Search

Trichloroethylene (TCE) is one of the most ubiquitous halogenated organic compounds of concerns of carcinogens in groundwater in Taiwan. Bioremediation has been recognized as a cost-effective approach in reducing TCE concentration. Five pilot-scale wells were constructed to monitor TCE concentrations in contaminated groundwater. With injection of EOS®, TCE was effectively degraded to 42%–93% by the end of 175 days. The biostimulation with EOS® was useful in establishing a micro-site anaerobic but with limited contribution. Dilution of the aquifer movement also caused the TCE reduction among injection and monitoring wells. The degradability was affected by the location and the proximity from the injection well. TCE concentrations found to be negatively correlated with the associated Dehalococcoides spp. and functional genes levels. Dhc concentration of 108 copies L−1 caused the initial 40% of TCE degradation. The well with the optimal degradation owned tceA of 109 cells L−1. T-RFLP results indicate the wells with the superior TCE degradability also performed the highest Shannon index number (means the highest diversity), which occurred on the same day that Dhc levels started to enlarge. Desulfovibrio desulfuricans and Desulfuromonas chloroethenica were predominant species identified in the T-RFLP fingerprint profile. In brief, a variety of different factors including well locations, geochemical indicators, and microbial contribution were useful to explain the site-specific optimal TCE remediation approach. The consistence among TCE degradation, Dhc growing pattern, functional gene levels, and the dynamics of the microbial community structure present the novelty of this study.

A model approach is developed to simulate the adsorption isotherms of low-molecular-weight polar organic compounds (LMWPOCs), halogenated LMWPOCs, and dye molecules onto activated carbons (AC). The models were based on the Dubinin–Astakhov equation, with the limiting pore volume of adsorbent estimated from the pore size distribution data, and the adsorption affinity of the adsorbate described by the molecular connectivity index. The models were used to simulate the adsorption data of 87 LMWPOCs onto six ACs, 25 halogenated LMWPOCs onto two ACs and 22 dyes onto three ACs. The developed models follow the experimental data fairly well, with errors of 49, 33 and 43% for the tested LMWPOCs, halogenated LMWPOCs, and dyes, respectively. This study shows that the developed model approach may provide a simple means for the estimation of adsorption capacity for LMWPOCs and dyes onto ACs in water.

A new model is developed to predict the competitive adsorption isotherms of atrazine, methyl tertiary butyl ether (MTBE), 2-methylisoborneol (2-MIB) and 2,4,6-trichlorophenol onto activated carbons (ACs) in natural water. Based on the Polanyi-Dubinin (PD) equation, with the limiting pore volume of adsorbent estimated from the pore size distribution data, and the Ideal adsorbed solution theory - equivalent background compound (IAST-EBC) model approximation, the model takes into account both the properties of ACs and the impact of natural organic matters in water. Only one set of isotherm in deionized water and one set in natural water are needed to obtain the parameters for the prediction of adsorption isotherms onto different ACs in natural water. The model was employed for the predictions of adsorption capacities for atrazine, MTBE, 2-MIB and 2,4,6-trichlorophenol onto 14 ACs in 22 synthetic and natural waters reported in 9 references, with errors between 14.9% and 44.5% SDEV only. The results suggest that in the proposed PD-IAST-EBC approach, prediction of adsorption capacity for organic compounds onto different ACs in the same natural water is feasible, if the ACs are thermally activated with known pore size information. The model may provide a simple approach for the prediction of adsorption of organic compounds in natural water, and thus greatly reduces the effort required for water utilities when change of AC is needed.

The addition of powdered activated carbon (PAC) is an effective measure to cope with seasonal taste and odor (T&O) problems caused by 2-methylisoborneol (2-MIB) and trans-1, 10-dimethyl-trans-9-decalol (geosmin) in drinking water. Some T&O problems are episodic in nature, and generally require rapid responses. This paper proposed a simplified approach for the application of the homogenous surface diffusion model (HSDM) to predict the appropriate PAC doses for the removal of 2-MIB. Equilibrium and kinetic experiments were performed for 2-MIB adsorption onto five PACs in three source waters. The simplified HSDM approach was compared with the experimental data, by assigning the Freundlich 1/n value in the range of 0.1-1.0 and obtaining the Freundlich equilibrium parameter K value through a 6-hr adsorption kinetic test. The model describes the kinetic adsorption data very well for all of the tested PACs in different source waters. The results were validated using the data obtained from one full scale water treatment plant, and the differences between the predicted and observed results were within 10% range. This simplified HSDM approach may be applied for the rapid determination of PAC doses for water treatment plants when faced with 2-MIB episodes in source waters.

Enhanced monitored natural attenuation was conducted with molasses injections to an in situ trichloroethylene (TCE)-contaminated groundwater site. Three pilot-scale wells were conducted for monitoring and substrate injections. At most 97.0% of the TCE was effectively degraded after about 600 days. TCE detected in the injection wells attained Tier 2 Groundwater Regulation in Taiwan for non-drinking water sources. The reaction rates of Cl–VOCs in one of the injection wells explained the mechanism how these dechlorinating species transferred TCE to cis-DCE and VC in anaerobic conditions. The magnitude of the 1st order kinetic growth rates of Dehalococcoides (Dhc) were consistent with the associated TCE degradability. The qPCR and T-RFLP results concluded existence of crucial dechlorinating species including Dhc, which performed critical level of 106 copy L−1 to trigger the TCE degradation. The detected tceA and vcrA ranging from 2.07 × 103 to 6.57 × 105 copy L−1confirmed the pathway of TCE degradation. The two injection wells with the optimal TCE degradation showed increases of bacterial diversity estimated by the Shannon Index. The Shannon index explained the superiority of an increased bacterial diversity. The nonmetric multidimensional scaling results suggested that the bacterial dynamic was affected by the TCE degradation stages. The bacterial community structures were analogous when TCE was well degraded.

Black carbons (BCs) may sequester non-ionic organic compounds by adsorption and/or partition to varying extents. Up to now, no experimental method has been developed to accurately resolve the combined adsorption and partition capacity of a compound on a BC. In this study, a unique "adsorptive displacement method" is introduced to reliably resolve the adsorption and partition components for a solute-BC system. It estimates the solute adsorption on a BC by the use of an adsorptive displacer to displace the adsorbed target solute into the solution phase. The method is validated by tests with uses of activated carbon as the model carbonaceous adsorbent, soil organic matter as the model carbonaceous partition phase, o-xylene and 1,2,3-trichlorobenzene as the reference solutes, and p-nitrophenol as the adsorptive displacer. Thereafter, the adsorption-partition resolution was completed for the two solutes on selected model BCs: four biochars and two National Institute of Standards and Technology (NIST) standard soots (SRM-2975 and SRM-1650b). The adsorption and partition components resolved for selected solutes with given BCs and their dependences upon solute properties enable one to cross-check the sorption data of other solutes on the same BCs. The resolved components also provide a theoretical basis for exploring the potential modes and extents of different solute uptakes by given BCs in natural systems.

In order to differentiate genetically-similar diesel fuel supplied from two refinery companies in Taiwan, an approach using diagnostic ratios (DRs) among numerous source-specific diesel range marker compounds and principal component analysis (PCA) was utilized. A total of 267 fresh diesel samples [141 biodiesels (BDs) and 126 premium diesels (PDs)] were obtained from gasoline stations supplied by one of two refinery companies in Taiwan, referred to herein as A and B. The compounds used in the PCA–DRs approach for distinguishing diesel fuels from these two refinery company sources included bicyclic sesquiterpanes, adamantanes, and alkylated polycyclic aromatic hydrocarbons (PAHs). The PCA–DRs approach utilizing 45 and 41 DRs has the ability to distinguish between all of the fresh BD and PD, respectively, from refinery companies A and B. To evaluate the PCA–DRs approach in weathered diesel fuel, the approach was preliminary applied to the petroleum-contaminated Site F, which was impacted with gasoline and PD spilled in 2007. Only DRs unaffected by weathering were utilized in assessing the source of the diesel fuel in samples from Site F, and indicated refining company A to be the source. The approach also successfully used 36 DRs or 18 DRs with the greatest diagnostic power (>5) for evaluating variably weathered diesel fuel contamination at six spilled sites, and distinguished those impacted by diesel fuels from refining companies A and B. Thus, by selecting the most appropriate and distinguishing DRs, the PCA–DRs approach described herein can be used to differentiate both fresh and weathered diesel fuels produced from different refinery companies present at contaminated sites in Taiwan.

As a solution theory, Raoult’s law is commonly used to estimate the activities of solutes and solvents of comparable molecular sizes while the Flory–Huggins (F–H) model is used for the activities of small liquids in high polymers. For a great many systems where the solute and solvent differ only moderately in molecular size (e.g., by 4–10 times), there has been no confirmed choice of a preferred model; examples of such systems are those of ordinary organic compounds in liquid triolein (MW = 885.4 g·mol−1) and poly(propylene glycol) (PPG) (MW = ~1,000 g·mol−1). The observed nearly athermal solubilities of many nonpolar organic solids in these solvents provide unique experimental data to examine the merit of a solution model. As found, Raoult’s law underestimates widely, and the F–H model underestimates slightly, the solid solubilities in triolein and PPG because these models underestimate the solution entropy for these solute–solvent pairs. To rectify this problem, the molecular segments of a large sized liquid solvent (e.g., triolein) are assumed to act as independent mixing units to increase the solute–solvent mixing entropy. This adjustment leads to a modified F–H model in which the “ideal” or “athermal” solubility of a solid in volume fraction, at a particular temperature, is equal to the solid’s activity at that temperature. Results from other studies give further support for the modified F–H model to interpret the partition data of compounds with organic solvents.

2-Methylisoborneol (2-MIB) and trans-1,10-dimethyl-trans-9-decalol (geosmin) are two commonly observed taste and odor compounds present in drinking water sources. The effects of pH on the analysis of the two chemicals are investigated using a gas chromatograph and mass spectrometric detector (GC/MSD) coupled with three pre-concentration methods, namely solid-phase micro-extraction (SPME), purge-and-trap concentration (PTC), and liquid–liquid extraction (LLE). At neutral and alkaline pH conditions, the concentrations detected for both compounds remain constant. However, a substantial reduction of concentration for both chemicals is observed when the water solution pH is less than 5. Under acidic conditions (pH ≅ 2.5), the 2-MIB concentrations detected by GC/MSD coupled with SPME, PTC, and LLE are 87%, 16%, and 37% lower than those measured at pH 6–7, respectively. For geosmin, a decrease in concentration is only observed when using GC/MSD-SPME, presumably due to the higher extraction temperature compared to the other two techniques. The pH-dependent behavior was attributed to dehydration of the tertiary alcohols of 2-MIB and geosmin under acidic conditions. The dehydration for 2-MIB and geosmin is reversible, and the analysis can be mitigated by adjusting the water solution pH back to a neutral condition.

A new model approach is developed to predict the adsorption isotherms of low-molecular-weight nonpolar organic compounds (LMWNPOCs) onto activated carbons (ACs). The model is based on the Polanyi-Dubinin (PD) equation, with the limiting pore volume of adsorbent estimated from the pore size distribution (PSD) data, and the adsorption affinity of adsorbate described by the molecular connectivity index (MCI). To obtain the MCI parameters, the model was first tested for the adsorption of 34 LMWNPOCs primarily on F400 AC from 3 reports. The models fit the experimental data well, with only 39.2% of errors. The approach was further employed to predict the adsorption capacity of 40 LMWNPOCs on F400 AC, 12 LMWNPOCs onto 9 other ACs, and 8 LMWNPOCs onto 5 ACs with unknown PSD, with the errors of 41.9%, showing the model being reasonable. The model approach may provide a simple means for predicting adsorption capacities of LMWNPOCs onto different ACs.

In view of the scarcity of the lipid-water partition coefficients (Ktw) for organic compounds, the logKtw values for many environmental contaminants were measured using ultra-pure triolein as the model lipid. Classes of compounds studied include alkyl benzenes, halogenated benzenes, short-chain chlorinated hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and organochlorine pesticides. In addition to logKtw determination, the uptakes of these compounds from water by a dry algal species were measured to evaluate the lipid effect on the algal uptake. The measured logKtw are closely related to their respective logKow (octanol-water), with logKow=1.9 to 6.5. A significant difference is observed between the present and early measured logKtw for compounds with logKow>∼5, which is attributed to the presence and absence of a triolein microemulsion in water affecting the solute partitioning. The observed lipid-normalized algae-water distribution coefficients (logKaw/lipid) are virtually identical to the respective logKtw values, which manifests the dominant lipid-partition effect of the compounds with algae.

The sorption of phenanthrene (PHN) to relatively pure soil humic acids (HAs) was investigated to assess the suitability of the soil HA as a surrogate sorbent for the soil organic matter (SOM). The HAs were prepared in both freeze-dried and air-dried forms. The two forms of HAs from the same source are similar in composition but the freeze-dried HAs exhibit a significantly higher initial surface area (SA) (3.86-4.59 m(2)/g); the SAs of air-dried HAs are below 0.1 m(2)/g. However, the SAs of freeze-dried HAs are not stable upon contact with water; the samples lose practically all the SA after 4 days of immersion in water. The PHN sorption to both forms of HAs is practically linear, whether a co-solute is present or not. The sorption linearity observed with the present freeze-dried HAs is in sharp contrast with the allegedly nonlinear PHN sorption on similar freeze-dried HAs as presented by others.