Browsing by Author "Den, W"

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Biotrickling filtration for control of volatile organic compounds from microelectronics industry
(2003-07-01)
Den, W
;
Huang, CP
;
Li, CH
;
環境工程研究所
;
生物科技學系
This study investigated the transient and steady-state performance of a bench-scale biotrickling filter for the removal of an organic mixture (acetone, toluene, and trichloroethylene) typically emitted by the microelectronics industry. The, microbial consortium consisting of seven bacterial strains that were fully acclimated prior to inoculation onto activated carbon media. Among the seven strains, the Pseudomonas and Sphingomonas strains appeared to be the major groups degrading toluene (> 25 ppmv/h (.) 10(8) cell) and trichloroethylene (>2.3 ppmv/h. 10(8.) cell), while Mycobacteria and Acetobacteriaceae strains were the primary decomposers of acetone (> 90 ppmv/h (.) 10(8) cell). The column performance was evaluated by examining its responses to the fluctuating influent total hydrocarbon concentrations, which varied from 850 to 2,400 ppmv. Excellent steady-state removal efficiencies greater than 95% were consistently observed, and system recovery was typically within two days after a significant increase,in the inlet loading was experienced. The overall mass-transfer rate and the biokinetic constants were determined for each organic component. Mathematical simulations based on these parameters demonstrated that the removal of acetone was kinetically limiting, whereas the removals of toluene and trichloroethylene were. at least partially mass-transfer limiting.
Direct quantitative analysis of phthalate esters as micro-contaminants in cleanroom air and wafer surfaces by auto-thermal desorption-gas chromatography-mass spectrometry
(2005-04-08)
Kang, YH
;
Den, W
;
Bai, HL
;
Ko, FH
;
環境工程研究所
This study established an analytical method for the trace analyses of two phthalate esters, including diethyl phthalate (DEP) and di-n-butyl phthalate (DBP), known as the major constituents of cleanroom micro-contamination detrimental to the reliability of semiconductor devices. Using thermal desorption coupled with a GC-MS system, standard tubes were prepared by delivering liquid standards pre-vaporized by a quasi-vaporizer into Tenax GR tubes for calibration. This method was capable of achieving detection limits of 0.05 mu g m(-3) for 0.1 m(3) air samples and 0.03 ng cm(-2) for 150-mm wafer surface density. Actual samples collected from a semiconductor cleanroom showed that the concentration of DBP in a polypropylene wafer box (0.45 mu g m(-3)) was nearly four times higher than that in the cleanroom environment (0.12 mu g m(-3)). The surface contamination of DBP was 0.67 ng cm(-2) for a wafer stored in the wafer box for 24 h. Furthermore, among the three types of heat-resistant O-ring materials tested, Kalrez((R)) was found to be particularly suitable for high-temperature processes in semiconductor cleanrooms due to their low emissions of organic vapors. This analytical procedure should serve as an effective monitoring method for the organic micro-contamination in cleanroom environments. (c) 2005 Elsevier B.V. All rights reserved.
Effects of cross-substrate interaction on biotrickling filtration for the control of VOC emissions
(2004-11-01)
Den, W
;
Huang, CP
;
Li, CH
;
環境工程研究所
;
生物科技學系
The effects of cross-substrate interaction to the performance of a gas-phase biotrickling filter for treating a mixture of volatile organic compounds (VOCs), including three structural heterologous in acetone, toluene, and trichloroethylene, were investigated. The biotrickling filter was inoculated with microbial consortium containing at least seven bacterial species utilizing either acetone or toluene, or both, as their carbon sources. In the performance study, the column operating under variable conditions typifying the waste gas emission from the microelectronics fabrication processes achieved a total hydrocarbon (THC) removal efficiency in excess of 85% and a mineralization capacity over 50% for THC mass loading as high as 36.2 g-CH4 m(-3) h(-1). The cross-substrate effects were examined by correlating the relative changes in the mass removal of each substrate with the biodegradative capability of the microbial consortium. The degradation of trichloroethylene was primarily due to co-metabolism by the toluene-oxidizing enzymes, but the results also indicated that trichloroethylene partially induced its own degradation. Concentration increases in acetone appeared to cause a diauxie effect that suppressed degradation of toluene and trichloroethylene, and shifted the microbial population toward the selective acetone-degraders. No irrecoverable toxicity or inhibitory effects were observed throughout the experiments. These results suggest that the relative VOC concentration in the waste gas mixture is a factor as important as the biodegradative function of the microbial consortium, and thus should be carefully evaluated to satisfy the treatment objectives. (C) 2004 Elsevier Ltd. All rights reserved.
Electrocoagulation for removal of silica nano-particles from chemical-mechanical-planarization wastewater
(2005-03-10)
Den, W
;
Huang, CP
;
環境工程研究所
;
Institute of Environmental Engineering
Continuous-flow electrocoagulation process with vertical flow-channels was investigated as a method to treat synthetic chemical-mechanical-planarization (CMP) wastewater containing highly charged ultrafine silica particles (zeta = -55 mV, mean R-p = 45 nm at pH 9.5). The parallel-plate, monopolar electrochemical cells resembled a series of closed electrical circuits such that the electrical field strength was highly dependent of the current density and aqueous conductivity, but independent of the inter-electrode gap. The residual turbidity of the CMP wastewater decreased with the increases in either hydraulic retention time or applied current density, and removal efficiency as high as 95% was achieved for wastewater with both low (70NTU) and high (400 NTU) initial turbidities. The charge loading linearly correlated with turbidity removal efficiency up to a level of 8 F m(-3), presenting an appropriate design parameter. Further analysis indicated that turbidity removal was limited by the quantity of liberated ferrous ions at lower range of current density, but seemingly reached a critical level of current density beyond which the process performance gradually deteriorated. Comparisons between the effective particle retention time and the estimated electrophoretic migration time revealed that the electrocoagulation process was predominantly controlled by the rate of particle aggregation occurring near the anodic surfaces. Furthermore, this process generates lesser amount of dry sludge as compared to chemical coagulation with polyaluminum chloride, and does not require pH adjustment prior to treatment. (C) 2004 Elsevier B.V.. All rights reserved.
Mechanistic study on the continuous flow electrocoagulation of silica nanoparticles from polishing wastewater
(2006-05-10)
Den, W
;
Huang, CP
;
Ke, HC
;
環境工程研究所
;
Institute of Environmental Engineering
This study investigates the removal mechanisms involved in the monopolar, continuous-flow electrocoagulation of a polishing wastewater containing negatively charged silica particles. Using iron as the anodes, the mechanisms were inferred from the experimental observations of the changes in pH, zeta-potential, and turbidity as a function of reaction time, as well as from the sludge characterization. Two types of distinct mechanisms were observed, one involving particle destabilization by oppositely charged ferrous ions and the other involving coprecipitation or enmeshment of silica particles with the iron hydroxides. The former mechanism was apparently responsible for the formation of "surface flocs", whereas the latter one was responsible for the "sediment sludge". The sludge collected separately from the two "sinks" was distinctly different in both physical appearance and settling velocity. Furthermore, based on the sheer quantity of the surface flocs and the sediment sludge, the two mechanisms involved in the electrocoagulation process were equally important to the silica removal.
Monodisperse nanoparticle synthesis by an atmospheric pressure plasma process: An example of a visible light photocatalyst
(2004-10-27)
Bai, HL
;
Chen, CC
;
Lin, CS
;
Den, W
;
Chang, CL
An atmospheric pressure plasma-enhanced nanoparticle synthesis (APPENS) process was proposed to produce a titania-based visible light photocatalyst. The titanium tetraisopropoxide (TTIP) precursor was vaporized with a N-2 carrier gas and entered a nonthermal AC plasma system. The N-2 gas was dissociated into N atoms by the plasma energy, and then they were doped into the precursor vapors. The produced TiO2-xNx nanoparticles were highly uniform and adjustable in size. The titania-based particle sizes ranged from 25 to 40 nm, and they depended on the precursor ratio of TTIP/H-2O. In addition to producing the photocatalytic particles, the APPENS process has a potential application as a continuous-flow nanosize monodisperse aerosol generator.
Organic airborne molecular contamination in semiconductor fabrication clean rooms - A review
(2006)
Den, W
;
Bai, HL
;
Kang, YH
;
環境工程研究所
;
Institute of Environmental Engineering
Monitoring of airborne molecular contamination (AMC) has become a crucial element of cleanroom management as the production phase of semiconductor devices marches deep into sub-100-nm range. The current understandings of the AMC, particularly those with organic origins, are presented comprehensively in this article based on the research reports within the past ten years. Starting with a review of the chronological development of AMC problems and several approaches for the AMC classifications, this article also examines the merits of several available ambient sampling and surface analytical methods. The focal point of the article is to address the surface deposition potential of organic AMCs by experimentally correlating the surface speciation and abundance of the organic AMCs with their physical and chemical characteristics, together with the kinetic models delineating the rates of deposition for both single-and multiple-contaminant scenarios. In addition, the current progress of the AMC control strategies, especially the development of the chemical filtration technology, is also examined in the paper. (c) 2006 The Electrochemical Society.
Parameter optimization and design aspect for electrocoagulation of silica nano-particles in wafer polishing wastewater
(2006)
Den, W
;
Huang, C
;
環境工程研究所
;
Institute of Environmental Engineering
A systematic procedure has been proposed for the design of a multi-channel, continuous-flow electrocoagulation reactor of mono-polar configuration for the removal of sub-micron particles from wastewater. Using the chemical-mechanical-planarization (CMP) process as the target source of wastewater, a series of laboratory-scale studies were conducted to determine the required operating conditions for the efficient removal of the ultrafine particles. These operating criteria included charge loading ( >= 8 F m(-3)), current density ( >= 5.7 A m(-2)), hydraulic retention time ( >= 60 min), as well as the initially operational pH (7 similar to 10). Furthermore, a steady-state transport equation with second-order reaction kinetics was employed to describe the rate of coagulation as the rate-limiting factor, The actual kinetic constant determined from the laboratory-scale experiments was approximately 1.2 x 10(-21) m(3) s(-1), which was three orders of magnitude smaller than that calculated based on Brownian diffusion during the coagulation. The model was subsequently validated with a series of experiments using a pilot-scale electro-coagulation reactor geometrically similar to the laboratory-scale reactor with nearly twenty times volumetric scale-up.
Short time deposition kinetics of diethyl phthalate and dibutyl phthalate on a silicon wafer surface
(2006-02-15)
Kang, YH
;
Den, W
;
Bai, HL
;
環境工程研究所
;
Institute of Environmental Engineering
Short time adsorption and desorption behaviors of two alkyl phthalate esters, namely diethyl phthalate (DEP) and dibutyl phthalate (DBP), on silicon wafers exposed under various ambient concentrations were experimentally and theoretically investigated. The results showed that the surface density of DBP was significantly affected by both the length of exposure time and its ambient concentration, whereas that of DEP was only affected by its ambient concentration within the tested periods between 60 and 240 min. The determination of rate parameters for adsorption and desorption showed that the rate constants of DEP were always larger than those of DBP. Also, the sticking coefficient of DEP was larger during the initial adsorption stage due to its relatively lower molecular weight as compared to DBP. The value of the sticking coefficient for DEP, however, decreased much faster such that the value eventually became smaller than that for DBP. Therefore, for silicon wafers experiencing a short exposure time, organic compounds with lower molecular weights may be a more important source of airborne molecular contamination than those with higher molecular weights.