational issues during thermal utilization. These results indicate trade-offs among carbon densification, char yield, surface structure, and inorganic matter content. Rather than identifying a universally superior process, this study demonstrates that the suitability of each method depends on the desired properties and applications of MWM-derived char, providing a practical basis for appropriate process selection.

Indoor air pollution remains a major concern, with formaldehyde (HCHO) a primary contributor due to its long emission period and associated health risks, including skin allergies, coughing, and bronchitis. This study evaluated the adsorption performance and economic efficiency of various adsorbents (biochar, activated carbon, zeolites A, X, and Y) selected for HCHO removal. The impact of thermal treatment on adsorbent regeneration was also assessed. The experimental apparatus featured an adsorption column and HCHO concentration meter with an electrochemical sensor designed for adsorption analysis. Zeolite X exhibited the highest adsorption performance, followed by zeolite A, zeolite Y, activated carbon, and biochar. All adsorbents displayed increased HCHO removal rates with an extended length/diameter (L/D) ratio of the adsorption column. Zeolite A demonstrated the highest economic efficiency, followed by zeolite X, activated carbon, zeolite Y, and biochar. Higher L/D ratios improved economic efficiency and prolonged the replacement cycle (the optimal timing for adsorbent replacement to maintain high adsorption performance). Sensitivity analysis of adsorbent regeneration under varying thermal treatment conditions (150, 120, and 80 degrees C) and durations (60, 45, and 30 min) revealed minimal changes in adsorption efficiency (+/- 3%). The results indicated the potential of adsorbent regeneration under energy-efficient thermal treatment conditions (80 degrees C, 30 min). In conclusion, this study underscores the importance of a comprehensive assessment, considering factors such as adsorption performance, replacement cycle, economic efficiency, and regeneration performance for the selection of optimal adsorbents for HCHO adsorption and removal.Implications: This study underscores the importance of adsorption technology for the removal of formaldehyde and similar volatile organic compounds (VOCs), highlighting the potential of alternative adsorbents, such as environmentally friendly biochar, in addition to traditional strategies, such as activated carbon and zeolites. Our findings demonstrate the feasibility of adsorbent regeneration under energy-efficient thermal treatment conditions. These results hold promise for improving indoor air quality, reducing environmental pollutants, and enhancing responses to air contaminants like fine dust and VOCs.

This study explores the effects of hydrothermal carbonization (HTC) on the fuel properties of empty fruit bunches (EFB) by varying the reaction temperatures between the range of 180–300 °C. The improved properties of hydrochars following HTC were achieved by analyzing the changes in the physical and chemical properties of EFB. Moreover, it can save energy during treatment processes, in addition to evaluating the improvement of the biofuel stability based on the equilibrium moisture content and agglomeration. The results showed that the chemical structure of EFB decomposed owing to dehydration and decarboxylation reactions, leading to increased carbon and fixed carbon concentrations in the obtained hydrochar; and thus, an increased calorific value. Hydrochar generated during HTC exhibited chemical properties similar to those of conventional coal fuel. The optimal HTC reaction temperature range was ~230–250 °C. Based on the X-ray fluorescence results, hydrochar produced during HTC had smaller K and Cl contents and a smaller degree of agglomeration than the original sample, indicating that clinker production can be reduced by the HTC of EFB. The results of this study have significance in the utilization of unused waste biomass as an energy source that can replace fossil fuels.

This study aimed to evaluate the wind environment in step-up and step-down urban canyons through a computational numerical experiment using the computational fluid dynamics (CFD) model. Spatial structural conditions were considered according to the location of high-rise buildings, and the changing wind patterns inside canyons were compared and analyzed by varying the building heights. Under the step-up to step-down condition, wind velocity inside the canyon weakened, a vertical vortex formed, and vertical air flow separated; additionally, in shallow and deep canyons, wind velocity and detailed flow differed slightly according to each additional condition. For the step-down to step-up condition, the building located in the center appeared to be isolated, and a general wind environment phenomenon consistent with the step-up and step-down structures was observed. However, depending on the isolated area, an additional roof-top canyon was formed, and the wind field in the canyon was found to affect the wind velocity and detailed flow in other canyons. The wind velocity components of the inflow and outflow winds into the canyon differed based on the step-up to step-down or step-down to step-up conditions, and according to the conditions in the first and second canyons. Furthermore, the vertical wind velocity components were greatly affected by the step-up and step-down structures. Accordingly, the height and structural location of the building could affect various phenomena, such as the separation of vortices and air currents inside the canyon, and a variable wind environment was formed according to a series of conditions for the building.

We investigated the effects of wall- and tree-type fences on the airflow and fine particular matter (PM_2.5) concentration around a school using a computational fluid dynamics (CFD) model. First, we validated the simulated wind speeds and PM_2.5 concentrations against measured values, and the results satisfied the recommended criteria of the statistical validation indices used. Then, we evaluated the fence effects for 16 inflow directions by conducting numerical simulations with different fence types and heights. With east–southeasterly inflow, relatively high PM_2.5 from the road was transported to the school. However, the wall-type fence prevented the PM_2.5 from the road from entering the school, and the PM_2.5 concentration decreased significantly downwind of the fence. With east–northeasterly inflow, the horizontal wind speed decreased due to the drag caused by the tree-type fence, resulting in a shift in the flow convergence region. The PM_2.5 concentration decreased in the region of strengthened upward flow. This occurred because the number of pollutants transported from the background decreased. A comparison of the two fence types revealed that the effect of the tree-type fence on inbound pollutants was more significant, due to increased upward flows, than the effect of the wall-type fence.

We investigated the characteristics of surface wind speeds and temperatures predicted by the local data assimilation and prediction system (LDAPS) operated by the Korean Meteorological Administration. First, we classified automated weather stations (AWSs) into four categories (urban flat (Uf), rural flat (Rf), rural mountainous (Rm), and rural coastal (Rc) terrains) based on the surrounding land cover and topography, and selected 25 AWSs representing each category. Then we calculated the mean bias error of wind speed (WE) and temperature (TE) using AWS observations and LDAPS predictions for the 25 AWSs in each category for a period of 1 year (January–December 2015). We found that LDAPS overestimated wind speed (average WE = 1.26 m s⁻¹) and underestimated temperature (average TE = −0.63 °C) at Uf AWSs located on flat terrain in urban areas because it failed to reflect the drag and local heating caused by buildings. At Rf, located on flat terrain in rural areas, LDAPS showed the best performance in predicting surface wind speed and temperature (average WE = 0.42 m s⁻¹, average TE = 0.12 °C). In mountainous rural terrain (Rm), WE and TE were strongly correlated with differences between LDAPS and actual altitude. LDAPS underestimated (overestimated) wind speed (temperature) for LDAPS altitudes that were lower than actual altitude, and vice versa. In rural coastal terrain (Rc), LDAPS temperature predictions depended on whether the grid was on land or sea, whereas wind speed did not depend on grid location. LDAPS underestimated temperature at grid points on the sea, with smaller TE obtained for grid points on sea than on land.

Coastal debris has recently emerged as a serious environmental pollution problem. Coastal debris can be treated using pyrolysis because it consists mainly of combustible materials like plastics (e.g., polyethylene (PE), polypropylene (PP), nylon) and wood. In this study, the pyrolysis characteristics of coastal debris were fully utilized by applying their basic data to fuel production. The initial temperature increased from 330 °C to 380 °C for the nylon fishing net coastal debris sample, from 405.01 °C to 430.08 °C for the PE fishing net coastal debris sample, from 395.01 °C to 419.96 °C for the PP rope coastal debris sample, and from 114.95 °C to 115.02 °C for the wood (bamboo) coastal debris sample. The activation rate of the global activation energy and the pre-exponential factors rose with the increasing heating rate, complementing the reduction rate constant due to the larger growth of the exponential term due to the kinetic models used.