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Walter Den
Department of Science and Mathematics, Texas A&M University—San Antonio, One University Way, San Antonio, TX 78224, USA

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Review
Published: 19 May 2021 in Sustainability
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As the world human population and industrialization keep growing, the water availability issue has forced scientists, engineers, and legislators of water supply industries to better manage water resources. Pollutant removals from wastewaters are crucial to ensure qualities of available water resources (including natural water bodies or reclaimed waters). Diverse techniques have been developed to deal with water quality concerns. Carbon based nanomaterials, especially carbon nanotubes (CNTs) with their high specific surface area and associated adsorption sites, have drawn a special focus in environmental applications, especially water and wastewater treatment. This critical review summarizes recent developments and adsorption behaviors of CNTs used to remove organics or heavy metal ions from contaminated waters via adsorption and inactivation of biological species associated with CNTs. Foci include CNTs synthesis, purification, and surface modifications or functionalization, followed by their characterization methods and the effect of water chemistry on adsorption capacities and removal mechanisms. Functionalized CNTs have been proven to be promising nanomaterials for the decontamination of waters due to their high adsorption capacity. However, most of the functional CNT applications are limited to lab-scale experiments only. Feasibility of their large-scale/industrial applications with cost-effective ways of synthesis and assessments of their toxicity with better simulating adsorption mechanisms still need to be studied.

ACS Style

Mian Aslam; Hsion-Wen Kuo; Walter Den; Muhammad Usman; Muhammad Sultan; Hadeed Ashraf. Functionalized Carbon Nanotubes (CNTs) for Water and Wastewater Treatment: Preparation to Application. Sustainability 2021, 13, 5717 .

AMA Style

Mian Aslam, Hsion-Wen Kuo, Walter Den, Muhammad Usman, Muhammad Sultan, Hadeed Ashraf. Functionalized Carbon Nanotubes (CNTs) for Water and Wastewater Treatment: Preparation to Application. Sustainability. 2021; 13 (10):5717.

Chicago/Turabian Style

Mian Aslam; Hsion-Wen Kuo; Walter Den; Muhammad Usman; Muhammad Sultan; Hadeed Ashraf. 2021. "Functionalized Carbon Nanotubes (CNTs) for Water and Wastewater Treatment: Preparation to Application." Sustainability 13, no. 10: 5717.

Journal article
Published: 17 May 2021 in Journal of Water Process Engineering
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A new type of composite adsorbent, encapsulated chitosan-modified magnetic carbon nanotubes (CS/MWCNTs/Fe) beads were used to remove hexavalent chromium (Cr(VI)) from aqueous solutions in a fixed-bed column. Among the various combination of operating parameters, we obtain a maximum volume of treated effluent (210 mL) under the following conditions: flow rate, 1 mL min−1; bed height, 8 cm; feed Cr(VI) concentration, 30 mg L−1; and solution pH, 4.0 ± 0.2. The corresponding adsorption capacity was 1.54 mg g-1 and the overall Cr(VI) removal efficiency was 54 %. In characterizing the dynamics of the adsorption process and breakthrough profiles, we found that the Thomas model and the Yoon-Nelson model both accurately described the breakthrough curves under all experimental conditions, while the Adams-Bohart model was applicable only for an early phase of dynamic behavior CtC0≤0.5 of the CS/MWCNTs/Fe beads column. Columns with shorter bed heights favored the global mass transfer rate, especially during the early breakthrough periods. Moreover, the bed depth service time (BDST) model was validated experimentally, enabling the prediction of service time of the adsorption bed at different outlet concentrations using hypothetical flow rates and inlet concentrations. Scaled-up study was performed to observe the column performance at higher throughputs. The high selectivity of Cr(VI) adsorption in the simulated wastewater in the presence of other heavy metals (copper and cadmium) and background anion (phosphate) suggests the applicability of CS/MWCNTs/Fe beads for Cr(VI) removal from industrial effluents.

ACS Style

Mian Muhammad Ahson Aslam; Walter Den; Hsion-Wen Kuo. Removal of hexavalent chromium by encapsulated chitosan-modified magnetic carbon nanotubes: Fixed-bed column study and modelling. Journal of Water Process Engineering 2021, 42, 102143 .

AMA Style

Mian Muhammad Ahson Aslam, Walter Den, Hsion-Wen Kuo. Removal of hexavalent chromium by encapsulated chitosan-modified magnetic carbon nanotubes: Fixed-bed column study and modelling. Journal of Water Process Engineering. 2021; 42 ():102143.

Chicago/Turabian Style

Mian Muhammad Ahson Aslam; Walter Den; Hsion-Wen Kuo. 2021. "Removal of hexavalent chromium by encapsulated chitosan-modified magnetic carbon nanotubes: Fixed-bed column study and modelling." Journal of Water Process Engineering 42, no. : 102143.

Journal article
Published: 25 November 2020 in Journal of Water Process Engineering
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This work demonstrates the performance of a composite adsorbent encapsulated with chitosan (CS) and maghemite-doped multiwall carbon nanotubes (MWCNTs). Hexavalent chromium (CrVI) was used as the representative hazardous heavy metal to characterize the adsorption behavior of the composite beads. The chromium speciation chemistry combined with the chitosan surface chemistry rendered pH at 4 to be the optimized condition in which the uptake of CrVI was quantitatively most effective. The Langmuir isotherm with a maximum adsorption capacity of 119 mg g−1 at 298 K was observed. The CrVI adsorption studies using partial compositions of the beads further demonstrated the synergistic role of combining the surface properties of CS and MWCNTs. The CrVI removal efficiency increased from 82 % to 96 % as the CS contents doubled in the CS/MWCNTs/Fe beads. Kinetically, the pseudo-second-order model showed the best regression fit (r2 > 0.99) with the experimental data. The intra-particle diffusion model further elucidated that the multiphasic rate-limiting steps during CrVI adsorption included external mass transfer resistance and intra-particle diffusion. The thermodynamic parameters (ΔG, ΔH, ΔS) indicated the adsorption process was spontaneous and endothermic in the tested temperature range (298–313 K). The weak negative Gibbs free energy (ΔG < −20 kJ mol−1) suggested a spontaneous adsorption process governed by electrostatic adsorption. The evolution of CrIII indicates a possible charge transfer effect of Fe2+/Fe3+ mediated through conductive carbon nanotubes, leading to the reduction of CrVI. In five adsorption-desorption cycles, the CrVI removal efficiency of CS/MWCNTs/Fe beads remained about 80 % in adsorption capacity.

ACS Style

Mian Muhammad Ahson Aslam; Walter Den; Hsion-Wen Kuo. Encapsulated chitosan-modified magnetic carbon nanotubes for aqueous-phase CrVI uptake. Journal of Water Process Engineering 2020, 40, 101793 .

AMA Style

Mian Muhammad Ahson Aslam, Walter Den, Hsion-Wen Kuo. Encapsulated chitosan-modified magnetic carbon nanotubes for aqueous-phase CrVI uptake. Journal of Water Process Engineering. 2020; 40 ():101793.

Chicago/Turabian Style

Mian Muhammad Ahson Aslam; Walter Den; Hsion-Wen Kuo. 2020. "Encapsulated chitosan-modified magnetic carbon nanotubes for aqueous-phase CrVI uptake." Journal of Water Process Engineering 40, no. : 101793.

Journal article
Published: 03 July 2020 in ECS Journal of Solid State Science and Technology
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This review paper focuses on the recent knowledge about our understanding of airborne molecular contamination (AMC) and its impact on 300-mm wafer fabrication processes. The adverse impacts on process materials by both organic and inorganic micro-contaminants, and evidence of cross-contamination between processed wafers and the mainstream wafer handling tools, are two areas of discussion for the study. The review also aims to re-frame the industrial guideline for AMC from chemical-based to risk-based approach, which substantiates the potential impacts of individual families of AMCs that have been well-documented. This approach resonates well with the new AMC classification method recently proposed by the International Roadmap of Devices and Systems (IRDS), building on new knowledge of AMC that emerged over time with the advances of analytical and testing capability. The review also brings forth the impact of moisture, the mere presence of which can compromise the integrity of device structures. However, moisture is especially detrimental in the presence of other inorganic ions to trigger unwanted reactions with surface materials. Methods developed to minimize the micro-contaminants and moisture during wafer handling and storage are also reviewed.

ACS Style

Walter Den; Shih-Cheng Hu; Cesar M. Garza; Omid Ali Zargar. Review—Airborne Molecular Contamination: Recent Developments in the Understanding and Minimization for Advanced Semiconductor Device Manufacturing. ECS Journal of Solid State Science and Technology 2020, 9, 064003 .

AMA Style

Walter Den, Shih-Cheng Hu, Cesar M. Garza, Omid Ali Zargar. Review—Airborne Molecular Contamination: Recent Developments in the Understanding and Minimization for Advanced Semiconductor Device Manufacturing. ECS Journal of Solid State Science and Technology. 2020; 9 (6):064003.

Chicago/Turabian Style

Walter Den; Shih-Cheng Hu; Cesar M. Garza; Omid Ali Zargar. 2020. "Review—Airborne Molecular Contamination: Recent Developments in the Understanding and Minimization for Advanced Semiconductor Device Manufacturing." ECS Journal of Solid State Science and Technology 9, no. 6: 064003.

Review article
Published: 13 December 2019 in Journal of Cleaner Production
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This study explores the environmental and energy benefits of biomass residues, including crop residues and agricultural waste, for the production of renewable energy in the form of biochar as fuel, in order to offer recommendations for policy makers, by reviewing information regarding the key environmental issues associated with the implementation of the systems. The highest environmental benefits for biochar-to-fuel systems were most observed in reduction of global warming potentials (i.e., carbon abatement), particularly for those integrated with combined heat and power technology, or for those incorporating electricity offsets from biochar combustion and co-firing. But all of these practices come at the cost of hidden environmental burdens, such as elevations in eutrophication, acidification, carcinogens and ecotoxicity impacts, as a consequence from land use change, additional infrastructure requirement or additional fertilizer application connected to biochar production or post-treatment. Other notable challenges, including regional availability of biomass residues, improper management of the residues, limited economic incentives, low energy efficiency and synergies, as well as mistreating adverse impacts from indirect land use change, were discussed. This suggests the flexibility to adjust the biomass-biochar ratio to optimize desired energy yields, carbon abatement and environmental beneficial objectives. Comprehensive analysis of the trade-offs between energy yields, carbon abatement and other associated environmental impacts is therefore recommended for future studies. Future studies in this field are also advised to explore the solution and to develop methodologies capable of quantifying the impacts and other equally relevant trade-offs, to better reflect the changes in real-world trends for decision making.

ACS Style

Mengshan Lee; Yi-Li Lin; Pei-Te Chiueh; Walter Den. Environmental and energy assessment of biomass residues to biochar as fuel: A brief review with recommendations for future bioenergy systems. Journal of Cleaner Production 2019, 251, 119714 .

AMA Style

Mengshan Lee, Yi-Li Lin, Pei-Te Chiueh, Walter Den. Environmental and energy assessment of biomass residues to biochar as fuel: A brief review with recommendations for future bioenergy systems. Journal of Cleaner Production. 2019; 251 ():119714.

Chicago/Turabian Style

Mengshan Lee; Yi-Li Lin; Pei-Te Chiueh; Walter Den. 2019. "Environmental and energy assessment of biomass residues to biochar as fuel: A brief review with recommendations for future bioenergy systems." Journal of Cleaner Production 251, no. : 119714.

Journal article
Published: 04 December 2019 in Scientific Reports
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Tetraoxy-anion of iron in +6 oxidation state (FeVIO42−, FeVI), commonly called ferrate, has shown tremendous potential as a green oxidative agent for decontaminating water and air. Encapsulation of solid potassium salt of ferrate (K2FeO4) circumvents the inherent drawbacks of the instability of ferrate under humid conditions. In the encapsulated strategy, controlled release without exposing the solid ferrate to the humid environment avoids self-decomposition of the oxidant by water in the air, and the ferrate is mostly used to decontaminate water efficiently. This study demonstrated the formulation of oxidative microcapsules with natural materials present in chitosan, whose release rate of the core material can be controlled by the type of intermediate hydrocarbon layer and the pH-dependent swelling of chitosan shell. The pH played a pivotal role in swelling chitosan shell and releasing the core oxidant. In a strong acidic solution, chitosan tended to swell quickly and release FeVI at a faster rate than under neutral conditions. Additionally, among the several long-chain hydrocarbon compounds, oleic acid exhibited the strongest “locking” effect when applied as the intermediate layer, giving rise to the slow release of FeVI. Coconut oil and mineral oil, in comparison, allowed FeVI to penetrate the layer within shorter lengths of time and showed comparable degrees of degradation of target contaminant, methylene orange, under ambient temperature and near-neutral conditions. These findings have practical ramifications for remediating environmental and industrial processes.

ACS Style

Bo-Yen Chen; Hsuen-Wen Kuo; Virender Sharma; Walter Den. Chitosan Encapsulation of FerrateVI for Controlled Release to Water:Mechanistic Insights and Degradation of Organic Contaminant. Scientific Reports 2019, 9, 1 -11.

AMA Style

Bo-Yen Chen, Hsuen-Wen Kuo, Virender Sharma, Walter Den. Chitosan Encapsulation of FerrateVI for Controlled Release to Water:Mechanistic Insights and Degradation of Organic Contaminant. Scientific Reports. 2019; 9 (1):1-11.

Chicago/Turabian Style

Bo-Yen Chen; Hsuen-Wen Kuo; Virender Sharma; Walter Den. 2019. "Chitosan Encapsulation of FerrateVI for Controlled Release to Water:Mechanistic Insights and Degradation of Organic Contaminant." Scientific Reports 9, no. 1: 1-11.

Journal article
Published: 18 November 2019 in Sustainability
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The post-Kyoto Protocol era has seen a transition to focus on the development of a renewable energy (RE) market as a primary instrument to reduce greenhouse gas (GHG) emissions worldwide. This paper analyses the development of GHG reduction and RE market in China, Japan, and Taiwan that are geographically proximate but socioeconomically diverse, and each plays a different but significant role in the world’s economy. By deploying a consolidated model incorporating the key components of market drivers underlying the goal of achieving GHG reduction, we threaded through the policy- and market-instruments implemented for each of the case studies over the past 20 years using the model. One commonality is that subsidiary schemes in the form of feed-in tariffs have served as an effective policy tool to boost the growth of renewable energy installations, though the worsening financial burden renders this path unsustainable. Over-reliance on feed-in-tariff schemes may have also impeded the liberation of an energy market pivotal to the success of elevating RE portfolio through trading mechanisms. What followed were the implementations of renewable energy certificate (REC) systems that have experienced various roadblocks leading to failures of the certificate market. By understanding the paths engaged in each of the cases, a conceptualized strategy depicted by the consolidated model is proposed to show the links between a renewable market and a carbon market. The framework would expedite the trading of RECs and carbon credits to accelerate the attainment of GHG emission reduction goals.

ACS Style

Jules Chuang; Hsing-Lung Lien; Akemi Kokubo Roche; Pei-Hsuan Liao; Walter Den. Consolidated Climate Markets Mechanism Analysis—Case Studies of China, Japan, and Taiwan. Sustainability 2019, 11, 6478 .

AMA Style

Jules Chuang, Hsing-Lung Lien, Akemi Kokubo Roche, Pei-Hsuan Liao, Walter Den. Consolidated Climate Markets Mechanism Analysis—Case Studies of China, Japan, and Taiwan. Sustainability. 2019; 11 (22):6478.

Chicago/Turabian Style

Jules Chuang; Hsing-Lung Lien; Akemi Kokubo Roche; Pei-Hsuan Liao; Walter Den. 2019. "Consolidated Climate Markets Mechanism Analysis—Case Studies of China, Japan, and Taiwan." Sustainability 11, no. 22: 6478.

Journal article
Published: 01 July 2019 in Future Generation Computer Systems
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ACS Style

Chao-Tung Yang; Shuo-Tsung Chen; Walter Den; Yun-Ting Wang; Endah Kristiani. Implementation of an Intelligent Indoor Environmental Monitoring and management system in cloud. Future Generation Computer Systems 2019, 96, 731 -749.

AMA Style

Chao-Tung Yang, Shuo-Tsung Chen, Walter Den, Yun-Ting Wang, Endah Kristiani. Implementation of an Intelligent Indoor Environmental Monitoring and management system in cloud. Future Generation Computer Systems. 2019; 96 ():731-749.

Chicago/Turabian Style

Chao-Tung Yang; Shuo-Tsung Chen; Walter Den; Yun-Ting Wang; Endah Kristiani. 2019. "Implementation of an Intelligent Indoor Environmental Monitoring and management system in cloud." Future Generation Computer Systems 96, no. : 731-749.

Journal article
Published: 26 December 2018 in Water-Energy Nexus
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Semiconductors are enabling technologies that drive today’s information economy by producing a broad spectrum of microelectronic consumer products including computers, flat-panel displays, sensors, storage devices, and lighting devices. Manufacturing of these semiconductor devices and products is capital and resources intensive and typically operates with either a vertically integrated manufacturing mode or with a cluster of supply-chain partnering companies in the vicinity of each other. Our research group has previously reported the water recycling and reuse efficiencies of “fabs” in the Science Parks in Taiwan (Lin et al., Res. Cons. Recycl. 2015), which exemplify this unique cluster of tech-manufacturing fabs demanding intensive supply of water and energy. We extend our discussion by summarizing the status of water consumption of major semiconductor and optomicroelectronic plants, and the industry’s collective and individual water reuse goals. Though the geographical location of fabs plays an important part of the water reuse efficiency, the industry generally displays a strong urgency to use water responsibly to maintain corporates’ competitiveness and to effectively manage the risks associated with water shortage. Additionally, the examination of water and energy expenditures of semiconductor fabs indicated a close water-energy relationship in the compartment of ultrapure water production process. The energy needed to treat, recycle and reuse spent water is secondary as compared to the energy demand for manufacturing processes. Using the industrial cluster in Taiwan as an example to illustrate the potential of improve water reuse through collaborative schemes, we conducted a survey-based study to assess how the industry perceived the proposed “inter-plants” and “inter-park” schemes designed to create a reclaimed water trading mechanism in place of the existing “in-plant” practice of water reclamation. Respondents showed an overall positive perception to such schemes on the basis of reducing water and energy demands in a cost-effective manner. The cost of water supply was a dominant factor in the perceived extent of benefits.

ACS Style

Walter Den; Chih-Hao Chen; Yung-Chien Luo. Revisiting the water-use efficiency performance for microelectronics manufacturing facilities: Using Taiwan’s Science Parks as a case study. Water-Energy Nexus 2018, 1, 116 -133.

AMA Style

Walter Den, Chih-Hao Chen, Yung-Chien Luo. Revisiting the water-use efficiency performance for microelectronics manufacturing facilities: Using Taiwan’s Science Parks as a case study. Water-Energy Nexus. 2018; 1 (2):116-133.

Chicago/Turabian Style

Walter Den; Chih-Hao Chen; Yung-Chien Luo. 2018. "Revisiting the water-use efficiency performance for microelectronics manufacturing facilities: Using Taiwan’s Science Parks as a case study." Water-Energy Nexus 1, no. 2: 116-133.

Journal article
Published: 01 November 2018 in Sustainable Environment Research
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Energy generation contributes nearly 40% of global greenhouse gas (GHG) emissions, and half of energy generated is purchased and used by industrial or commercial entities (Scope 2 category emission). Other than conserving energy and upgrading energy efficiency to reduce GHG emissions, these Scope 2 entities can switch to low-carbon electricity generated by renewable sources, whether through on-site installations or through energy products purchased. An electricity tracking and certification framework, such as the renewable energy certificate (REC), can be a powerful policy instrument to promote the acquisition of low-carbon electricity by the Scope 2 users. Designing, implementing, and regulating a REC framework must be meticulous in the determination of the electricity emission factor (in CO2 equivalent per unit power generated). This article uses several simplified scenarios to illustrate the advantage of implementing a trackable REC system to avoid the “free-rider effect” in the electricity market, and the proper accounting mechanism for the inclusion of onsite installations of renewable energy to eliminate the “outsider effect”. Still in its early phase of implementing a REC instrument to reach the GHG emission reduction goal, Taiwan has a chance for successful transition from the existing fossil fuel-rich energy portfolio to a low-carbon one, through reforming its energy infrastructure and introducing incentive-driven policies. Therefore, this paper also provides constructive recommendations to the policy-makers on the deployment of the REC system.

ACS Style

Jules Chuang; Hsing-Lung Lien; Walter Den; Luvian Iskandar; Pei-Hsuan Liao. The relationship between electricity emission factor and renewable energy certificate: The free rider and outsider effect. Sustainable Environment Research 2018, 28, 422 -429.

AMA Style

Jules Chuang, Hsing-Lung Lien, Walter Den, Luvian Iskandar, Pei-Hsuan Liao. The relationship between electricity emission factor and renewable energy certificate: The free rider and outsider effect. Sustainable Environment Research. 2018; 28 (6):422-429.

Chicago/Turabian Style

Jules Chuang; Hsing-Lung Lien; Walter Den; Luvian Iskandar; Pei-Hsuan Liao. 2018. "The relationship between electricity emission factor and renewable energy certificate: The free rider and outsider effect." Sustainable Environment Research 28, no. 6: 422-429.

Original manuscript
Published: 05 October 2018 in Environmental Progress & Sustainable Energy
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The adsorption equilibrium isotherms as well as gas sensing of three chlorinated phenolic compounds (CPCs) including phenol, 2‐chlorophenol, and 2,4‐dichlorophenol by acid‐functionalized carbon nanotube (CNT) membrane were studied. CNTs were synthesized via floating catalyst chemical vapor deposition method at 800°C and then functionalized with a mixture of HNO3 and H2SO4. The functionalized CNTs were vacuum filtered to form CNT membranes. The adsorption isotherm followed the Langmuir adsorption model better than the Freundlich model, suggesting monolayer adsorption. The maximum adsorption capacities were found to be 61.35, 93.46, and 104.17 mg g−1 for phenol, 2‐chlorophenol, and 2,4‐dichlorophenol, respectively. The desorption energy determined via thermogravimetric analysis indicates that adsorption of all three CPCs onto the CNT membranes belonged to chemisorption type. For the gas sensing test, the CNT membrane showed fast response to the tested CPCs with good stability and repeatability. The sensitivity values obtained were 5.39 × 10−2, 3.35 × 10−2 and 2.58 × 10−2 for 2,4‐dichlorophenol, 2‐chlorophenol, and phenol, respectively. It is noteworthy that the adsorption capacity and sensitivity of the CNT membrane to the target gases increased with the increase in the number of chlorine atoms in the phenolic compounds.

ACS Style

Ekkachai Kanchanatip; Sarttrawut Tulaphol; Walter Den; Nurak Grisdanurak; Hsin-Yuan Miao; Mi Yan. Sensing and adsorption study of gaseous phase chlorophenols on functionalized carbon nanotube membrane. Environmental Progress & Sustainable Energy 2018, 38, S315 -S322.

AMA Style

Ekkachai Kanchanatip, Sarttrawut Tulaphol, Walter Den, Nurak Grisdanurak, Hsin-Yuan Miao, Mi Yan. Sensing and adsorption study of gaseous phase chlorophenols on functionalized carbon nanotube membrane. Environmental Progress & Sustainable Energy. 2018; 38 (s1):S315-S322.

Chicago/Turabian Style

Ekkachai Kanchanatip; Sarttrawut Tulaphol; Walter Den; Nurak Grisdanurak; Hsin-Yuan Miao; Mi Yan. 2018. "Sensing and adsorption study of gaseous phase chlorophenols on functionalized carbon nanotube membrane." Environmental Progress & Sustainable Energy 38, no. s1: S315-S322.

Journal article
Published: 01 June 2018 in Water-Energy Nexus
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The risk of water shortage has been posing as a threat to water demanding industries in Taiwan, including the high-tech industries where ultrapure water is needed for the production of microchips. Such risks are especially unpredictable in the age of climate change, where more frequent extreme climate events such as prolonged droughts have sent these industries scrambling for securing water supply at a very high cost. The national policy also mandates strict water recycling standards for these high-tech plants, while the risk of water supply shortage also forces the industry to be water-conscious. However, most plants set their water recycling strategies based on experience or “rules of thumb” practices, without implementing optimization tools that can help making decisions in a more scientific approach. In this study we applied linear programming technique to optimize the water recovery path for a microchip assembly plant. A water balance diagram was formulated and completed to determine the existing water recycling performance, and the data was converted to a water flow network. The water flow network was then derived with a mathematical model to formulate a linear optimization problem. The proposed linear programming model is composed of mass balance constraints, unit specification constraints, capacity constraints as well as water quality constraints (discharge limits). The linear programming method was effectively appplied to improve the efficiency of water reuse. With the installation of the regeneration units, an increase of ∼40.1% in the volume of reused water was predicted. The results from water cost structure also indicated that, at higher water tariff, water reuses through reclaiming and generating spent effluents can alleviate the overall water consumption costs.

ACS Style

Bo-Shuan Lu; Mengshan Lee; Shuo-Tsung Chen; Chih-Hao Chen; Yung-Chien Luo; Walter Den. Strategic optimization of water reuse in wafer fabs via multi-constraint linear programming technique. Water-Energy Nexus 2018, 1, 86 -96.

AMA Style

Bo-Shuan Lu, Mengshan Lee, Shuo-Tsung Chen, Chih-Hao Chen, Yung-Chien Luo, Walter Den. Strategic optimization of water reuse in wafer fabs via multi-constraint linear programming technique. Water-Energy Nexus. 2018; 1 (1):86-96.

Chicago/Turabian Style

Bo-Shuan Lu; Mengshan Lee; Shuo-Tsung Chen; Chih-Hao Chen; Yung-Chien Luo; Walter Den. 2018. "Strategic optimization of water reuse in wafer fabs via multi-constraint linear programming technique." Water-Energy Nexus 1, no. 1: 86-96.

Review article
Published: 27 April 2018 in Frontiers in Chemistry
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Anthropogenic climate change, principally induced by the large volume of carbon dioxide emission from the global economy driven by fossil fuels, has been observed and scientifically proven as a major threat to civilization. Meanwhile, fossil fuel depletion has been identified as a future challenge. Lignocellulosic biomass in the form of organic residues appears to be the most promising option as renewable feedstock for the generation of energy and platform chemicals. As of today, relatively little bioenergy comes from lignocellulosic biomass as compared to feedstock such as starch and sugarcane, primarily due to high cost of production involving pretreatment steps required to fragment biomass components via disruption of the natural recalcitrant structure of these rigid polymers; low efficiency of enzymatic hydrolysis of refractory feedstock presents a major challenge. The valorization of lignin and cellulose into energy products or chemical products is contingent on the effectiveness of selective depolymerization of the pretreatment regime which typically involve harsh pyrolytic and solvothermal processes assisted by corrosive acids or alkaline reagents. These unselective methods decompose lignin into many products that may not be energetically or chemically valuable, or even biologically inhibitory. Exploring milder, selective and greener processes, therefore, has become a critical subject of study for the valorization of these materials in the last decade. Efficient alternative activation processes such as microwave- and ultrasound irradiation are being explored as replacements for pyrolysis and hydrothermolysis, while milder options such as advanced oxidative and catalytic processes should be considered as choices to harsher acid and alkaline processes. Herein, we critically abridge the research on chemical oxidative techniques for the pretreatment of lignocellulosics with the explicit aim to rationalize the objectives of the biomass pretreatment step and the problems associated with the conventional processes. The mechanisms of reaction pathways, selectivity and efficiency of end-products obtained using greener processes such as ozonolysis, photocatalysis, oxidative catalysis, electrochemical oxidation, and Fenton or Fenton-like reactions, as applied to depolymerization of lignocellulosic biomass are summarized with deliberation on future prospects of biorefineries with greener pretreatment processes in the context of the life cycle assessment.

ACS Style

Walter Den; Virender K. Sharma; Mengshan Lee; Govind Nadadur; Rajender S. Varma. Lignocellulosic Biomass Transformations via Greener Oxidative Pretreatment Processes: Access to Energy and Value-Added Chemicals. Frontiers in Chemistry 2018, 6, 141 .

AMA Style

Walter Den, Virender K. Sharma, Mengshan Lee, Govind Nadadur, Rajender S. Varma. Lignocellulosic Biomass Transformations via Greener Oxidative Pretreatment Processes: Access to Energy and Value-Added Chemicals. Frontiers in Chemistry. 2018; 6 ():141.

Chicago/Turabian Style

Walter Den; Virender K. Sharma; Mengshan Lee; Govind Nadadur; Rajender S. Varma. 2018. "Lignocellulosic Biomass Transformations via Greener Oxidative Pretreatment Processes: Access to Energy and Value-Added Chemicals." Frontiers in Chemistry 6, no. : 141.

Original article
Published: 12 March 2018 in Journal of Medical and Biological Engineering
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The improvement of environmental quality is aligned with the betterment of life quality. Poor air quality has a greatest impact on people health, it links to cancer, long-term harm to cardiovascular and respiratory systems. Conversely, safe air quality free of harmful gases such as formaldehyde, volatile organic compounds and carbon monoxide helps to prevent disease and other health problems. The application of information technology can greatly enhance the effectiveness of ensuring good air quality. Therefore, the implementation of environmental quality and harmful gases monitoring system is beneficial to manage indoor air quality. In this work, we built an environment quality monitoring system, which can adjust the indoor air quality and monitor the concentration of formaldehyde, volatile organic compounds and carbon monoxide. If the environment comfort value is out of the standard, the system will give notification if the concentration of harmful gases exceeds the standard, and activates air ventilation and purification devices. With these real-time data, the proposed system can help people make right and timely decisions, and act in time to maintain a healthy environment in the monitored area.

ACS Style

Chao-Tung Yang; Shuo-Tsung Chen; Chih-Hung Chang; Walter Den; Chia-Cheng Wu. Implementation of an Environmental Quality and Harmful Gases Monitoring System in Cloud. Journal of Medical and Biological Engineering 2018, 39, 456 -469.

AMA Style

Chao-Tung Yang, Shuo-Tsung Chen, Chih-Hung Chang, Walter Den, Chia-Cheng Wu. Implementation of an Environmental Quality and Harmful Gases Monitoring System in Cloud. Journal of Medical and Biological Engineering. 2018; 39 (4):456-469.

Chicago/Turabian Style

Chao-Tung Yang; Shuo-Tsung Chen; Chih-Hung Chang; Walter Den; Chia-Cheng Wu. 2018. "Implementation of an Environmental Quality and Harmful Gases Monitoring System in Cloud." Journal of Medical and Biological Engineering 39, no. 4: 456-469.

Review
Published: 01 November 2017 in Applied Energy
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ACS Style

Mengshan Lee; Arturo A. Keller; Pen-Chi Chiang; Walter Den; Hongtao Wang; Chia-Hung Hou; Jiang Wu; Xin Wang; Jinyue Yan. Water-energy nexus for urban water systems: A comparative review on energy intensity and environmental impacts in relation to global water risks. Applied Energy 2017, 205, 589 -601.

AMA Style

Mengshan Lee, Arturo A. Keller, Pen-Chi Chiang, Walter Den, Hongtao Wang, Chia-Hung Hou, Jiang Wu, Xin Wang, Jinyue Yan. Water-energy nexus for urban water systems: A comparative review on energy intensity and environmental impacts in relation to global water risks. Applied Energy. 2017; 205 ():589-601.

Chicago/Turabian Style

Mengshan Lee; Arturo A. Keller; Pen-Chi Chiang; Walter Den; Hongtao Wang; Chia-Hung Hou; Jiang Wu; Xin Wang; Jinyue Yan. 2017. "Water-energy nexus for urban water systems: A comparative review on energy intensity and environmental impacts in relation to global water risks." Applied Energy 205, no. : 589-601.

Journal article
Published: 01 June 2016 in Bioresource Technology
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This study characterized the fouling of a novel circular-disc ultrafiltration membrane in a submerged bioreactor system to harvest Arthrospira maxima cells. Flux-stepping study showed that the value of critical flux was below the smallest flux tested at 28.8 l m−2 h−1, and that the membrane was to operate above the critical flux to sustain the necessary rate of cell concentration. The membrane with similar pore size but greater pore density experienced not only lesser degree of total resistance, but also possessed smaller fraction of irreversible resistance. Membrane fouling was mainly attributed to fragmented cells rather than to soluble or extracellular polymeric substances. Furthermore, flux recovery studies demonstrated that membrane relaxation and surface cleaning could partially recover fluxes for both low (6 g l−1) and high (40 g l−1) cell densities, whereas backwashing could fully recover fluxes. Calculation of energy consumption and cell harvesting productivity also favoured membrane filtration with backwashing.

ACS Style

Ekkachai Kanchanatip; Bo-Rung Su; Sarttrawut Tulaphol; Walter Den; Nurak Grisdanurak; Chi-Chang Kuo. Fouling characterization and control for harvesting microalgae Arthrospira (Spirulina) maxima using a submerged, disc-type ultrafiltration membrane. Bioresource Technology 2016, 209, 23 -30.

AMA Style

Ekkachai Kanchanatip, Bo-Rung Su, Sarttrawut Tulaphol, Walter Den, Nurak Grisdanurak, Chi-Chang Kuo. Fouling characterization and control for harvesting microalgae Arthrospira (Spirulina) maxima using a submerged, disc-type ultrafiltration membrane. Bioresource Technology. 2016; 209 ():23-30.

Chicago/Turabian Style

Ekkachai Kanchanatip; Bo-Rung Su; Sarttrawut Tulaphol; Walter Den; Nurak Grisdanurak; Chi-Chang Kuo. 2016. "Fouling characterization and control for harvesting microalgae Arthrospira (Spirulina) maxima using a submerged, disc-type ultrafiltration membrane." Bioresource Technology 209, no. : 23-30.

Journal article
Published: 25 April 2016 in International Journal of Environmental Science and Technology
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Multi-walled carbon nanotubes (MWCNTs) embedded in SiO2 particles were prepared through the floating-catalyst chemical vapor deposition method. The parameters reaction time and flow rate of the carbon source (CH4) were studied to obtain optimum conditions for MWCNT synthesis. The obtained MWCNTs were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy to confirm their morphology and crystallinity. The optimum conditions were a CH4 flow rate of 100 ml/min in a H2–Ar mixture at a flow rate of 500 ml/min and a reaction time of 20 min. Under these conditions, MWCNTs with average outer and inner diameters of around 50 and 10 nm, respectively, were obtained. SiO2 particles with embedded MWCNTs were studied for their adsorption of gaseous chlorinated phenolic compounds (CPCs), with emphasis on the effect of number of chlorine substituents. The CPC compounds of 2-chlorophenol (CP) and 2,4-dichlorophenol (DCP) were compared against phenol (P). Adsorption of P and CPCs on the particles fit well the Langmuir isotherm. The adsorption capacities of P, CP, and DCP on SiO2 particles with embedded MWCNTs were found to be 3.12, 13.83, and 44.25 mg/g, respectively. Desorption activation energy was determined by thermogravimetric analysis. Chlorine substitution on P changed the adsorption process from physical to chemical adsorption. The particles showed high potential for use as a pre-concentration unit for solid-phase microextraction.

ACS Style

Sarttrawut Tulaphol; S. Bunsan; E. Kanchanatip; H.-Y. Miao; N. Grisdanurak; W. Den. Influence of chlorine substitution on adsorption of gaseous chlorinated phenolics on multi-walled carbon nanotubes embedded in SiO2. International Journal of Environmental Science and Technology 2016, 13, 1465 -1474.

AMA Style

Sarttrawut Tulaphol, S. Bunsan, E. Kanchanatip, H.-Y. Miao, N. Grisdanurak, W. Den. Influence of chlorine substitution on adsorption of gaseous chlorinated phenolics on multi-walled carbon nanotubes embedded in SiO2. International Journal of Environmental Science and Technology. 2016; 13 (6):1465-1474.

Chicago/Turabian Style

Sarttrawut Tulaphol; S. Bunsan; E. Kanchanatip; H.-Y. Miao; N. Grisdanurak; W. Den. 2016. "Influence of chlorine substitution on adsorption of gaseous chlorinated phenolics on multi-walled carbon nanotubes embedded in SiO2." International Journal of Environmental Science and Technology 13, no. 6: 1465-1474.

Journal article
Published: 01 March 2016 in Chemosphere
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In this study, a multiwalled carbon nanotubes-chitosan (CNTs-CS) composite electrode was fabricated to enable water purification by electrosorption. The CNTs-CS composite electrode was shown to possess excellent capacitive behaviors and good pore accessibility by electrochemical impedance spectroscopy, galvanostatic charge-discharge, and cyclic voltammetry measurements in 1 M H2SO4 electrolyte. Moreover, the CNTs-CS composite electrode showed promising performance for capacitive water desalination. At an electric potential of 1.2 V, the electrosorption capacity and electrosorption rate of NaCl ions on the CNTs-CS composite electrode were determined to be 10.7 mg g(-1) and 0.051 min(-1), respectively, which were considerably higher than those of conventional activated electrodes. The improved electrosorption performance could be ascribed to the existence of mesopores. Additionally, the feasibility of electrosorptive removal of aniline from an aqueous solution has been demonstrated. Upon polarization at 0.6 V, the CNTs-CS composite electrode had a larger electrosorption capacity of 26.4 mg g(-1) and a higher electrosorption rate of 0.006 min(-1) for aniline compared with the open circuit condition. The enhanced adsorption resulted from the improved affinity between aniline and the electrode under electrochemical assistance involving a nonfaradic process. Consequently, the CNT-CS composite electrode, exhibiting typical double-layer capacitor behavior and a sufficient potential range, can be a potential electrode material for application in the electrosorption process.

ACS Style

Chih-Yu Ma; Shih-Ching Huang; Pei-Hsin Chou; Walter Den; Chia-Hung Hou. Application of a multiwalled carbon nanotube-chitosan composite as an electrode in the electrosorption process for water purification. Chemosphere 2016, 146, 113 -120.

AMA Style

Chih-Yu Ma, Shih-Ching Huang, Pei-Hsin Chou, Walter Den, Chia-Hung Hou. Application of a multiwalled carbon nanotube-chitosan composite as an electrode in the electrosorption process for water purification. Chemosphere. 2016; 146 ():113-120.

Chicago/Turabian Style

Chih-Yu Ma; Shih-Ching Huang; Pei-Hsin Chou; Walter Den; Chia-Hung Hou. 2016. "Application of a multiwalled carbon nanotube-chitosan composite as an electrode in the electrosorption process for water purification." Chemosphere 146, no. : 113-120.

Journal article
Published: 01 February 2016 in Journal of Cleaner Production
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ACS Style

Mengshan Lee; Walter Den. Life cycle value analysis for sustainability evaluation of bioenergy products. Journal of Cleaner Production 2016, 113, 541 -547.

AMA Style

Mengshan Lee, Walter Den. Life cycle value analysis for sustainability evaluation of bioenergy products. Journal of Cleaner Production. 2016; 113 ():541-547.

Chicago/Turabian Style

Mengshan Lee; Walter Den. 2016. "Life cycle value analysis for sustainability evaluation of bioenergy products." Journal of Cleaner Production 113, no. : 541-547.

Review
Published: 17 November 2015 in Applied Sciences
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Chitosan, a bio-based polymer which has similar characteristics to those of cellulose, exhibits cationic behavior in acidic solutions and strong affinity for metals ions. Thus, it has received increased attention for the preparation of heterogeneous catalysts. Recent studies demonstrated that chitosan-based catalysts had high sorption capacities, chelating activities, stability and versatility, which could be potentially applied as green reactants in various scientific and engineering applications. This study intends to review the recent development of chitosan-based catalysts, particularly in the aspects of the main mechanisms for preparing the materials and their applications in environmental green chemistry. Studies on the preparation of catalyst nanoparticles/nanospheres supported on chitosan were also reviewed.

ACS Style

Mengshan Lee; Bo-Yen Chen; Walter Den. Chitosan as a Natural Polymer for Heterogeneous Catalysts Support: A Short Review on Its Applications. Applied Sciences 2015, 5, 1272 -1283.

AMA Style

Mengshan Lee, Bo-Yen Chen, Walter Den. Chitosan as a Natural Polymer for Heterogeneous Catalysts Support: A Short Review on Its Applications. Applied Sciences. 2015; 5 (4):1272-1283.

Chicago/Turabian Style

Mengshan Lee; Bo-Yen Chen; Walter Den. 2015. "Chitosan as a Natural Polymer for Heterogeneous Catalysts Support: A Short Review on Its Applications." Applied Sciences 5, no. 4: 1272-1283.