Winn-Jung Huang

Adsorption of mercury from water by modified multi-walled carbon nanotubes: adsorption behaviour and interference resistance by coexisting anions

This investigation reports the use of modified multi-walled carbon nanotubes (MWCNTs) with various functional groups for adsorbing inorganic divalent mercury (Hg(II)) from water samples. To elucidate the behaviours and mechanisms of Hg(II) adsorption by modified MWCNTs, their adsorption capacity was studied by considering adsorption isotherms and kinetics. Particular attention was paid to interference of coexisting inorganic ions with Hg(II) adsorption. The results reveal that functionalization with oxygen-containing groups improved the Hg(II) adsorption capacity of the MWCNTs. Kinetic analysis demonstrated that the adsorption of Hg(II) by MWCNTs was closely described by the pseudo-second-order and Elovich models, suggesting that the adsorption of Hg(II) by MWCNTs was significantly affected by chemical adsorption. The kinetic results were also analysed using the intraparticle diffusion model, which revealed that intraparticle diffusion was not the only rate-controlling mechanism. The adsorption of Hg(II) on MWCNTs fell drastically as the ionic strength increased from 0 to 1.0 mol/L chloride ions, and declined significantly as the pH increased from 2.2 to 10.5. The elemental maps obtained by energy-dispersive spectrometer (EDS) revealed the formation of surface complexes of chloride ions with functional groups on MWCNTs, which reduced the number of available sites for the adsorption of Hg(II) and strengthened the repulsive forces between Hg(II) and MWCNTs. The EDS results suggest that chloride ions are important in controlling Hg(II) speciation and adsorption on the surfaces of MWCNTs.

Study of Ambient Air Particle-Bound As(p) and Hg(p) in Dry Deposition, Total Suspended Particulates (TSP) and Seasonal Variations in Central Taiwan

This study investigated the ambient air particle-bound As(p) and Hg(p) levels and compositions in dry deposition and total suspended particulates (TSP) at five sampling sites in Central Taiwan (suburban/coastal, downtown, residential, industrial and wetland) during the years of 2009 and 2010. The main industrial sources of studied metals in various investigated sites include: steel, electronic, plastic, and chemical industries, the Taichung thermal power plant (TTPP), fossil fuel combustion, a science park, transportation, and waste incineration. The samples were digested with hydrochloric acid (HCl) and nitric acid (HNO3), then they were analyzed for metals by ICP-MS. The mean As(p) levels in dry deposition were the highest at Quan-xing site (industrial) and the lowest at Chang-hua site (downtown). Moreover, the mean Hg(p) levels in dry deposition were the highest at Gao-mei site (wetland) and the lowest at He-mei site (residential). In addition, the mean As(p) levels in TSP were the highest at He-mei site (residential) and the lowest at Gao-mei site (wetland). The mean Hg(p) levels in TSP were the highest at Quan-xing site (industrial) and the lowest at Gao-mei site (wetland). Regarding seasonal variation, the lowest levels in dry deposition for both particles As(p) and Hg(p) occurred in spring and summer. Finally, the lowest levels of As(p) and Hg(p) in TSP were observed in fall and winter.

Disinfection by-product formation and mutagenic assay caused by preozonation of groundwater containing bromide

Brominated organic and inorganic by-products are generated during ozonation of groundwater containing high bromide concentrations. This study measured concentrations of bromate, bromoform, bromoacetic acids, bromoacetonitriles, bromoacetone, 2,4-dibromophenol and aldehyde generated by ozonation. The potential mutagenicity of ozonated waters was assessed using the Ames and Microtox tests. Test results for the 18 ozonated groundwater samples demonstrate that bromate formation is associated with high pH, bromide and alkalinity content, low levels of dissolved organic carbon (DOC) and ammonia, and low alkalinity. Brominated organic by-products were correlated with high bromide ion and natural organic matter content, and low ammonia concentrations. The Ames test results demonstrate that all extracts from ozonated water have mutagenic activity; however, the 18 raw groundwater samples had no mutagenicity. The Microtox test results also show that the ozonated water samples were highly toxic. Generally, both bromide and DOC content promoted the formation of ozonation by-products and mutagenicity. Controlling of bromide and DOC concentrations is an effective method of reducing potential by-product formation and eliminating mutagenicity problems associated with groundwater ozonation.

Ozonation of Algae and Odor Causing Substances in Eutrophic Waters

Consumers generally concern taste and odor in drinking water. In the Southern Taiwan, more than 5,000,000 people are suffered from earth/musty odor in drinking water, especially in the summer. Thus, ozonation of geosmin (GSM), 2-methylisoborneol (2-MIB), and 2-furfural (2-FF) in eutrophic surface waters has been studied in the present work. Experimentally, it was found that the water contained high dissolved organic carbon (DOC), humic substances, and specific ultraviolet absorbance (SUVA) resulting the highly ozone (O3) demand. The natural organic matters (NOM) in the waters had a significant effect on the ozonation of GSM, 2-MIB and 2-FF. Their destruction rates were increased with high contents of aromatics, phenolics, and SUVAs. In addition, during ozonation of raw waters, O3 and OH· played an important role in destruction of algae cells and caused excretion of extracellular organic matter (EOM) to the bulk phase.

Biological toxicity of groundwater in a seashore area: Causal analysis and its spatial pollutant pattern

To ensure the safety of groundwater usage in a seashore area where seawater incursion and unexpected leakage are taking place, this paper utilizes the Microtox test to quantify the biological toxicity of groundwater and proposes an integrated data analysis procedure based on hierarchical cluster analysis (HCA) and principal component analysis (PCA) for determining the key environmental factors that may result in the biological toxicity, together with the spatial risk pattern associated with groundwater usage. For these reasons, this study selects the coastal area of Taichung city in Central Taiwan as an example and implements a monitoring program with 40 samples. The results indicate that the concentration of total arsenic in the coastal areas is about 0.23-270.4 μg L(-1), which is obviously higher than the interior of Taichung city. Moreover, the seawater incursion and organic pollution in the study area may be the key factors resulting in the incubation of toxic substances. The results also indicate that As(3+) is the main contributor to biological toxicity compared to other disinfection by-products. With the help of the visualized spatial pollutants pattern of groundwater, an advanced water quality control plan can be made.

Causal relationships among biological toxicity, geochemical conditions and derived DBPs in groundwater

Groundwater is indispensable water resource in coastal areas of Taiwan and is typically used following simple disinfection. Disinfection by-products (DBP), which are hazardous materials that are biologically toxic, are commonly produced. To elucidate the effect of environmental factors on the formulation of DBPs and arsenic species, and the effect of these factors on the bio-toxicity, data from a one-year monitoring program that was performed in a coastal area of central Taiwan were analyzed using the multivariate statistical method of redundancy analysis (RDA). The results reveal that the dominant DBP for trihalomethanes (THMs) was CHCl3 and for haloacetic acids (HAAs) was CHClBr2COOH (BDCAA). The formation of these compounds was most affected by the concentrations of humic substances and Br(-). As(5+) ions are abundant in the area close to the seashore and are the main source of biological toxicity. Cl(-), Br(-) and As(5+) concentrations were strongly correlated with biological toxicity as they promoted the formation of DBP. A geographic information system (GIS) and the above results revealed that the area near the seashore is rich in Br(-) wherever high As(5+) concentration and bio-toxicity are detected.

Atmospheric-particulates-bound mercury Hg(p) study at five characteristic sampling sites in Taiwan.

The main purpose for this study is to observe the seasonal and month variations for particulates-bound mercury Hg(p) in total suspended particulates (TSP) concentration, dry deposition at five characteristic sampling sites during years of 2009–2010 in central Taiwan. The results show that the highest and lowest monthly average particulates-bound mercury Hg(p) concentrations in TSP were occurred in Dec. and Oct. at Gao-mei (wetland), Chang-hua (downtown) and He-mei (residential) sampling site. In addition, the results show that the highest and lowest monthly average particulates-bound mercury Hg(p) dry deposition was occurred in Feb. and Oct. at Quan-xing (industrial) sampling site. This study reflected that the mean highest particulates-bound mercury Hg(p) concentrations in TSP and mean highest particulates-bound mercury Hg(p) dry deposition were occurred at Gao-mei (wetland) and Quan-xing (industrial). However, the mean lowest particulates-bound mercury Hg(p) concentrations in TSP and mean lowest particulates-bound mercury Hg(p) dry deposition were also occurred at Gao-mei (wetland). Regarding seasonal variation, the order of mean-particulates-bound mercury Hg(p) concentrations in TSP in winter and spring were Gao-mei (wetland) > Quan-xing (industrial) > Bei-shi (suburban/coastal) > Chang-hua (downtown) > He-mei (residential). Finally, the order of mean-particulates-bound mercury Hg(p) dry deposition in fall, spring and summer were Quan-xing (industrial) > Bei-shi (suburban/coastal) > Chang-hua (downtown) > He-mei (residential) > Gao-mei (wetland).

Effects of extracellular polymeric substances on the bioaccumulation of mercury and its toxicity toward the cyanobacterium Microcystis aeruginosa

This investigation examines how extracellular polymeric substances (EPSs) and environmental factors affect the bioaccumulation and toxicity of inorganic mercury (+2 oxidation state, Hg(II)) using a culture of Microcystis aeruginosa, which dominates eutrophic reservoir populations. The identified EPSs were classified as carbohydrates and proteins. Evaluation of the bioaccumulation of Hg(II) in cells by multiple regression analysis reveals that the concentration of EPSs in filtrate, the initial concentration of Hg(II) in medium, and the culture age significantly affected the amount of Hg(II) accumulated. Composition profiles revealed that the concentrations of soluble carbohydrates were significantly higher in Hg(II)-accumulated cells than in the control ones. Preliminary results based on scanning electron microscopic (SEM) map investigations suggest that most of the Hg(II) was accumulated in the cytoplasm (intracellular). Additionally, the effective concentrations (EC50) of Hg(II) that inhibit the growth of M. aeruginosa were 38.6 μg L−1 in the logarithmic phase and 17.5 μg L−1 in the stationary phase. As expected, the production of more EPSs in the logarithmic phase typically implies higher EC50 values because EPSs may be regarded as a protective barrier of cells against an external Hg(II) load, enabling them to be less influenced by Hg(II).

Toxicity and Bioaccumulation of Monomethylmercury in Freshwater Cyanobacteria: Oscillatoria tenuisa and Microcystis aeruginosa

This study investigated the toxicity and bioaccumulation of monomethylmercury (MMHg) using two freshwater cyanobacteria— Oscillatoria tenuisa and Microcystis aeruginosa—that were isolated from a eutrophic reservoir. Tested concentrations were 1, 10, 50, and 250 μg L−1 of MMHg. The MMHg uptake depended on the phases of growth, period of exposure, and initial concentration of MMHg to which the cyanobacteria were exposed. The growth rate during the logarithmic phase was 0.17 day−1 for O. tenuisa, and 0.05 day−1 for M. aeruginosa in 250 μg L−1 of MMHg. These rates were a factor of 3.5–6 lower than that in the original medium without exposure to MMHg. The accumulation of MMHg by cyanobacteria increased rapidly within 4 weeks from the initial value of 1.2 × 10−4 – 1.6 × 10−4 ng cell−1 on sampling day 2 in the lag phase to 0.92 × 10−3 – 7.5 × 10−2 ng cell−1 on sampling day 28 during the stationary phase. The uptake rate of MMHg in the logarithmic phase cultures greatly exceeded that in the stationary cultures. The accumulation of MMHg by cyanobacteria depended on extracellular organic matter (EOM). Linear correlation analysis indicated a significant and negative correlation between the amount of bioaccumulation of MMHg in cyanobacterial cells and EOM concentration in suspension. Additionally, the effective concentrations (EC) of MMHg for inhibiting the growth of the two cyanobacterial species at 96 h (96 h EC50) were determined to be 340 μg L−1 for M. aeruginosa and 568 μg L−1 for O. tenuisa. The no observed effect concentrations (NOEC) for the two species were 64 μg L−1 and 115 μg L−1, respectively. Preliminary results that were based on SEM-map studies suggest that most of the MMHg accumulated in the cytoplasm (intercellular) of M. aeruginosa.

Evaluation of disinfection by-products formation during ozonation of bromide-containing groundwater.

Abstract Ozonation of natural waters containing bromide ion leads to the formation of inorganic bromate and many organic by-products, only a few of which have been identified. The object of this article is to identify primary ozone disinfection by-products (DBPs) and to ascertain the effects of bromide (Br−) concentration, pH, natural organic material (NOM) characteristics, ozone dosage, and other water quality parameters on their formation in ozonated waters derive from seven groundwaters. The results of this study show that bromate formation is favored at high pH, high initial bromide concentrations, and high ozone dosage, but low dissolved organic carbon (DOC), and ammonia levels. On the other hand, organic by-products were favored at low pH, high bromide levels, and high O3/DOC ratios. In general, bromoform (CHBr3) and aldehydes concentration first increased, then diminished, as the dosage of ozone was increased. Ammonia appears to reduce both bromate and bromoform. Additional brominated organic by-products produced via ozonation of a variety of groundwaters in this study were monobromoacetic acid (MBAA), dibromoacetic acid (DBAA), 2,4-dibromophenol (2,4-DBP), dibromoacetonitrile (DBAN). The levels of these by-products are affected by the water quality characteristics. The background organic nitrogen (organic-N) content of the different water sources may be correlated with amounts of DBAN formed. It was also found that the characteristic of organic precursors have significant influences on brominated organic by-products formation. Humic acid demonstrated the highest CHBr3, DBAA, and 2,4-DBP formation, whereas hydrophilic neutral produced less CHBr3 and 2,4-DBP than the rest of the organic fractions but produced the highest amount of DBAN.