Model Simulation of Diurnal Vertical Migration Patterns of Different-Sized Colonies of Employing a Particle Trajectory Approach.

, a genus of potentially harmful cyanobacteria, is known to proliferate in stratified freshwaters due to its capability to change cell density and regulate buoyancy. In this study, a trajectory model was developed to simulate the cell density change and spatial distribution of cells with nonuniform colony sizes. Simulations showed that larger colonies migrate to the near-surface water layer during the night to effectively capture irradiation and become heavy enough to sink during daytime.

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.

Simultaneous estimation of glass-water distribution and PDMS-water partition coefficients of hydrophobic organic compounds using simple batch method.

A simple batch method by use of refilling and nonrefilling experimental procedures and headspace solid phase microextraction was applied to simultaneously obtain the glass-water distribution coefficients (K(GW)) and polydimethylsiloxane(PDMS)-water partition coefficients (K(PW)) of hydrophobic organic compounds (HOCs). The simple batch method takes into consideration the glass-surface bound HOCs and the corresponding equilibrium distribution of HOCs among the glass, water, headspace, and polydimethylsiloxane (PDMS). The K(PW) and K(GW) values of 53 PCB congeners were determined.

Development of a trajectory model for predicting attachment of submicrometer particles in porous media: stabilized NZVI as a case study.

A new trajectory simulation algorithm was developed to describe the efficiency of a single collector (pore) to catch submicrometer particles moving through saturated porous media. A constricted-tube model incorporating the deterministic (interception, hydrodynamic retardation, van der Waals force and gravitational sedimentation), stochastic (Brownian diffusion), and thermodynamic (electrostatic and steric repulsion force) mechanisms was established to predict the transport and deposition of surface modified nanoscale zerovalent iron (NZVI) particles by applying Lagrangian trajectory analytical approach. The simulation results show good agreement with the results predicted by existing energy-barrier-free models except for the particle size less than 100 nm at low approach velocity.

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.

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.

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.

Sorption kinetics of toluene in humic acid: a computational approach.

Molecular dynamics, a computational technique aiming to describe the time-dependent movement of molecules, has been applied to study the sorption kinetics of volatile organic contaminants in soil organic matter. The molecular dynamics simulation results obtain reasonably accurate estimates of diffusion rates and activation energy of the penetration of a volatile organic compound molecule into a model humic substance. The sorption rate of toluene to humic acid decreases with the density of the humic acid matrix and increases with temperature.

Distinctive sorption mechanisms of soil organic matter and mineral components as elucidated by organic vapor uptake kinetics.

Sorption kinetics and capacities of volatile organic compounds (VOCs) affect the remediation and fate of these pollutants in soils. The soil organic-mineral compositional heterogeneity complicates the transport and fate of VOCs in soils. The sorption kinetics of toluene vapor with two common soil components, kaolinite and humic acid, shows two distinct sorption patterns.

Bioaccumulation of polychlorinated biphenyls in mullet fish in a former ship dismantling harbour, a contaminated estuary, and nearby coastal fish farms.

This study investigated the bioaccumulation of polychlorinated biphenyls (PCBs) toward mullet fish (Liza macrolepis) living in former PCB contaminated areas, the Ann-Ping harbour and the Er-Jen estuary, and fish farms located near the above two areas in 2003. The PCB body burdens of collected fish samples are proportional to the contamination level of their locations with the following rank order (greatest to least) from the Er-Jen estuary, the Ann-Ping harbour to the fish farms. Concentration of PCBs of the estuarine mullet has been approximately decreased to one-half of the peak concentration of the 1990s.

Seasonal variation of the distribution of PCBs in sediments and biota in a PCB-contaminated estuary.

To elucidate the effects of seasonal variation of precipitation on the distribution of polychlorinated biphenyls (PCBs) in estuarine sediments and benthic feeders, PCB concentrations of river surface sediments and mullet fish (Liza macrolepis) were investigated in the estuary of Er-Jen River near former PCB contamination sites before and after each wet season from 2002 to 2004. Analyses of grain size distribution and organic matter revealed that the pre-existing surface sediments were covered by and mixed with the soil particulates brought by surface runoff after each wet season. Obvious increment of PCB content and significantly elevated fraction (p<0.

Kinetics of toluene sorption and desorption in Ca- and Cu-montmorillonites investigated with Fourier transform infrared spectroscopy under two different levels of humidity.

Clays in soils or groundwater aquifer materials play roles in the sorption of organic pollutants. The intrinsic sorption kinetics of toluene in dry and humid clay films was investigated by tracking the change of infrared absorbance. Under the humid condition, similar toluene-sorbed intensities were found in Ca- and Cu-montmorillonites.

Infrared investigation of the sequestration of toluene vapor on clay minerals.

The Ca-exchanged clays were used to investigate the sorption of toluene under both high and low relative humidity conditions. According to the observed rates of sorption and desorption and the Fourier transform infrared (FTIR) spectra of sorbed toluene, the sorbate molecules on clays can be divided into three categories: labile (gaslike) phase, slow sorption (liquidlike) phase, and resistant-to-desorption phase with sorption/desorption time scales of less than 30 min, several hours, and several weeks, respectively. Aging changed the spectroscopic characteristics of the sorbed sorbates and contributed to the irreversibility of the sorption under both high and low relative humidity.

Sorption kinetics of selected volatile organic compounds in humin.

Each component of the chemically heterogeneous soil exhibits a unique sorption behavior toward organic sorbates. The sorption kinetics of some volatile organic compounds (VOCs) in pressed humin disks was investigated by tracking the weight change of the disks with a microbalance. Higher sorbing capacity for more polar VOCs as well as C13 nuclear magnetic resonance data indicates that humin was more hydrophilic than Aldrich humic acid (Milwaukee, WI, USA).

Distribution and fate of organochlorine pesticide residues in sediments from the selected rivers in Taiwan.

The contamination of organochlorine pesticides (OCPs) in sediments from selected rivers in Taiwan was investigated to evaluate the pollution potentials and hazard in river sediments. Da-han River and Erh-jen River were selected as the target rivers due to their serious pollution. A total of 40 surface sediment samples were collected at five sampling stations along the rivers.

Sorption kinetics of toluene in humin under two different levels of relative humidity.

To identify any resistant fraction for desorption of toluene from humin and to quantify the sorption-desorption rates, the time courses of toluene sorption to compressed humin disks and to a thin humin film were investigated. The apparent diffusivity of toluene with humin disks ranges from 10(-8) to 10(-9) cm2/s and increases with temperature, based on the weight change of humin disks mounted on a microbalance and on the results simulated by use of a diffusion model. No detectable level of residual toluene was found after desorption, as revealed either by the gravimetric analysis or by the Fourier transform infrared (FTIR) spectrum obtained at either low or high humidity.