Browsing by Author "Chen, JN"

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A dynamic model of ozone disinfection in a bubble column with oxygen mass transfer
(2002-05-01)
Chen, YH
;
Chang, CY
;
Yu, YH
;
Chiang, PC
;
Chiu, CY
The dynamic process of disinfection with ozone in a bubble column is studied for model establishment. Bubble columns have been widely used for ozone disinfection in plants and laboratories. Ozone is produced by passing oxygen-enriched gas through an ozone generator, and introduced into the bottom of a column equipped with a gas-diffuser. There certainly exists a temporary and unsteady period before the ozone disinfection system reaches steady state. Available ozone disinfection models employed to describe dissolved ozone and surviving microorganism profiles have commonly been developed for steady state. Moreover, oxygen mass transfer has usually been neglected in previous ozone disinfection models. However, this information is desirable for the proper operation of ozone disinfection in a bubble column. Thus, the objective of this study was to model and investigate the dynamic ozone disinfection process in a bubble column with oxygen mass transfer. A dynamic axial dispersion model is proposed and was employed to predict the variation of the ozone, microorganism and oxygen concentrations along the column. The results of prediction were obtained based on the conditions of Marinas et al. (1993). E. coli was chosen as the model microorganism. The dynamic model of ozone inactivation is useful for proper prediction of the variables of an ozone disinfection system in a bubble column.
A project model for software development
(2000-05-01)
Liang, BS
;
Chen, JN
;
Wang, FJ
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
Uncertainty and dynamic changes in a software project cause iterations during development and the need for decision-making in planning and controlling a project. This paper presents a Software Project Review and Evaluation Model, SPREM, a superset of CPM/PERT which extends CPM/PERT's notation to four types of vertices (AA, AX, XA, and XX vertices) to express the non-deterministic and iterative behaviors of software engineering projects. Several behavioral properties of SPREM and analysis of them are discussed. For example, the enaction capability can be used to evaluate the possibility that a vertex will enact processes beforehand. Project managers can revise a SPREM graph to rescue dead vertices before project execution. Furthermore, enaction ordering allows project managers to calculate the dependency between processes to be enacted. This might help in computing important information such as critical paths among these processes.
A refined model for ozone mass transfer in a bubble column
(1998-01-01)
Huang, WH
;
Chang, CY
;
Chiu, CY
;
Lee, SJ
;
Yu, YH
The mathematical model proposed by Marinas et ai. (1993) for a bubble column gas-liquid contactor is refined to described the mass transfer of ozone absorption and decomposition in the aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGb), and the superficial gas rise velocity (u(G)), respectively. The variation of u(G) and the effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of chemical to pure physical mass fluxes according to the film model of gas liquid absorption, are considered in the refined model. This analysis thus extends the applicability of the model of Marinas et al. (1993) and is of special importance for the ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant. An example of such case is the cyanide wastewater treatment in the strong basic condition.
A refined model for ozone mass transfer in a bubble column
(1998-01-01)
Huang, WH
;
Chang, CY
;
Chiu, CY
;
Lee, SJ
;
Yu, YH
The mathematical model proposed by Marinas et ai. (1993) for a bubble column gas-liquid contactor is refined to described the mass transfer of ozone absorption and decomposition in the aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGb), and the superficial gas rise velocity (u(G)), respectively. The variation of u(G) and the effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of chemical to pure physical mass fluxes according to the film model of gas liquid absorption, are considered in the refined model. This analysis thus extends the applicability of the model of Marinas et al. (1993) and is of special importance for the ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant. An example of such case is the cyanide wastewater treatment in the strong basic condition.
A refined model for ozone mass transfer in a semibatch stirred vessel
(1997-11-01)
Chiu, CY
;
Chang, CY
;
Huang, WH
;
Lee, SJ
;
Yu, YH
The mathematical model proposed by Anselmi et al. (1984) for a semibatch stirred gas-liquid contactor is refined to describe the mass transfer of ozone absorption and decomposition in aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGi), and the outlet gas in the free volume above the liquid surface (C-AGe), respectively. The effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of mass absorbed per unit area in time t with chemical reaction (r) to that without chemical reaction or of the purely physical absorption, is considered in the refined model. Furthermore, the refined model also takes into account the variation of E-r with C-ALb, which changes with time during the course of gas-liquid contacting. Thus this analysis extends the applicability of the model of Anselmi et al. (1984) and is of special importance for ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant, and in the system with variable liquid phase ozone concentration.
Adsorption characteristics of dichlorvos onto hydrous titanium dioxide surface
(1996-07-01)
Lu, MC
;
Roam, GD
;
Chen, JN
;
Huang, CP
;
環境工程研究所
Adsorption of dichlorvos (2,2-dichlorovinyl-o,o-dimethl phosphate) onto hydrous TiO2 from water was evaluated in the laboratory using a batch reactor. The presence of organic solvents resulted in a decreasing dichlorvos adsorption on TiO, surface. These data were used to assess a cosolvent model. Decreased adsorption of dichlorvos was observed at an initial pH of 4 with increasing ionic strength. The inhibitory adsorption is attributed to the blockade of surface sites by electrolytes. In addition, electrolytes play an important role on the pa-dependent dichlorvos adsorption. It is suggested that at pH < pH(pzc) (point of zero charge), dichlorvos adsorption is inhibited because electrolytes compete with dichlorvos fbr surface sites. At pH > pH(pzc) the adsorption density of dichlorvos decreases with increasing solution pH due to the decrease of surface group, TiOH, on the TiO2 surface. The variation of adsorption density with temperature over the range 10 degrees-40 degrees C has been investigated. Results show that the reaction is controlled by enthalpy. The adsorption of dichlorvos onto the TiO2 surface is primarily brought about by hydrogen bonding. Copyright (C) 1996 Elsevier Science Ltd
An NMR and XRD study of solidification/stabilization of chromium with portland cement and beta-C2S
(1996-06-01)
Lin, CK
;
Chen, JN
;
Lin, CC
;
環境工程研究所
;
材料科學與工程學系
Solidificalion/stabilization of chromium with Portland cement Type I and P-dicalcium silicate (beta-C2S) was investigated by means of the Si-29 solid stale Magic Angle Spinning/Nuclear Magnetic Resonance (Si-29 MAS/NMR) and X-ray Diffraction (XRD) techniques. It is found that chromium nitrate can increase the extent of beta-C2S hydration. It is also confirmed that the chromium ion is easily incorporated into the beta-C2S paste and hydrated Portland cement, and that it affects the characteristics of hydration and hydration products. Formation of beta-calcium chromium oxide hydrate (beta-CaCrO4 . 2H2(O)) during the hydration of chromium-doped beta-C2S and calcium chromium oxide hydrate (CaCrO4 . 2H(2)O) during the hydration of chromium-doped Portland cement indicates the substitution of chromium for silicon in hydration products. The chromium ion, Cr3+, is thus stabilized and solidified through this mechanism.
An NMR and XRD study of solidification/stabilization of chromium with portland cement and beta-C2S
(1996-06-01)
Lin, CK
;
Chen, JN
;
Lin, CC
;
環境工程研究所
;
材料科學與工程學系
Solidificalion/stabilization of chromium with Portland cement Type I and P-dicalcium silicate (beta-C2S) was investigated by means of the Si-29 solid stale Magic Angle Spinning/Nuclear Magnetic Resonance (Si-29 MAS/NMR) and X-ray Diffraction (XRD) techniques. It is found that chromium nitrate can increase the extent of beta-C2S hydration. It is also confirmed that the chromium ion is easily incorporated into the beta-C2S paste and hydrated Portland cement, and that it affects the characteristics of hydration and hydration products. Formation of beta-calcium chromium oxide hydrate (beta-CaCrO4 . 2H2(O)) during the hydration of chromium-doped beta-C2S and calcium chromium oxide hydrate (CaCrO4 . 2H(2)O) during the hydration of chromium-doped Portland cement indicates the substitution of chromium for silicon in hydration products. The chromium ion, Cr3+, is thus stabilized and solidified through this mechanism.
An NMR, XRD and EDS study of solidification/stabilization of chromium with portland cement and C3S
(1997-09-01)
Lin, CK
;
Chen, JN
;
Lin, CC
;
環境工程研究所
;
材料科學與工程學系
Solidification/stabilization (S/S) of chromium with Portland cement type I and tricalcium silicate (C3S) was investigated by using the Si-29 solid state magic angle spinning/nuclear magnetic resonance (Si-29 MAS/NMR), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The present study confirms that chromium nitrate can increase the extent of C3S hydration. It also confirms that the chromium ion is easily incorporated into the C3S paste and hydrated Portland cement, and that it affects the characteristics of the hydration processes and their hydration products, The formation of calcium chromium silicate (CaCrSi4O10), calcium chromium oxide hydrate (CaCrO4 . 2H(2)O), and calcium dichromate (CaCr2O7) during the hydration of chromium-doped C3S indicates the probable substitution of chromium for silicon in the calcium silicate hydrate (C-S-H) and the interaction between Cr and Si. Furthermore, formation of CaCrSi4O10, aluminum chromium oxide hydroxide hydrate (Al(OH)CrO4 . H2O), aluminum chromium oxide hydroxide (Al-2(OH)(4)CrO4), and CaCr2O7 during the hydration of chromium-doped cement reveals not only the probable substitution of chromium for silicon in the calcium silicate hydrate (C-S-H) but also the interaction among Cr, Si and Al, Apparently, the chromium iron (Cr3+) may also be stabilized and solidified through these mechanisms in addition to those proposed by other investigators. (C) 1997 Elsevier Science B.V.
Application of a membrane bioreactor system for opto-electronic industrial wastewater treatment - a pilot study
(2003)
Chen, TK
;
Chen, JN
;
Ni, CH
;
Lin, GT
;
Chang, CY
The membrane bioreactor (MBR) system has become more and more attractive in the field of wastewater treatment. It is particularly attractive in situations where long solids retention times are required, such as nitrifying bacteria, and physical retention is critical to achieving more efficiency for biological degradation of pollutants. Although it is a new technology, the MBR process has been applied to industrial wastewater treatment for only the past decade. The opto-electronic industry, developed very fast over the past decade in the world, is a high technological manufacturing industry. The treatment of the opto-electronic industrial wastewater containing a significant quantity of organic nitrogen compounds, with a ratio over 95% in organic nitrogen (Org-N) to total nitrogen (T-N), is very difficult to meet the discharge limits. The purpose of this research is mainly to discuss the treatment capacity of high-strength organic nitrogen wastewater, and to investigate the capabilities of the MBR process. A 2 m(3)/day capacity MBR pilot plant consisting of anoxic and aerobic tanks and a membrane bioreactor was installed for evaluation. The operation was continued for 130 days. Over the whole experimental period, a satisfactory organic removal performance was achieved. The COD could be removed with an average of over 94.5%. For TOC and BOD5, the average removal efficiencies were 96.3 and 97.6%, respectively. The nitrification and denitrification were also successfully achieved. The effluent did not contain any suspended solids. Only a small concentration of ammonia nitrogen was found in the effluent. The stable effluent quality and satisfactory removal performance mentioned above were ensured by the efficient interception performance of the membrane device incorporated within the biological reactor. The MBR system shows promise as a means of treating very high organic nitrogen wastewater without dilution. The effluent of TKN, NOx-N and COD can fall below 20 mg/L, 30 mg/L and 50 mg/L.
Catalytic decomposition of hydrogen peroxide and 2-chlorophenol with iron oxides
(2001-06-01)
Huang, HH
;
Lu, MC
;
Chen, JN
;
環境工程研究所
;
Institute of Environmental Engineering
The aim of this study was to examine the catalyzed decomposition of hydrogen peroxide and 2-chlorophenol (2-CP) in the presence of iron oxides. C;ranular ferrihydrite, goethite, and hematite were selected as catalysts in this study. 2-CP was used as the model compound because it is a typical toxic compound and has not been investigated in the catalytic decomposition by iron oxides. The catalytic activity for hydrogen peroxide decomposition followed the sequence: granular ferrihydrite > goethite > hematite. However, hematite exhibited the highest activity in catalyzing 2-CP oxidation. The oxidation efficiency of 2-CP corresponded with the inverse sequence of specific area and pH,,, of the iron oxides. The catalytic activity of granular ferrihydrite was affected significantly by the mixing speed and particle size for its large value of Thiele modulus (phi) and Damkohler number (Da). The strong diffusion resistance for granular ferrihydrite was attributed either to its microporous structure or to the formation of oxygen in the pores of the iron oxide leading to the unexpected catalytic activity of granular ferrihydrite to hydrogen peroxide and 2-CP. (C) 2001 Elsevier Science Ltd. All rights reserved.
Catalytic decomposition of hydrogen peroxide and 4-chlorophenol in the presence of modified activated carbons
(2003-06-01)
Huang, HH
;
Lu, MC
;
Chen, JN
;
Lee, CT
;
環境工程研究所
The objective of this research was to examine the heterogeneous catalytic decomposition of H2O2 and 4-chlorophenol (4-CP) in the presence of activated carbons modified with chemical pretreatments. The decomposition of H2O2 was suppressed significantly by-the change of surface properties including the decreased pH(pzc) modified with oxidizing agent and the reduced active sites occupied by the adsorption of 4-CP. The apparent reaction rate of H2O2 decomposition was dominated by the intrinsic reaction rates on the surface of activated carbon rather than the mass transfer rate of H2O2 to the solid surface. By the detection of chloride ion in suspension, the reduction of 4-CP was not only attributed to the advanced adsorption but also the degradation of 4-CP. The catalytic activity toward 4-CP for the activated carbon followed the inverse sequence of the activity toward H2O2, suggesting that acidic surface functional group could retard the H2O2 loss and reduce the effect of surface scavenging resulting in the increase of the 4-CP degradation efficiency. Few effective radicals were expected to react with 4-CP for the strong effect of surface scavenging, which could explain why the degradation rate of 4-CP observed in this study was so slow and the dechlorination efficiency was independent of the 4-CP concentration in aqueous phase. Results show that the combination of H2O2 and granular activated carbon (GAC) did increase the total removal of 4-CP than that by single GAC adsorption. (C) 2003 Elsevier Science Ltd. All rights reserved.
Catalytic decomposition of ozone in the presence of water vapor
(1998)
Tsai, WT
;
Chang, CY
;
Jung, FH
;
Chiu, CY
;
Huang, WH
The catalytic decomposition of ozone in the presence of water vapor at the relative humidity (RH) of about 90 % was investigated by using a tubular fixed-bed reactor. The performance tests and reaction kinetic studies were conducted for catalyst, i.e., Pt/gamma-Al2O3 (symbolized as Dash-220). The experiments were carried out at various constant reaction temperatures (298 similar to 323 K) and space velocities (24,000 similar to 44,000 hr(-1)). About 75 % decomposition efficiencies of ozone with inlet concentration of about 0.17 mol/m(3) was achieved at catalyst contact time of 015 sec (space velocity of 24,000 hr(-1)), reaction temperature of 323 K and RH of about 90 % for the Dash-220 catalyst. However, about 97 % decomposition efficiencies of ozone without the presence of water vapor at the same reaction conditions. The results indicated that the Dash-220 catalyst with the presence of water vapor gave lower performance of ozone decomposition than without the presence of water vapor can be achieved at the same reaction conditions. For the reaction kinetics, it was found that the pseudo-first-order chemical reaction rate equation was appropriate for the catalytic decomposition of ozone in the presence of water vapor investigated in this study. The apparent activation energies for the decomposition reaction of ozone using the Dash-220 catalyst in the presence of water vapor at RH of 90 % is 19.32 kJ mol(-1). The corresponding pre-exponential factor is 0.0041 mol/(s g-catalyst (mol/m(3))).
Catalytic ozonation of 2-dichlorophenol by metallic ions
(2003)
Ni, CH
;
Chen, JN
;
Yang, PY
;
環境工程研究所
;
Institute of Environmental Engineering
This research is mainly to explore functional improvement by adding various kinds of metallic ions in the ozonation of 2-chlorophenol solution. During the experiment, various kinds of metallic ions (Pb+, Cu2+, Zn2+, Fe2+, Ti2+, and Mn2+) were added; it was found that the reaction rate increased in all cases. The best result was obtained by using manganese ions, followed by iron and titanium ions. At pH = 3 and 1 ppm Mn2+ concentration, the reaction rate was increased by three times. TOC removal rate was also increased from 12.6% to 38% at 60 min reaction time. Ozone self-decomposition with various kinds of metallic ions alone was tested. It was found the ozone self-decomposition coefficient is highly dependent on the reaction rate constant for ozonation of 2-chlorophenol. The improvement of reaction was relevant to the mechanism of reaction between ozone and metallic ions. Furthermore, the effect of adding manganese ions was studied. With the initial manganese concentration at 0-2 ppm, after gas exposure for 20 min the removal rate can be increased from 38% to 93%. TOC removal rate was increased from 11% to 38%. The reaction rate was improved more greatly at the initial pH = 3.
Characteristics of photocatalytic oxidation of gaseous 2-propanol using thin-film TiO2 photocatalyst
(2004-11-01)
Chang, CP
;
Chen, JN
;
Lu, MC
;
環境工程研究所
;
Institute of Environmental Engineering
This work presents a photocatalysis-based method to treat and purify air because of its broad applicability to common, oxidizable, air contaminants. The effect of oxygen content, temperature, water vapor, and 2-propanol concentration on the TiO2 surface was investigated. The rate of 2-propanol decomposition increased with increasing the oxygen content, but was reduced at temperatures higher than 100degreesC. When water vapor concentration was in the range of 10-355 mmol m(-3), the rate of 2-propanol decomposition was proportional to the water content. However, an opposite result was observed at a higher concentration of water vapor. 2-Propanol was photooxidized to acetone, and eventually to carbon dioxide and water. The kinetic model of 2-propanol photooxidation was successfully developed by the competitive Langmuir-Hinshelwood rate form, incorporating the inhibition effect coming from the formation of acetone. (C) 2004 Society of Chemical Industry.
Combined absorption and self-decomposition of ozone in aqueous solutions with interfacial resistance
(1996-05-01)
Chang, CY
;
Chiu, CY
;
Lee, SJ
;
Huang, WH
;
Yu, YH
A theoretical analysis is performed employing the film model for the isothermal absorption and self-decomposition of ozone in aqueous solutions with interfacial resistance, which is inversely proportional to the interfacial mass transfer coefficient k(g). A closed-form solution has been obtained. The effects of system parameters on the ozone mass transfer rate are examined. These parameters include the interfacial resistance (1/k(g)),the acidic and basic self-decomposition reaction rate parameters (M(m)(0.5), M(n)(0.5); M(m) = [2D(A)k(m)C(Ai)(m-1)/((m+1)]/k(L)(0))(2), M(n) = (2D(A)k(n)C(Ai)(n-1)/(n+1))/k(L)(0))(2), the reaction orders (m,n), the pH value of solution, and the liquid-phase mass transfer coefficient (k(L)(0)). The results indicate that the reduction effect of the interfacial resistance on the absorption rate is most significant for the situation with the larger values of M(m) and M(n) as well as with higher pH values. Also, for any particular finite value of k(L)(0)/k(g), the reduction effect encountered is greater for a gas liquid contactor with a lower k(L)(0). The reduction effect should be avoided in order to maintain a higher mass transfer rate of ozone in aqueous solution. This analysis is of importance for the efficient use of ozone in water/wastewater treatment processes in the presence of interfacial resistance substances such as surface active agents. For some known special cases (for example, cases with no interfacial resistance), the present solution reduces to the previous works of other investigators.
Combined membrane bioreactor (MBR) and reverse osmosis (RO) system for thin-film transistor - liquid crystal display TFT-LCD, industrial wastewater recycling
(2004)
Chen, TK
;
Chen, JN
;
環境工程研究所
;
Institute of Environmental Engineering
In TFT-LCD industry, water plays a variety of roles as a cleaning agent and reaction solvent. As good quality water is increasingly a scarce resource and wastewater treatment costs rises, the once-through use of industrial water is becoming uneconomical and environmentally unacceptable. Instead, recycling of TFT-LCD industrial wastewater is become more attractive from both an economic and environmental perspective. This research is mainly to explore the capacity of TFT-LCD industrial wastewater recycling by the process combined with membrane bioreactor and reverse osmosis processes. Over the whole experimental period, the MBR process achieved a satisfactory organic removal. The COD could be re,moved with an average of over 97.3%. For TOC and BOD5 items, the average removal efficiencies were 97.8 and 99.4% respectively. The stable effluent quality and satisfactory removal performance were ensured by the efficient interception performance of the UF membrane device incorporated with biological reactor. Moreover, the MBR effluent did not contain any suspended solids and the SDI value was under 3. Aftr treatment of RO, excellent water quality of permeate were under 5 mg/l, 2.5 mg/l and 150 mus/cm for COD, TOC and conductivity respectively. The treated water can be recycled for the cooling tower make-up water or other purposes.
Decomposition of 2-mercaptothiazoline in aqueous solution by ozonation
(2004-07-01)
Chen, YH
;
Chang, CY
;
Chen, CC
;
Chiu, CY
;
Yu, YH
This study investigates the ozonation of 2-mercaptothiazoline (2-MT). The 2-MT is one of the important organic additives for the electroplating solution of the printed wiring board industry and has been widely used as a corrosion inhibitor in many industrial processes. It is of concern for the aquatic pollution control especially in the wastewaters. Semibatch ozonation experiments in the completely stirred tank reactor are performed under various concentrations of input ozone. The concentrations of 2-MT, sulfate, and ammonium are analyzed at specified time intervals to elucidate the decomposition of 2-MT during the ozonation. In addition, the time variation of the dissolved ozone concentration (C-ALb) is continuously monitored in the course of experiments. Total organic carbon (TOC) is chosen and measured as a mineralization index of the ozonation of 2-MT. The results indicate that the decomposition of 2-MT is efficient, while the mineralization of TOC is limited via the ozonation only. Simultaneously, the yield of sulfate with the maximum value of about 47% is characterized by the increases of TOC removal and ozone consumption. These results can provide some useful information for assessing the feasibility of the treatment of 2-MT in the aqueous solution by the ozonation. (C) 2004 Elsevier Ltd. All rights reserved.
Decomposition of 2-naphthalenesulfonate in aqueous solution by ozonation with UV radiation
(2002-09-01)
Chen, YH
;
Chang, CY
;
Huang, SF
;
Chiu, CY
;
Ji, D
This study investigates the ozonation of 2-naphthalenesulfonate (2-NS) combined With ultraviolet (UV) radiation, Naphthalenesulfonic acids are of importance as dye intermediates for the dye and textile auxiliary industries. Its derivatives, such as 2-NS. have been found in rivers and tannery effluents causing Pollution problems. Thus, the 2-NS is of concern for the aquatic pollution control especially in the surface and waste waters. Ozonation combined with UV radiation is employed for the removal of 2-NS in the aqueous solution. Semibatch ozonation experiments were proceeded under different reaction conditions to studs the effects of ozone dosage and UV radiation on the oxidation of 2-NS. The concentrations of 2-NS and sulfate are analyzed at specified time internals to elucidate the decomposition of 2-NS. In addition, values of pH and oxidation reduction potential are continuously Measured in the course of experiments. Total organic carbon is chosen as a mineralization index of the ozonation of 2-NS, The mineralization of 2-NS via the ozonation is remarkably enhanced by the UV radiation. These results can provide useful information for the proper removal of 2-NS in the aqueous solution by the ozonation with UV radiation. (C) 2002 Published by Elsevier Science Ltd.
Dynamic behavior of ozonation with pollutant in a countercurrent bubble column with oxygen mass transfer
(2003-06-01)
Chen, YH
;
Chang, CY
;
Chiu, CY
;
Yu, YH
;
Chiang, PC
The dynamic behavior of ozonation with pollutants in a countercurrent bubble column is studied for the model establishment. Bubble columns have been widely used for an ozonation system in the plants and laboratories. In addition, a countercurrent bubble column has been commonly recommended than a cocurrent one because it has a higher ozone transfer efficiency. Therefore, the investigation of this paper focuses on the countercurrent bubble column. As an ozonation process starts, the gas mixture of ozone and oxygen is introduced into the bottom of a column, and then transferred into the liquid. The pollutants in the wastewater are eliminated subsequently via oxidation by the dissolved ozone. There certainly exists a temporary and unsteady period before the ozonation system reaches steady state. However, available ozonation models employed to describe ozone and pollutant profiles have commonly been developed for steady state. The treating qualities of wastewater in the early stage of ozonation are usually not predicted, and the time required for the steady-state establishment remains to be determined. Moreover, oxygen mass transfer is usually neglected in previous ozonation models so that the increase of dissolved oxygen is uncertain. These information is desirable for the proper design and operation of ozonation system in a bubble column. Thus, the aim of this study is to model and investigate the dynamic processes of ozonation with pollutants including oxygen mass transfer. The dynamic axial dispersion model proposed is employed to predict the variation of the ozone, pollutant, and oxygen concentrations profiles. The validity of the model was demonstrated by comparing the predicted results with the experimental data. The o-cresol was chosen as the model pollutant. The temporal concentration variations of the residual o-cresol and dissolved oxygen in the effluent liquid, and the off-gas ozone in the free volume were measured accordingly. Furthermore, the variation of the enhancement factor of ozone and the amount of off-gas were predicted. Note that it usually needs 2-5 hydraulic retention times to approach steady state under the conditions of this study. Further, the effects of dimensionless system parameters on the performance of the ozonation processes are examined. As a result, the proposed dynamic model of ozonation with pollutants is useful for proper prediction of the variables of an ozonation system in a countercurrent bubble column. (C) 2003 Elsevier Science Ltd. All rights reserved.