Shian-Chee Wu

Sorption kinetics of hydrophobic organic compounds to natural sediments and soils.

Sorption kinetics of hydrophobic organic chemicals to and from suspended sediment and soil particles is described by a radial diffusive penetration model modified by a retardation factor reflecting microscale partitioning of the sorbate between intraaggregate pore fluids and the solids making up the aggregate grains. In light of this and other sorption kinetics models, a closed-loop-stripping apparatus with a photoionization detector operating in-line was used to examine the effects of sorbate hydrophobicity, sorbent particle size, and system temperature on solid-solution exchange over times of seconds to days. The authors results indicate that a single effective diffusivity parameter, which is predictable from compound solution diffusivity, octanol-water partition coefficient, and sorbent organic content, density, and porosity, can be used to quantify the sorption kinetics.

Stability of metal oxide nanoparticles in aqueous solutions

The application of nanoparticles in the processes of making commercial products has increased in recent years due to their unique physical and chemical properties. With increasing amount of commercial nanoparticles released into nature, their fate and effects on the ecosystem and human health are of growing concern. This study investigated the stability and morphology of three metal oxide nanoparticles in aqueous solutions. The commercially available nanoparticles, TiO(2), ZnO, SiO(2), aggregated quickly into micrometer-size particles in aqueous solutions, which may not threaten human health. Their changes in morphology and characteristics were further examined by dynamic light scattering (DLS) method and transmission electron microscopy (TEM). Among the several dispersion approaches, ultrasonication was found to be the most effective for disaggregating nanoparticles in water. For these three selected nanoparticles, ZnO could not remain stable in suspensions, presumably due to the dissolution of particles to form high concentration of ions, resulting in enhanced aggregation of particles. In addition, the existence of dissolved organic matters stabilized nanoparticles in lake water and wastewater for several hours in spite of the high concentration of cations in these real-water samples. The fate of metal oxide nanoparticles in natural water bodies would be determined by the type and concentration of cations and organic matters. Results obtained in this study revealed that the stability of nanoparticles changed under different aqueous conditions and so did their fate in the environment.

The enhancement methods for the degradation of TCE by zero-valent metals

Batch tests were performed to compare the degradation rates of TCE on Fe0 and Zn0. Our results indicated that the degradating capability of Zn0 to TCE was nearly 10 times higher than that of Fe0. On the other hand, the degradation rates of Fe0 or Zn0 in conjunction with other metals for reduction of TCE was investigated. The selected metals were nickel (Ni0) and palladium (Pd0) both of which have a strong enhancement effect. The reduction rates of Zn0/Pd0 and Zn0/Ni0 for TCE were the fastest. Fe0 that had lost its surface activity could be activated again by the addition of Pd0 or Ni0.

Influence of nanoscale zero-valent iron on geochemical properties of groundwater and vinyl chloride degradation: A field case study

A 200m(2) pilot-scale field test successfully demonstrated the use of nanoscale zero-valent iron (NZVI) for effective remediation of groundwater contaminated with chlorinated organic compounds in Taiwan within six months. Both commercially available and on-site synthesized NZVI were used. A well-defined monitoring program allowing to collect three-dimensional spatial data from 13 nested multi-level monitoring wells was conducted to monitor geochemical parameters in groundwater. The degradation efficiency of vinyl chloride (VC) determined at most of monitoring wells was 50-99%. It was found that the injection of NZVI caused a significant change in total iron, total solid (TS) and suspended solid (SS) concentrations in groundwater. Total iron concentration showed a moderate and weak correlation with SS and TS, respectively, suggesting that SS may be used to indicate the NZVI distribution in groundwater. A decrease in oxidation-reduction potential (ORP) values from about -100 to -400mV after NZVI injection was observed. This revealed that NZVI is an effective means of achieving highly reducing conditions in the subsurface environment. Both VC degradation efficiency and ORP showed a correlative tendency as an increase in VC degradation efficiency corresponded to a decrease of ORP. This is in agreement with the previous studies suggesting that ORP can serve as an indicator for the NZVI reactivity.

Characterization and composition of heavy metals and persistent organic pollutants in water and estuarine sediments from Gao-ping River, Taiwan.

The objective of this study was to determine the concentrations and possible sources of heavy metals and persistent organic pollutants (POPs) in water and estuarine sediments from Gao-ping River in order to evaluate the environmental quality of aquatic system in southern Taiwan. High concentrations of heavy metals including Cr, Zn, Ni, Cu and As, ranging from 10.7 to 180 mg/kg-dry weight (dw), were detected in sediments from Gao-ping River. When normalized to the principal component analysis (PCA), swinery and electroplating wastewaters were found to be the most important pollution sources for heavy metals. Of various organochlorine pesticide (OCP) residues detected, aldrin and total-hexachlorocyclohexane (HCH) were frequently found in sediments. The total concentrations of OCPs were in the range 0.47-47.4 ng/g-dw. Also, the total-HCH, total-cyclodiene, and total-dichlorodiphenyltrichloroethane (DDT) were in the range 0.37-36.3, 0.21-19.0, and 0.44-1.88 ng/g-dw, respectively. The polychlorinated biphenyl (PCB) concentrations in sediments from Gao-ping River ranged between 0.37 and 5.89 ng/g-dw. The PCB concentrations are positively correlated to the organic contents of the sediment particles. alpha-HCH was found to be the dominant compound of HCH in the sediments, showing that long-range transport may be the possible source for the contamination of HCH in sediments from Gao-ping River. In summary, trace amounts of POPs in estuarine sediments from Gao-ping River were detected, showing that there still exist a wide variety of POP residues in the river sediments in Taiwan. These POP residues may be mainly from long-range transport and weathered agricultural soils, while heavy metal contamination is primarily from the swinery and industrial wastewaters.

Biodegradable surfactant stabilized nanoscale zero-valent iron for in situ treatment of vinyl chloride and 1,2-dichloroethane.

Nanoscale zero-valent iron (NZVI) stabilized with dispersants is a promising technology for the remediation of contaminated groundwater. In this study, we demonstrated the use of biodegradable surfactant stabilized NZVI slurry for successful treatment of vinyl chloride (VC) and 1,2-dichloroethane (1,2-DCA) in a contaminated site in Taiwan. The biodegradable surfactant stabilized NZVI was coated with palladium and synthesized on-site. From monitoring the iron concentration breakthrough and distribution, it was found that the stabilized NZVI is capable of transporting in the aquifer at the test plot (200 m(2)). VC was effectively degraded by NZVI while the 1,2-DCA degradation was relatively sluggish during the 3-month field test. Nevertheless, as 1,2-DCA is known to resist abiotic reduction by NZVI, the observation of 1,2-DCA degradation and hydrocarbon production suggested a bioremediation took place. ORP and pH results revealed that a reducing condition was achieved at the testing area facilitating the biodegradation of chlorinated organic hydrocarbons. The bioremediation may be attributed to the production of hydrogen gas as electron donor from the corrosion of NZVI in the presence of water or the added biodegradable surfactant serving as the carbon source as well as electron donor to stimulate microbial growth.

Feasibility of using metals to remediate water containing TCE

The feasibility of treating underground water contaminated by a chlorinated organic compound with bimetallics Fe/ Ni, Zn/Ni and Zn single metal was studied. Column tests to simulate a reactive permeable wall in a funnel-and-gate system were used. Research results indicated that bimetallic Fe0/Ni0 and Zn0/Ni0 all had a very strong degraded power to trichloroethylene (TCE) at concentration up to 25 mg/l under different flow rates (27 cm/day-20 m/day). Furthermore, the concentrations of TCE and various ions in the treated effluent were nearly lower than the values specified in related standards for drinking water in Taiwan. These results showed that this technique could be effectively and safely used as an underground water remediation process.

Partition coefficients of organochlorine pesticides on soil and on the dissolved organic matter in water

The partition coefficients of organochlorine pesticides (OCPs) between the organic matter of Taichung soil and water (Koc) were evaluated with batch-type experiments. The partition coefficients of OCPs between Aldrich humic acid and water (Kdoc) were estimated with solubility enhancement method as well. In this study, the Kocs of aldrin, heptachlor, and p,p′-DDT are greater than their Kdocs, and the relationship of dieldrin and heptachlor epoxide are opposite. The variations of partition coefficients are discussed. For predicting Kdoc, a log-log regression relationship of Kdoc and Kow is determined.

Reductive dechlorination of chlorinated hydrocarbons in aqueous solutions containing ferrous and sulfide ions

Abstract The transformation of volatile chlorinated hydrocarbons in aqueous phase containing free ferrous and sulfide ions with and without light irradiation were investigated to evaluate the effect of these reducing ions on the dechlorination of chlorinated hydrocarbons. In the presence of the ferrous ion alone, 84% of the original carbon tetrachloride (CT) was transformed to chloroform within 33 days, and a removal efficiency of 99% was reached when the solution was irradiated by visible light. However, carbon tetrachloride did not appear to be reactive in other media containing sulfide and/or bound ferrous ions. 1,1,1-trichloroethane and tetrachloroethylene were less susceptible than carbon tetrachloride to the reductive dechlorination. No transformation was observed for these two compounds in different types of media in 33 days. Oxidationreduction potential (ORP) measurements showed that carbon tetrachloride could be depleted only when ORP of the environment was below 360 mV (relative to standard hydrogen electrode). This study indicates that free ferrous ion is an active reducing agent for the dechlorination of CT, but has little effect on the transformation of 1,1,1-trichloroethane and tetrachloroethylene, whereas, free sulfide and bound ferrous ions do not appear to have the capability of dechlorination for these heavily chlorinated hydrocarbons.

Effect of substrate concentration on the biotransformation of carbon tetrachloride and 1,1,1-trichloroethane under anaerobic condition

Abstract The biotransformabilities of 1,1,1-trichloroethane (TCA) and carbon tetrachloride (CT) were investigated at 35°C under low concentration of acetic acid as the auxiliary substrate to evaluate the concentration effect of the auxiliary substrate on the biotransformation of the chlorinated hydrocarbons. Data shown in this study demonstrated that concentration of acetic acid could change the dechlorination capability of the microorganisms and, thus, influence the biotransformation of chlorinated hydrocarbons. The rate of the biotransformation of CT and TCA in the concentration range of 100–1000 μg/l increased progressively with the increase of the substrate concentration ranged from 0 to 30 mg/l. Nearly complete biotransformation of CT was obtained in 32 days. TCA was degraded slower than CT and removal of 20–91% was observed in 85 days, depending on the concentrations of both the primary substrate and the chlorinated compound. These removal efficiencies corresponded to second-order rate coefficients of 0.0006–0.0041 l/mg-VSS/d and 2.75 × 10 −5 to 2.97 × 10 −4 l/mg-VSS/d for CT and TCA, respectively. Available substrate supply is essential for the dechlorination of chlorinated compounds which is demonstrated by the experimental results showing the effects of the substrate concentration and the compound concentration. Also, the difference between the oxidation-reduction potentials of these two chlorinated hydrocarbons gives a possible explanation for the difference of the biotransformabilities of CT and TCA under some substrate conditions.