Yu-Min Chang

Concentration and purification of chromate from electroplating wastewater by two-stage electrodialysis processes

A designed two-stage electrodialysis system is proposed to concentrate and purify chromate from a low pH electroplating wastewater using monovalent selective electrodialysis membranes. With low pH of the raw water (pH 2.2) in the first stage, chromate was presented as HCrO(4)(-) and monovalent ions (HCrO(4)(-), NH(2)SO(3)(-), Na(+) and Cl(-)) were able to pass through the membrane thus chromate was concentrated up to 191%. Higher current density, flowrate and more membrane area all increased the chromium recovery. When pH was adjusted to 8.5 before entering the second stage, the chromate species was presented as divalent CrO(4)(2-) and retained in the concentrated stream, and the rest monovalent ions (NH(2)SO(3)(-), Na(+) and Cl(-)) were separated by passing through the membrane. For example, 45% of the chlorides were separated in this study. The separation efficiencies in the second stage were also increased when the current density, flowrate and membrane area were increased. Electron Spectroscopy for Chemical Analysis was used to examine the surface chromate species for stage 1, and anion exchange membrane showed more chromate fouling comparing to cation exchange membrane due to more adsorption and concentration polarization effects for the anion exchange membrane.

Characteristics of PCDD/F content in fly ash discharged from municipal solid waste incinerators.

Different from most previous studies with quantity-limited data, this paper presents PCDD/F content characterization in the fly ash discharged from sixteen large-scale commercial MSWIs. From the results with over hundreds of data using periodically sampling and analysis, it was found that the PCDD/F contents in the fly ash were from 9.07 to 46.68ng/g, d.w., and if based on international toxicity equivalent quantity, they were from 0.78 to 2.86ng I-TEQ/g, d.w. The higher chlorinated PCDDs likely dominated more than lower chlorinated PCDDs, but this tendency was not for PCDFs. The OCDD had the highest contribution to the total PCDD/F content, but if based on I-TEQ content, 2,3,4,7,8-PeCDF is the PCDD/F congener with the highest toxicity contribution. Moreover, the PCDD/F characteristic index (DCI) is suggested using the representative congener content of 2,3,4,7,8-PeCDF to characterize the fly ash. The DCI is 0.875±7.6% for the fly ash discharged from the MSWI with the APCD assembly of SD, AC and BF. The findings obtained in this work provide overview information on the PCDD/F content characterization in fly ash. They will provide PCDD/F fingerprint information to distinguish from other PCDD/F sources, like steel refinery industry, hazardous waste incinerators, or cement kilns, and thus be applied to fly ash management in the environment.

Minimum feeding rate of activated carbon to control dioxin emissions from a large-scale municipal solid waste incinerator.

To obtain a minimum feeding rate (F(min)) of activated carbon (AC), a series of measurements on dioxin emission concentration were carried out in a large-scale municipal solid waste incinerator. It was found that dioxin removal efficiency (eta) increased with an increase in AC feeding concentration. This had an almost linear function to F/Q when F/Q was less than 65 g/Nm(3), where F was the AC feeding rate (mg/min), and Q was the volumetric flow rate of flue gas (Nm(3)/min). However, it did not seem to be affected by F/Q, when F/Q was larger than 150 mg/Nm(3). On the basis of the experimental data obtained in this study, the removal efficiency of dioxins by the application of AC could be correlated as eta (%)=100/[1.0+(40.2/(F/Q)(3))]. It is valid in appropriate conditions (F/Q=10-300 mg/Nm(3)) suggested by the study with a statistical error of +/-18%. The correlation would be applied to estimate the dioxin removal efficiency (eta) using the F/Q value. For engineering applications, the (F/Q)(min) could be solved using a graphic illustration method, by which the minimum feeding rate (F) was obtained if the flue gas volumetric flow rate (Q) was known.

Application of polycolloid-releasing substrate to remediate trichloroethylene-contaminated groundwater: a pilot-scale study.

The objectives of this pilot-scale study were to (1) evaluate the effectiveness of bioremediation of trichloroethylene (TCE)-contaminated groundwater with the supplement of slow polycolloid-releasing substrate (SPRS) (contained vegetable oil, cane molasses, surfactants) under reductive dechlorinating conditions, (2) apply gene analyses to confirm the existence of TCE-dechlorinating genes, and (3) apply the real-time polymerase chain reaction (PCR) to evaluate the variations in TCE-dechlorinating bacteria (Dehalococcoides spp.). Approximately 350L of SPRS solution was supplied into an injection well (IW) and groundwater samples were collected and analyzed from IW and monitor wells periodically. Results show that the SPRS caused a rapid increase of the total organic carbon concentration (up to 5794mg/L), and reductive dechlorination of TCE was significantly enhanced. TCE dechlorination byproducts were observed and up to 99% of TCE removal (initial TCE concentration=1872μg/L) was observed after 50 days of operation. The population of Dehalococcoides spp. increased from 4.6×10(1) to 3.41×10(7)cells/L after 20 days of operation. DNA sequencing results show that there were 31 bacterial species verified, which might be related to TCE biodegradation. Results demonstrate that the microbial analysis and real-time PCR are useful tools to evaluate the effectiveness of TCE reductive dechlorination.

A Study on Dynamic Volatile Organic Compound Emission Characterization of Water-Based Paints

ABSTRACT Volatile organic compounds (VOCs) emitted from surface coatings have caused growing public concern for air quality. Even the low-emitted VOC impact from water-based paints on indoor air quality in urban areas has caused concern. This paper presents experimental data using a mathematical model to simulate dynamic VOC emissions from water-based paints that is based on mass transfer and molecular diffusion theories. A series of field-analogous experiments were carried out to continuously measure the VOCs emitted from two typical water-based paints using a gas chromatography–flame-ionization detector monitor in an artificial wind tunnel system. In the study cases, the mass flux of VOCs emitted from the water-based paints was up to 50 μg/m2sec. It was found that the time needed to completely emit VOCs from water-based paints is just hundreds of seconds. However, the order of magnitude of the VOC emission rate from water-based paints is not lower than that from some dry building materials and solvent-based paints. The experimental data were used to produce a useful semiempirical correlation to estimate the VOC emission rates for water-based paints. This correlation is valid under appropriate conditions as suggested by this work with a statistical deviation of ±7.6%. With this correlation, it seems feasible to predict the dynamic emission rates for VOCs during a painting process. This correlation is applicable for assessing the hazardous air pollutant impact on indoor air quality or for environmental risk assessment. Associated with the dynamic VOC emission characterization, the air-exchange rate effect on the VOC emission rates is also discussed. IMPLICATIONS This paper presents experimental data using a mathematical model to simulate dynamic VOC emissions from water-based paints that is based on mass transfer and molecular diffusion theories. A semiempirical correlation is suggested to estimate the VOC emission rates for water-based paints. With this correlation, it is feasible to interpret and predict the dynamic emission rates for VOCs during a painting process. The results obtained in this work will be useful in evaluating the indoor air quality impact by primary VOCs or hazardous air pollutants emitted from water-based paints.

Reduction of PCDDs/PCDFs in MSWI fly ash using microwave peroxide oxidation in H2SO4/HNO3 solution.

Microwave peroxide oxidation (MPO) is an energy-efficient and low GHG emission technology to destroy the hazardous organic compounds in solid waste. The objective of this paper is to explore the reduction feasibility of PCDDs/Fs in MSWI fly ash using the MPO in H2SO4/HNO3 solution. Nearly all PCDDs/Fs, 99% in the original fly ash, can be reduced in 120min at the temperature of 150°C using the MPO treatment. It was also found that a change occurred in the content distribution profiles of 17 major PCDD/F congeners before and after MPO treatment. This provides the potential to reduce the actual PCDDs/Fs content more than I-TEQ contents of PCDDs/Fs. The percentile distribution profile has a tendency of higher chlorinated PCDDs/Fs moving to the lower ones. It concludes that a significant reduction efficiency of I-TEQ toxicity was achieved and showed sufficient reduction of toxic level to lower than 1.0ngI-TEQ(gdw)(-1). The treatment temperature would be a critical factor facilitating the dissolution because higher temperature leads more inorganic salt (parts of fly ash) dissolution. Some problems caused by the MPO method are also delineated in this paper.

Control of trichloroethylene plume migration using a biobarrier system: a field-scale study

The objective of this field-scale study was to evaluate the effectiveness of controlling trichloroethylene (TCE) plume migration using the polycolloid substrate (PS) biobarrier. The developed PS (containing soybean oil, lactate and surfactants) could release substrate to enhance the TCE dechlorination. In this study, a biobarrier comprising PS injection wells was installed. Injection wells were installed at 5-m intervals, and approximately 15 L of PS was injected into each well. Results show that TCE concentrations in the injection wells dropped from an average of 87 μg/L to below 1 μg/L after 35 days of PS injection. The total organic carbon concentrations in the injection wells increased from an average of 2.1-543 mg/L after 30 days of PS injection. The dissolved oxygen (DO) concentrations and oxidation-reduction potential (ORP) values dropped from an average of 1.6 mg/L to below 0.1 mg/L and from 124 mv to -14 mv after 20 days of injection, respectively. The DO and ORP remained in anaerobic conditions during the remaining 100 days of the operational period. TCE degradation by-products were observed in groundwater samples during the operational period. This reveals that the addition of PS could effectively enhance the reductive dechlorinating of TCE.

Recent management strategies for municipal solid wastes in Taiwan

Reduction and recycling initiatives being implemented in Taiwan include producer responsibility, pay-as-you-throw, and etc. The paper presents the recent management programs implemented for municipal solid waste, and also studies the change of characteristics for incineration-feeding waste to explore the influence of management strategies of MSW reduction and recycling on the waste characteristics. It is found that not only the annual amount of MSW generated in 2008 decreases about 5% than that in 2005, but also the characteristics of refuse have significant variability due to the recent management strategies. A comparison on monthly variation of chemical elements indicates that the chlorine content in refuse changes obviously. This would be the result from the usage reduction in PVC plastic due to the RFM program, and the food waste as well as salt content reduction due to the TKG program. This achievement would give a benefit to reduce the dioxins emission from MSW incineration. In summary, the management strategies must be conducted in tandem with the global trend to achieve a zero-waste-discharge country. It is important to consider the changes that may occur in the composition and characteristic of MSW with time in planning for future MSW management systems. All programs relative to MSW reduction management are worthy of notice.

Rapid reduction of lead leachate from hazardous fly ash using microwave treatment with acid combination

The novelty of this study is to rapidly reduce hazardous lead leachates from solid waste using microwave digestion treatment, which is an energy-saving and low greenhouse gas emission technology. The article presents the reduction of toxic characteristic leaching procedure-extractable lead concentration in the municipal solid waste incineration fly ash by the microwave digestion treatment in HNO3/H2SO4 combination, and focuses on the effects of treatment time and temperature. The results obtained from this study indicated a significant reduction efficiency of toxic characteristic leaching procedure-extractable lead concentration and showed sufficient reduction in leaching levels to render the treated fly ash safe in lead compound leaching characteristics. The reduction efficiency of toxic characteristic leaching procedure-extractable lead concentration can reach 98% in 15 minutes of treatment time. This is equivalent to the original toxic characteristic leaching procedure-extractable lead concentration of 46.2 mg L−1 in raw fly ash being reduced down to less than 1.0 mg L−1. Based on the experimental data obtained in this study, a useful correlation between reduction efficiency and treatment conditions is proposed. For engineering applications, the necessary minimum treatment time is solved using a graphic illustration method, by which the minimum treatment time (tmin) is obtained if the desired reduction efficiency (η) and treatment temperature (T) are known. The effects of treatment time and temperature are discussed. Some problems caused by the microwave digestion treatment method are also delineated in this article.

Bioremediation of 2,4,6-trinitrotoluene-contaminated groundwater using unique bacterial strains: microcosm and mechanism studies

Groundwater at many military factory, munition storage and maneuver sites is contaminated by explosives chemicals that were released into the subsurface. The 2,4,6-trinitrotoluene (TNT) is among the most common explosive pollutants. In this study, two TNT-degrading strains, isolated from TNT-contaminated soils and wastewater sludge, were applied for TNT biodegradation. Based on the 16S rDNA sequence analyses, these two bacterial strains were identified as Achromobacter sp. and Klebsiella sp. via biochemical and DNA analyses. Microcosm study was conducted to evaluate the feasibility and efficiency of TNT biodegradation under aerobic conditions. Results indicate that TNT degradation by-products were detected in microcosms (inoculated with Achromobacter sp. and Klebsiella sp.) with cane molasses addition. Klebsiella sp. and Achromobacter sp. used TNT as the nitrogen source and caused completely removal of TNT. Two possible TNT biodegradation routes could be derived: (1) part of the TNT was transformed to nitrotoluene then transformed to nitrobenzene followed by the nitro substitute process, and trinitrobenzene, dinitrobenzene, and nitrobenzene were detected; and (2) TNT was transformed via the nitro substitute mechanism, and dinitrotoluene followed by nitrotoluene isomers were detected. The initial TNT degradation involved the reduction or removal of the nitro substitute to an amino derivative or free nitrite. Results show that the second route was the dominant TNT biodegradation pathway. The produced by-products were also degraded without significant accumulation during the degradation process. These findings would be helpful in designing a practical system inoculated with isolated TNT degradation strains for the treatment of TNT-contained groundwater.