​Journal: Journal of Analytical and Applied Pyrolysis​Authors: Gihoon Kwon, Dong-Wan Cho, Kwangsuk Yoon, Eunji Kim, Jaewon Lee, Hocheol SongAbstract:The continuous growth of the global population and industries has led to the mass generation of plastic and industrial waste, posing significant environmental challenges due to their incompatibility with conventional waste management practices. This study investigates the thermochemical conversion of plastic (nylon-6) and industrial waste (red mud) into value-added products, presenting a waste-to-resource conversion strategy. Nylon-6 and red mud were co-pyrolyzed, resulting in a metal-carbon composite characterized as porous N-doped graphitic carbon with embedded Fe0 particles. Application of the composite to an amaranth solution demonstrated its ability to activate persulfate, facilitating amaranth oxidation at a rate (kobs = 1.78 min−1) significantly higher than other Fe-based catalysts. Quenching experiments verified the generation of OH· and SO4·- radicals during activation, with the latter playing a dominant role in amaranth degradation. The composite exhibited robust reusability, maintaining an amaranth removal efficiency of >80 % after five reaction cycles. Additionally, red mud significantly enhanced syngas (H2 and CO) generation from nylon-6, suggesting a catalytic effect. In conclusion, the proposed thermochemical approach offers a viable method for converting waste materials into valuable products, including environmental catalysts and gas fuels. Keywords: N-doped graphic carbon; Co-pyrolysis; Red mud; Plastic valorization; Persulfate activationDOI: https://doi.org/10.1016/j.jaap.2024.106619

​Journal: Energy​Authors: Dohee Kwon, Dongho Choi, Hocheol Song, Jechan Lee, Sungyup Jung, Eilhann E. KwonAbstract:Plastics have become an integral part of our daily lives owing to their exceptional physicochemical properties, such as durability, low density, and cost-effectiveness, compared to traditional materials. However, the escalating production of plastics has resulted in a proportional increase in waste generation. This paper proposes environmentally benign valorization/disposal methods for plastic waste, with a particular focus on adopting a pyrolysis process that utilizes CO2 as a strategic reaction medium. As a case study, polyoxymethylene (POM), a widely used engineering plastic, was valorized through CO2-mediated pyrolysis. This study experimentally demonstrates the mechanistic effectiveness of CO2 in expediting the reaction kinetics of the thermal decomposition, specifically dehydrogenation and deoxygenation, of volatile matter derived from POM. The results revealed that employing CO2 as a reactant in the two-stage pyrolysis at 500 °C produced 30.47 mmol more syngas than under inert conditions. In conclusion, the strategic utilization of a two-stage pyrolysis process at 500 °C with CO2 as the reactant has emerged as an effective approach to the valorization of POM. This study contributes to developing sustainable methods for managing plastic waste by addressing environmental concerns and the need for efficient material recovery. Keywords: Circular economy; Waste valorization; Pyrolysis; Carbon dioxide; PolyoxymethyleneDOI: https://doi.org/10.1016/j.energy.2024.132118

​Journal: Chemical Engineering Journal​Authors: Gihoon Kwon, Kwangsuk Yoon, Eilhann Kwon, Juyeong Park, Heuiyun Lee, Hocheol SongAbstract:The rapid expansion of the electronics industry has entailed unavoidable generation of electronic waste (e-waste) in a massive quantity. Although e-waste contains varying degrees of precious metals and rare earth elements, a substantial portion of e-waste is ended up in landfills and incineration facilities. These management practices preemptively eliminate the possibility of recovering those elements from e-waste and often lead to environmental contamination. Nonetheless, there has been a consistent increase in the global demand for those critical metals, resulting in a steady rise in their prices. To address this issue, researchers have put multifaceted efforts to reclaim e-waste as a renewable resource. Several metallurgical techniques have proven to be effective in refining precious and rare earth metals from e-waste. Besides, thermochemical process has been developed to convert plastic materials in e-waste into fuel gases and other value-added chemicals. These approaches contribute to establishing economic value-chain of e-waste. To this end, this review critically discusses up-to-date technical advancements in e-waste reclamation processes with an emphasis on their potential role in realizing a circular economy. Lastly, the studies on life-cycle assessment of e-waste are reviewed to assess the environmental and industrial consequences of current reclamation processes. Keywords: Electronic wastes; Metal recovery; Plastic valorization; Circular economy; Life-cycle assessment; E-waste recyclingElectronic wastes; Metal recovery; Plastic valorization; Circular economy; Life-cycle assessment; E-waste recyclingDOI: https://doi.org/10.1016/j.cej.2024.153154

​Journal: Journal of Industrial and Engineering Chemistry ​Authors: Gihoon Kwon, Naeun Kim, Kwangsuk Yoon, Juyeong Park, Dong-Wan Cho, Jörg Rinklebe, Hocheol SongAbstract:The presence of antibiotics in wastewater poses significant risks to ecosystem due to their persistence and role in fostering the development of antibiotic-resistant strains of bacteria. This study explores the thermochemical conversion of waste materials (nylon and red mud) into a carbon composite and evaluates its efficacy as a catalyst for advanced oxidation process to remove enrofloxacin in aqueous phase. The composite was produced by co-pyrolyzing nylon and red mud under an inert condition. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the composite consisted of graphitic C3N4 coated on red mud particles rich in Fe0 content (g-C3N4/Fe0). The thermogravimetric/gas analysis indicated that red mud enhanced the thermolytic kinetics of nylon, leading to an increase of syngas production. The resulting composite effectively catalyzed persulfate activation to drive enrofloxacin oxidation. Notably, the composite fabricated at 900 ˚C was more efficient in oxidizing enrofloxacin than other composites produced at 400 and 600 ˚C because of its high Fe0 content and the presence of pyridinic N. The composite also exhibited good reusability to sustain > 60% enrofloxacin removal even after 9 reaction cycles. This study proposes an eco-friendly waste valorization strategy to produce an environmental medium through a one-step process. Keywords: Pyrolysis; Co-pyrolysis; Waste-to-energy; Plastic valorization; PPCPsDOI: https://doi.org/10.1016/j.jiec.2024.05.053

Journal: Environmental Science and Technology Authors: Song H.; Carraway E.R.Abstract:Nanosized iron (<100 nm in diameter) was synthesized in the laboratory and applied to the reduction of eight chlorinated ethanes (hexachloroethane (HCA), pentachloroethane (PCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA), 1,1,2-trichloroethane (1,1,2-TCA), 1,1,1-trichloroethane (1,1,1-TCA), 1,2-dichloroethane (1,2-DCA), and 1,1-dichloroethane (1,1-DCA)) in batch reactors. Reduction of 1,1,1-TCA increased linearly with increasing iron loading between 0.01 and 0.05 g per 124 mL solution (0.08-0.4 g/L). Varying initial concentrations of PCA between 0.025 and 0.125 mM resulted in relatively constant pseudo-first-order rate constants, indicating PCA removal conforms to pseudo-first-order kinetics. The reduction of 1,1,2,2-TeCA decreased with increasing pH; however, dehydrohalogenation of 1,1,2,2-TeCA became important at high pH. All chlorinated ethanes except 1,2-DCA were transformed to less chlorinated ethanes or ethenes. The surface-area-normalized rate constants from first-order kinetics analysis ranged from <4 × 10-6 to 0.80 L m-2 h-1. In general, the reactivity increased with increasing chlorination. Among tri- and tetrasubstituted compounds, the reactivity was higher for compounds with chlorine atoms more localized on a single carbon (e.g., 1,1,1-TCA > 1,1,2-TCA). Reductive β-elimination was the major pathway for the chlorinated ethanes possessing α,β-pairs of chlorine atoms to form chlorinated ethenes, which subsequently reacted with nanosized iron. Reductive α-elimination and hydrogenolysis were concurrent pathways for compounds possessing chlorine substitution on one carbon only, forming less chlorinated ethanes. © 2005 American Chemical Society.Keywords: NoneDOI: https://doi.org/10.1021/es048262e

Journal: Environmental Engineering Science Authors: Song H.; Carraway E.R.Abstract:Dechlorination of three chlorinated methanes (CCl4, CHCl 3, CH2Cl2) was investigated using a nano-sized iron synthesized by borohydride reduction of Fe3+ under anaerobic conditions. When reacted with chlorinated methanes in batch reactors, nano-sized iron rapidly transformed CCl4 and CHCl3, but showed negligible reactivity toward CH2Cl2, giving the reactivity order of CCl4 > CHCl3 ≫ CH2Cl 2. CH4 was observed along with CH2Cl 2 in the reduction of CCl4 and CHCl3, and they are presumed to be generated via concerted reductive elimination steps involving carbene and charged radical species. Pathways for CH4 production from CCl4 and CHCl3 reductions are proposed. Evidence obtained from the study of several physicochemical factors including pH, initial concentration, hydrogen concentration, and metal loading indicates reduction of chlorinated methanes occurs via a direct electron transfer reduction mechanism, rather than an indirect mechanism involving reactive hydrogen species. In a comparative experiment with three types of commercial irons (Fisher, Connelly, and ARS) and CHCl3, nano-sized iron gave a surface area normalized rate constant (kSA) value of 5.6(±0.6) × 10-2 L/m2 · h, which is one order of magnitude greater than Fisher iron and two orders of magnitude greater than ARS and Connelly irons. This comparison of kSA values should be considered approximate due to large differences in metal loadings. © Mary Ann Liebert, Inc.Keywords: Carbene intermediates; Hydrogenolysis; Initial concentration; Metal Loading; Microscale iron; pH; Reductive dechlorination; Reductive eliminationDOI: https://doi.org/10.1089/ees.2006.23.272

Journal: Journal / American Water Works Association Authors: Hong Y.; Liu S.; Song H.; Karanfil T.Abstract:The literature reports significantly different patterns for haloacetic acid (HAA) formation kinetics during chloramination. This study systematically examines the routes of HAA formation and elucidates the cause(s) behind the inconsistencies and discrepancies reported for HAA formation patterns. Until now, it has been generally accepted that free chlorine that formed as a result of monochloramine decomposition was responsible for most of the HAA formation in a chloraminated water. However, laboratory experiments conducted in this research indicated that the direct reaction of monochloramine with dissolved organic matter plays the major role in HAA formation during chloramination. In addition, the authors showed that the use of ammonia chloride, which is recommended by the US Environmental Protection Agency as a quenching agent in method 552.3, may lead to overestimations of HAA concentrations in chloraminated water samples. Study findings should prove useful in devising HAA control strategies and developing mechanistic or empirical models of HAA formation.Keywords: NoneDOI: https://doi.org/10.1002/j.1551-8833.2007.tb08007.x

Journal: Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal Authors: Song H.; Kim Y.H.; Carraway E.R.Abstract:For nearly a decade the use of bimetallic reactive materials containing zero-valent iron has been investigated because of the substantial reaction rate enhancements and applicability to a broader range of contaminants compared to those materials in which iron is the only reactive metal. However, despite the knowledge gained regarding bimetallic treatment approaches, details of reaction pathways remain elusive. This paper presents a review of some fundamental processes and underlying reactions of bimetallic materials in order to provide a backdrop for interpreting reports of bimetallic material reactivity as well as understanding current approaches to improving, controlling, and utilizing their characteristics. © 2007 by the American Society of Civil Engineers. All Rights Reserved.Keywords: Chemical reactions; Copper; Halogen organic compounds; Hydrogen; Iron; MetalsDOI: https://doi.org/10.1061/9780784408810.ch12

Journal: Environmental Monitoring and Assessment Authors: Hur J.; Schlautman M.A.; Karanfil T.; Smink J.; Song H.; Klaine S.J.; Hayes J.C.Abstract:The Reedy River in South Carolina is affected by the urban area of Greenville, the third most populous city in the state, and by the effluents from two large-scale municipal wastewater treatment plants (WWTPs) located on the river. Riverine water chemistry was characterized using grab samples collected annually under spring season baseflow conditions. During the 4- year time period associated with this study, climatic variations included two severe drought spring seasons (2001 and 2002), one above-normal precipitation spring season (2003), and one below-normal precipitation spring season (2004). The influence of drought and human activities on the baseflow chemistry of the river was evaluated by comparing concentrations of dissolved anions, total metals, and other important water chemistry parameters for these different years. Concentrations of copper and zinc, common non-point source contaminants related to urban activities, were not substantially elevated in the river within the urban area under baseflow conditions when compared with headwater and tributary samples. In contrast, nitrate concentrations increased from 1.2-1.6 mg/l up to 2.6-2.9 mg/ l through the urban stream reach. Concentrations of other major anions (e.g., sulfate, nitrate) also increased along the reach, suggesting that the river receives continuous inputs of these species from within the urban area. The highest concentrations of major cations and anions typically were observed immediately downstream from the two WWTP effluent discharge locations. Attenuation of nitrate downstream from the WWTPs did not always track chloride changes, suggesting that nitrate concentrations were being controlled by biochemical processes in addition to physical processes. The relative trends in decreasing nitrate concentrations with downstream distance appeared to depend on drought versus non-drought conditions, with biological processes presumably serving as a more important control during non-drought spring seasons. © Springer Science + Business Media B.V. 2007.Keywords: Drought; Urban river; Urban watershed; Wastewater treatment; Water chemistryDOI: https://doi.org/10.1007/s10661-006-9513-1

Journal: Journal / American Water Works Association Authors: Hong Y.; Liu S.; Song H.; Hu J.; Ates N.; Karanfil T.Abstract:This study investigated how determination of haloacetic acid (HAA) in chloraminated samples was affected by use of ammonium chloride (NH 4Cl), the chlorine quenching agent recommended in US Environmental Protection Agency method 552.3. Alternative quenching agents and methods were also examined. Study results showed that using NH4Cl to preserve HAA samples obtained from chloraminated waters may result in positive errors for samples collected at short contact (or residence) time locations. The magnitude of these errors in practical applications will vary depending on several factors, including pH, reactivity of dissolved organic matter and concentration at the point of chloramination, and chlorine/ammonia application. Among various quenching agents or methods tested, sodium arsenite and stoichiometric amounts of sodium sulfate were found to be appropriate for chloramine samples but have some limitations for use in practical applications. Selection of sample quenching and preservation methods for HAA determination in chloramination systems must be carefully evaluated. In addition, better quenching methods for HAA determination in chloraminated waters are needed.Keywords: NoneDOI: https://doi.org/10.1002/j.1551-8833.2008.tb08145.x