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ABSTRACT: The objectives of this bench-scale study were to (1) determine the optimal operational parameters and kinetics when potassium permanganate (KMnO4) was applied to in situ oxidize and remediate trichloroethylene (TCE)-contaminated groundwater and (2) evaluate the effects of manganese dioxide (MnO2) on the efficiency of TCE oxidation. The major controlling factors in the TCE oxidation experiments included molar ratios of KMnO4 to TCE (P value) and molar ratios of Na2HPO4 to Mn2+ (D value). Results show that the second-order decay model can be used to describe the oxidation when P value was less than 20, and the observed TCE decay rate was 0.8M(-1)s(-1). Results also reveal that (1) higher P value corresponded with higher TCE oxidation rate under the same initial TCE concentration condition and (2) higher TCE concentration corresponded with higher TCE oxidation rate under the same P value condition. Results reveal that significant MnO2 production and inhibition of TCE oxidation were not observed under acidic (pH 2.1) or slightly acidic conditions (pH 6.3). However, significant reduction of KMnO(4) to MnO2 would occur under alkaline condition (pH 12.5), and this caused the decrease in TCE oxidation rate. Results from the MnO2 production experiments show that MnO2 was produced from three major routes: (1) oxidation of TCE by KMnO4, (2) further oxidation of Mn2+, which was produced during the oxidation of TCE by KMnO4, and (3) reduction of MnO4(-1) to MnO2 under alkaline conditions. Up to 81.5% of MnO2 production can be effectively inhibited with the addition of Na2HPO4. Moreover, the addition of Na2HPO4 would not decrease the TCE oxidation rate.
Journal of Hazardous Materials 06/2008; 153(3):919-27. · 4.17 Impact Factor
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ABSTRACT: The main objective of this study was to examine the efficacy and capacity of using constructed wetlands on industrial pollutant removal. Four parallel pilot-scale modified free water surface (FWS) constructed wetland systems [dimension for each system: 4-m (L)x1-m (W)x1-m (D)] were installed inside an industrial park for conducting the proposed treatability study. The averaged influent contains approximately 170 mg l(-1) chemical oxygen demand (COD), 80 mg l(-1) biochemical oxygen demand (BOD), 90 mg l(-1) suspend solid (SS), and 32 mg l(-1) NH(3)-N. In the plant-selection study, four different wetland plant species including floating plants [Pistia stratiotes L. (P. stratiotes) and Ipomoea aquatica (I. aquatica)] and emergent plants [Phragmites communis L. (P. communis) and Typha orientalis Presl. (T. orientalis)] were evaluated. Results show that only the emergent plant (P. communis) could survive and reproduce with a continuous feed of 0.4m(3)d(-1) of the raw wastewater. Thus, P. communis was used in the subsequent treatment study. Two different control parameters including hydraulic retention time (HRT) (3, 5, and 7d) and media [vesicles ceramic bioballs and small gravels, 1cm in diameter] were examined in the treatment study. Results indicate that the system with a 5-d HRT (feed rate of 0.4m(3)d(-1)) and vesicles ceramic bioballs as the media had the acceptable and optimal pollutant removal efficiency. If operated under conditions of the above parameters, the pilot-plant wetland system can achieve removal of 61% COD, 89% BOD, 81% SS, 35% TP, and 56% NH(3)-N. The treated wastewater meets the current industrial wastewater discharge standards in Taiwan.
Chemosphere 07/2006; 64(3):497-502. · 3.21 Impact Factor
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ABSTRACT: An oil-refining plant site located in southern Taiwan has been identified as a petroleum-hydrocarbon [mainly methyl tert-butyl ether (MTBE) and benzene, toluene, ethylbenzene, and xylenes (BTEX)] spill site. In this study, groundwater samples collected from the site were analyzed to assess the occurrence of intrinsic MTBE biodegradation. Microcosm experiments were conducted to evaluate the feasibility of biodegrading MTBE by indigenous microorganisms under aerobic, cometabolic, iron reducing, and methanogenic conditions. Results from the field investigation and microbial enumeration indicate that the intrinsic biodegradation of MTBE and BTEX is occurring and causing the decrease in MTBE and BTEX concentrations. Microcosm results show that the indigenous microorganisms were able to biodegrade MTBE under aerobic conditions using MTBE as the sole primary substrate. The detected biodegradation byproduct, tri-butyl alcohol (TBA), can also be biodegraded by the indigenous microorganisms. In addition, microcosms with site groundwater as the medium solution show higher MTBE biodegradation rate. This indicates that the site groundwater might contain some trace minerals or organics, which could enhance the MTBE biodegradation. Results show that the addition of BTEX at low levels could also enhance the MTBE removal. No MTBE removal was detected in iron reducing and methanogenic microcosms. This might be due to the effects of low dissolved oxygen (approximately 0.3mg/L) within the plume. The low iron reducers and methanogens (<1.8103cell/g of soil) observed in the aquifer also indicate that the iron reduction and methanogenesis are not the dominant biodegradation patterns in the contaminant plume. Results from the microcosm study reveal that preliminary laboratory study is required to determine the appropriate substrates and oxidation-reduction conditions to enhance the biodegradation of MTBE. Results suggest that in situ or on-site aerobic bioremediation using indigenous microorganisms would be a feasible technology to clean up this MTBE-contaminated site.
Environmental Geology 05/2006; 50(3):439-445. · 1.13 Impact Factor
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ABSTRACT: Contamination of groundwater by petroleum-hydrocarbons is a serious environmental problem. The Monitored Natural Attenuation (MNA) approach is a passive remediation to degrade and dissipate groundwater contaminants in situ. In this study, a full-scale natural bioremediation investigation was conducted at a gasoline spill site. Results show that concentrations of major contaminants (benzene, toluene, ethylbenzene, and xylenes) dropped to below detection limit before they reached the downgradient monitor well located 280 m from the spill location. The results also reveal that natural biodegradation was the major cause of the observed contaminant reduction. The calculated natural first-order attenuation rates for BTEX and 1,2,4-trimethylbenzene (1,2,4-TMB) ranged from 0.051 (benzene) to 0.189 1/day (1,2,4-TMB). Evidence for the occurrence of natural attenuation includes the following: (1) depletion of dissolved oxygen, nitrate, and sulfate; (2) production of dissolved ferrous iron, sulfide, and CO2; (3) decreased BTEX concentrations and BTEX as carbon to TOC ratio along the transport path; (4) increased alkalinity and microbial populations; (5) limited spreading of the BTEX plume; and (6) preferential removal of certain BTEX components along the transport path. Additionally, the biodegradation capacity (44.73 mg/L) for BTEX and 1,2,4-TMB was much higher than other detected contaminants within the plume. Hence, natural attenuation can effectively contain the plume, and biodegradation processes played an important role in contaminant removal.
Water Science & Technology 02/2006; 53(2):321-8. · 1.12 Impact Factor
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ABSTRACT: Recently, the appearance of assimilable organic carbon (AOC) in the water treatment system and effluent of the treatment plant has brought more attention to the environmental engineers. In this study, AOC removal efficiency at the Cheng-Ching Lake water treatment plant (CCLWTP) was evaluated. The main objectives of this study were to: (1) evaluate the treatability of AOC by the advanced treatment system at the CCLWTP, (2) assess the relativity of AOC and the variations of other water quality indicators, (3) evaluate the effects of sodium thiosulfate on AOC analysis, and (4) evaluate the efficiency of biofiltration process using granular activated carbon (GAC) and anthracite as the fillers. Results show that the averaged influent and final effluent AOC concentrations at the CCLWTP were approximately 124 and 30 µg acetate-C/L, respectively. Thus, the treatment plant had an AOC removal efficiency of about 76%, and the AOC concentrations in the final effluent met the criteria established by the CCLWTP (50 µg acetate-C/L). Results indicate that the biofiltration process might contribute to the removal of the trace AOC in the GAC filtration process. Moreover, the removal of AOC had a correlation with the decrease in concentrations of other drinking water indicators. Results from a column test show that GAC was a more appropriate material than anthracite for the AOC removal. Results from this study provide us insight into the mechanisms of AOC removal by advanced water treatment processes. These findings would be helpful in designing a modified water treatment system for AOC removal and water quality improvement.
Desalination. 01/2006; 202:318-325.
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ABSTRACT: Methyl tert-butyl ether (MTBE) has been used as a gasoline additive to improve the combustion efficiency and to replace lead since 1978. Because it is widely used and it has been disposed inappropriately, MTBE has become a prevalent groundwater contaminant worldwide. In this study, two petroleum-hydrocarbon contaminated sites (Sites A and B) were selected to evaluate the occurrence and effectiveness of natural attenuation of MTBE at these two sites. Field investigation results indicate that the natural attenuation mechanisms of MTBE at both sites were occurring with the first-order attenuation rates of 0.0021 and 0.0048 1day(-1) at Sites A and B, respectively. Results also reveal that the intrinsic biodegradation pattern was the most important mechanism among the natural attenuation processes at both sites. Results from BIOSCREEN simulation suggest that biodegradation was responsible for 78 and 59% of MTBE mass reduction at Sites A and B, respectively. Investigation results show that MTBE plume at Site B could be effectively controlled via natural attenuation processes. However, MTBE plume at Site A has migrated to a farther downgradient area and passed the boundary line of the site. Thus, more active groundwater remedial technologies should be applied at Site A to protect the downgradient environment. Results from this study suggest that natural attenuation might be feasible to be used as a remedial option for the remediation of MTBE-contaminated site on the premise that (1) detailed site characterization has been conducted and (2) the occurrence and effectiveness of natural attenuation processes have been confirmed.
Journal of Hazardous Materials 11/2005; 125(1-3):10-6. · 4.17 Impact Factor
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Bulletin of Environmental Contamination and Toxicology 02/2004; 72(1):87-93. · 1.02 Impact Factor
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ABSTRACT: Recently, the appearance of assimilable organic carbon (AOC) in the water treatment system and effluent of the treatment plant has brought more attention to the environmental engineers. In this study, AOC removal efficiency at the Cheng-Ching Lake water treatment plant (CCLWTP) was evaluated. The main objectives of this study were to: (1) evaluate the treatability of AOC by the advanced treatment system at the CCLWTP, (2) assess the relativity of AOC and the variations of other water quality indicators, (3) evaluate the effects of sodium thiosulfate on AOC analysis, and (4) evaluate the efficiency of biofiltration process using granular activated carbon (GAC) and anthracite as the fillers. Results show that the averaged influent and final effluent AOC concentrations at the CCLWTP were approximately 124 and 30 μg acetate-C/L, respectively. Thus, the treatment plant had an AOC removal efficiency of about 76%, and the AOC concentrations in the final effluent met the criteria established by the CCLWTP (50 μg acetate-C/L). Results indicate that the biofiltration process might contribute to the removal of the trace AOC in the GAC filtration process. Moreover, the removal of AOC had a correlation with the decrease in concentrations of other drinking water indicators. Results from a column test show that GAC was a more appropriate material than anthracite for the AOC removal. Results from this study provide us insight into the mechanisms of AOC removal by advanced water treatment processes. These findings would be helpful in designing a modified water treatment system for AOC removal and water quality improvement.
Desalination.
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ABSTRACT: Methyl tert-butyl ether (MTBE) has been used as a gasoline additive to improve the combustion efficiency and to replace lead since 1978. Because it is widely used and it has been disposed inappropriately, MTBE has become a prevalent groundwater contaminant worldwide. In this study, two petroleum-hydrocarbon contaminated sites (Sites A and B) were selected to evaluate the occurrence and effectiveness of natural attenuation of MTBE at these two sites. Field investigation results indicate that the natural attenuation mechanisms of MTBE at both sites were occurring with the first-order attenuation rates of 0.0021 and 0.0048 1 day−1 at Sites A and B, respectively. Results also reveal that the intrinsic biodegradation pattern was the most important mechanism among the natural attenuation processes at both sites. Results from BIOSCREEN simulation suggest that biodegradation was responsible for 78 and 59% of MTBE mass reduction at Sites A and B, respectively. Investigation results show that MTBE plume at Site B could be effectively controlled via natural attenuation processes. However, MTBE plume at Site A has migrated to a farther downgradient area and passed the boundary line of the site. Thus, more active groundwater remedial technologies should be applied at Site A to protect the downgradient environment. Results from this study suggest that natural attenuation might be feasible to be used as a remedial option for the remediation of MTBE-contaminated site on the premise that (1) detailed site characterization has been conducted and (2) the occurrence and effectiveness of natural attenuation processes have been confirmed.
Journal of Hazardous Materials.
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ABSTRACT: The aims of this study were to evaluate the biodegradability of tetracyanonickelate (II) [K2[Ni(CN)4] (TCN) by Klebsiella oxytoca under anaerobic conditions. Anaerobic serum bottles and fermenter experiments were conducted to evaluate the effects of nitrogen sources and pH on the TCN biodegradation potential by K. oxytoca. Results reveal that TCN can be biotransformed to methane by resting cells of K. oxytoca. Results show that TCN biodegradation was inhibited by the addition of nitrate, nitrite, or ammonia at higher concentrations (5 and 10 mM). Moreover, it was found that the optimum pH for TCN conversion by K. oxytoca was about 7.1. Results from the fermenter experiment show that TCN can be completely degraded within 14 days. K. oxytoca is capable of using TCN as the nitrogen source under anaerobic conditions. TCN could be biotransformed to non-toxic end product (methane) by resting cells of K. oxytoca. Higher TCN biodegradation rate can be obtained under alkaline conditions. This study provides us insight into the characteristics of TCN conversion by K. oxytoca under anaerobic conditions. These findings would be helpful in designing a practical system inoculated with K. oxytoca for the treatment of cyanide-containing wastewater.
Desalination. 249(3):1212-1216.
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ABSTRACT: This study investigated the feasibility of applying ozone (O3) to reduce the color content of wastewater caused by two commercial reactive dyes (Blue-19 and Orange-13). In the bench-scale experiment, experimental parameters including pH, ozone dosage, and reaction time were evaluated in a 14-L reactor to obtain the optimal operating conditions. Results show that ozone dosage and pH dominated the effectiveness of the decolorization process. The color content could be reduced from 2000 to 200 ADMI (American Dye Manufacture Institute) values within a reaction time of 30 min with the ozone input rate of 2.66 g/h. The pH values of 3 and 10 favored decolorization of Blue-19 and Orange-13, respectively. This was due to the effects that reactive and oxidizing species of molecular ozone and hydroxyl radicals were predominant at low and high pH, respectively. Moreover, molecular ozone was more selective to certain dye structures during the oxidation process. Kinetic analyses show that decolorization of Orange-13 and Blue-19 followed first-order kinetics. The degree of decolorization was primarily proportional to the ozone dosage. Results from this study provide insights into the characteristics and mechanisms of decolorization by the O3 technique. Results will also aid in designing a system for practical application.
Desalination.
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ABSTRACT: The main objective of this study was to examine the efficacy and capacity of using constructed wetlands on industrial pollutant removal. Four parallel pilot-scale modified free water surface (FWS) constructed wetland systems [dimension for each system: 4-m (L) × 1-m (W) × 1-m (D)] were installed inside an industrial park for conducting the proposed treatability study. The averaged influent contains approximately 170 mg l−1 chemical oxygen demand (COD), 80 mg l−1 biochemical oxygen demand (BOD), 90 mg l−1 suspend solid (SS), and 32 mg l−1 NH3–N. In the plant-selection study, four different wetland plant species including floating plants [Pistia stratiotes L. (P. stratiotes) and Ipomoea aquatica (I. aquatica)] and emergent plants [Phragmites communis L. (P. communis) and Typha orientalis Presl. (T. orientalis)] were evaluated. Results show that only the emergent plant (P. communis) could survive and reproduce with a continuous feed of 0.4 m3 d−1 of the raw wastewater. Thus, P. communis was used in the subsequent treatment study. Two different control parameters including hydraulic retention time (HRT) (3, 5, and 7 d) and media [vesicles ceramic bioballs and small gravels, 1 cm in diameter] were examined in the treatment study. Results indicate that the system with a 5-d HRT (feed rate of 0.4 m3 d−1) and vesicles ceramic bioballs as the media had the acceptable and optimal pollutant removal efficiency. If operated under conditions of the above parameters, the pilot-plant wetland system can achieve removal of 61% COD, 89% BOD, 81% SS, 35% TP, and 56% NH3–N. The treated wastewater meets the current industrial wastewater discharge standards in Taiwan.
Chemosphere.
