Reductive dechlorination of chlorobenzene in supercritical water catalyzed by Fe/ZrO<Subscript>2</Subscript>

Reductive dechlorination of chlorobenzene by Fe/ZrO₂ in supercritical water was investigated. The effects of the operation conditions were studied. The dechlorination of chlorobenzene obeyed pseudo-first-order kinetics models. In supercritical water, the rate constant increases more rapidly with temperature than those in subcritical water. The results showed that the rate-determining step of dechlorination in subcritical water is diffusion; whereas the rate-determining of dechlorination in supercritical water is chemical reaction. The reaction mechanism in subcritical water might involve with an ionic mechanism; whereas the reaction mechanism in supercritical water might involve with a homolytic reaction.     

Color removal efficiency of dyes using nanozerovalent iron treatment

In this study, zerovalent iron nanoparticles (Fe⁰) were synthesized by chemical reduction method using ferric chloride hexahydrate (FeCl₃?·?6H₂O) as a starting material. Sodium borohydride (NaBH₄) was used as a reducer. The synthesized nanozerovalent iron (NZVI) was separated using magnets. The X-ray diffraction pattern of iron (Fe) nanoparticles showed that the presence of intensive diffraction peak at 2θ value of 45.33° from the lattice plane of face-centered cubic Fe unequivocally indicates that the particles are made of pure Fe. The size of the synthesized NZVI was found to be 16.64?nm. The scanning electron micrograph revealed that the particles have a hexagonal and spherical shape in nature. EDX showed the surface atomic distribution and chemical composition of NZVI. The decolorization efficiency rose with increasing concentration of nanoparticles as well as with time. Maximal color removal efficiency was 90.72% when using 0.5?g/100?mL Fe nanoparticle for acridine orange. Data revealed that the function of NZVI on color removal efficiency was statistically significant. The correlation coefficient between NZVI concentration and time showed a strong negative correlation for dyes used in the experiment.     

Efficient DDT and trichlorophenol detoxification using NaBH4 and Devarda alloy

DDT—1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane—is a pesticide that has been widely used to control insects in agriculture. TCP—2,4,6-trichlorophenol—has been used in pesticide formulations as a preservative, disinfectant and antiseptic. Detoxification of DDT and TCP is very difficult due to their stable chemical structure. Here, a mixture of NaBH₄ and Devarda alloy was applied for the first time to detoxify DDT and TCP. Results show 94 % dechlorination of DDT at 100 °C and 97 % dechlorination of TCP at 80 °C. The presence of diphenyl ethane suggests the complete dechlorination of DDT. The formation of benzene suggests a strong reduction. The method is efficient, cost-effective and may be applied at the industrial-level.     

PVC的热解脱氯动力学分析

采用动态热重法对PVC热解脱氯反应动力学进行了研究,对不同升温速率下TG曲线采用下同方法分析,计算出反应速率常数、反应级数、活化能等脱氯反应动力学参数,并推断出反应机制,分析结果表明,PVC热解存在两个阶段,氯原子主要在250℃-300℃之间以HCl的形式释放,且反应为一级反应。     

Catalytic decomposition of polychlorinated biphenyls (PCBs)

In this study, polychlorinated biphenyls (PCBs) were decomposed by low‐temperature heat treatment with metallic catalyst, and with metallic catalyst and a hydrogen source. Of the catalysts used, iron (Fe) was the most active catalyst for the decomposition of PCBs, and the decomposition was due to dechlorination. The addition of hydrogen sources accelerated the decomposition of PCBs in the presence of catalyst. Surface analysis of the catalyst using X‐ray photoelectron spectroscopy (XPS) suggested that the emitted chlorine was presumed to form metal chloride. The reactions of each homolog can be expressed by a successive first‐order reaction model. This means that a substituted chlorine is successively detached during this reaction. The overall decomposition rate in this reaction system was controlled by that of the lower chlorinated homologs. The decomposition rates with Fe and NaBH₄ for the lower chlorinated homologs were about 10 times as fast as the rates with only Fe.     

Accumulation,tissue distribution and elimination of 203HgCl2 and CH3 203HgCl in the tissues of the American oyster Crassostrea virginica

Oysters (Crassostrea virginica) were exposed for 3 days to mercury-203 labeled HgCl₂ or CH₃HgCl added directly to artificial seawater or added preconcentrated on the marine diatom Phaeodactylum tricornutum. The concentration of mercury in 5 tissues was measured for 45 days after mercury was removed from the ambient water. At the beginning of the depuration period, the highest concentrations of mercury in tissues were attained in: gill>digestive system>mantle>gonad>muscle in oysters exposed to water containing mercury; and in digestive system>gill>mantle> gonad>muscle in oysters fed labeled algae. This same distribution pattern is seen for both chemical forms of mercury. Although the initial pattern of accumulation was identical for both mercury compounds within each exposure group, the fate of the accumulated mercury was very different after 45-days depuration. In oysters accumulating mercury directly from seawater, inorganic mercury residues rapidly declined in gill and digestive tissue, but were slowly reduced in mantle, gonadal, and muscle tissue. This pattern was duplicated by oysters exposed to methyl mercuric chloride in seawater except that gonadal and muscle residues greatly increased during depuration. In oysters ingesting labeled P. tricornutum cells, mercuric chloride and methyl mercuric chloride residues rapidly declined in gill and digestive tissue, remained constant in the mantle, but sharply increased in gonadal and muscle tissue during depuration.     

Toxaphen in der Umwelt

Toxaphene is a mixture of more than 200 polychlorinated C₁₀-terpenes. Due to its persistence and long-range transport, it is distributed all over the world. Many of the components are very stable under environmental conditions, while others are easily degraded by UV-light or microorganisms. The main conversion pathway is reductive dechlorination and dehydrochlorination; oxidative degradation possibly occurs only after previous dechlorination. Accumulation especially in the aquatic environment has led in many cases to high residue levels in fish, marine mammals, and sea birds of the northern hemispere. Toxaphene is mutagenic in the Ames test and of high toxicity for fish, but few data are available on the toxicity of single components or their mode of action.     

Detection of polychlorinated biphenyls employing chemical dechlorination followed by biphenyl whole cell sensing system

Polychlorinated biphenyls (PCBs) are a mixture of 209 individual chlorinated compounds commonly known as PCB congeners. These compounds are hydrophobic and are persistent in the environment. Their use was banned in the US a few decades ago because of harmful health effects. Therefore, detection of PCBs in environmental samples is increasingly important. To that end, we have developed a two-step simple and sensitive method for the detection of total PCBs. Specifically, our method involves dechlorination of PCBs to biphenyl followed by detection of biphenyl using a whole cell sensing system as the detection system. The whole cell sensing system consists of cells of the strain Pseudomonas pseudoalcaligenes KF707 harboring plasmid pSD7000. Plasmid pSD7000 contains the gene of lacZ, a reporter protein under the control of the bph operon. The detection is achieved through the emission of light afforded by the expression of reporter protein triggered by the presence of biphenyl. Due to the fact that this operon is activated only by few PCB congeners, a chemical dechlorination method was employed to convert all PCBs to biphenyl, and thus all the PCBs present in a given sample are able to be detected. The results showed that PCB congeners were rapidly (30?min) and efficiently (>98.5%) dechlorinated to biphenyl using a Mg/K₂PdCl₆ catalyst, and the biphenyl could be subsequently quantified using the whole cell sensing system. This hybrid analytical method that combines classical dechlorination with novel biosensing methods may find applications in the on-site monitoring of PCBs contamination levels.     

Effects of arsenic on osmoregulation in the tilapia Oreochromis mossambicus reared in seawater

The effects of arsenic (As₂O₃) on plasma osmolarity, Na and K concentrations, the activity of gill Na–K-ATPase, and on the ultrastructure of gill chloride cells were compared between seawater tilapia (Oreochromis mossambicus) and freshwater tilapia in the Institute of Zoology, Academia Sinica, between 1989 and 1991. Arsenic was found to be more lethal in seawater tilapia [96 h LC₅₀ (median lethal concentration): 26.5 ppm] than in freshwater ones (71.7 ppm). No significant effect was found on plasma ion concentrations and osmolarity, enzyme activity or the ultrastructure of chloride cells in freshwater tilapia after 96 h exposure to 70 ppm arsenic. In contrast, 96 h exposure to 15 ppm arsenic caused evident effects in seawater tilapia: an increase in plasma osmolarity and activity of gill Na–K-ATPase, as well as better development of the chloride cell tubular system. These data suggest that the lethal effect of arsenic may be partially attributed to a hydromineral disturbance in seawater tilapia, but in freshwater tilapia arsenic perhaps causes destruction in some physiological mechanisms other than osmoregulation. The activation of gill Na–K-ATPase and chloride cells in seawater tilapia appears to indicate an adaptation in the osmoregulatory mechanism to arsenic exposure, i.e., to enhance secreting ions or arsenic in the gills.     

High dechlorination of PCBs catalysed by carbon under mild conditions

This article reports high dechlorination of toxic polychlorinated biphenyls (PCBs) under mild conditions. PCBs are priority pollutants acting as endocrine disruptors, human carcinogens and environmental estrogens. Previous remediation methods involving high temperature and pressure have drawbacks such as high cost, de novo dioxins synthesis and difficult recovery of vaporized PCBs. On the other hand, dechlorination methods using mild conditions show the problem of catalyst deactivation. Here, activated carbon was used for the first time as catalyst to dechlorinate 2,4,5 trichlorobiphenyl. High dechlorination, of 87%, was achieved under mild conditions. 2,4,5 trichlorobiphenyl was treated at 40–150°C with calcium hydroxide, sodium hydroxide and sulfur in mixed water and organic solvents. Dechlorination products were biphenyl, orthohydroxy biphenyls, 2,4 dihydroxy biphenyls and biphenyl-2-thiol. Dichlorobiphenyl and orthochlorobiphenyls were found in trace quantities. We found that carbon particles catalysed dechlorination by substitution reactions and suppressed further chlorination. Dechlorination at biphenyl ortho position was preceded by substitution reaction by hydroxyl and thiol ions. Moreover, in the absence of carbon, dechlorination was lower and substituted products were not observed. These findings may be applied at industrial scale to remediate PCB-contaminated waste.     

Degradation of pentachlorophenol in a contaminated soil suspension using hybrid catalysts prepared via urea�Cformaldehyde polycondensation between iron(III)-tetrakis(p-hydroxyphenyl)porphyrin and humic acid

Hybrid catalysts were synthesized by attaching iron(III)-tetrakis(p-hydroxyphenyl)porphyrin (FeTPP(OH)₄) to humic acid (HA) via urea–formaldehyde polycondensation. FTIR spectra of the prepared catalysts indicated that the catalysts prepared via urea–formaldehyde polycondensation contained cross-links between the phenolic groups of FeTPP(OH)₄ and HA, which contains aliphatic amine functional groups. The prepared catalysts were examined for their ability to catalyze the oxidative degradation of pentachlorophenol (PCP) in a contaminated soil suspension. The levels of PCP degradation and dechlorination for the hybrid catalysts were significantly higher than those for the non-modified catalyst, FeTPP(OH)₄.     

Optimizing the configuration of a clearwell by integrating pilot and full-scale tracer testing

In this paper, the main factors impacting the plug flow pattern of a clearwell were investigated by integrating pilot-scale, full-scale clearwell tracer testing and computational fluid dynamics (CFD) simulation. It was found that pilot tracer testing, full-scale tracer testing and CFD simulation all demonstrated that the correlation between the ratio of t ₁₀/T and L/W can be approximately expressed by: t ₁₀/T = 0.189 4ln(L/W)-0.049 4. This study confirmed that the installation of baffles within clearwells is an efficient way to optimize their configuration. In addition, the inlet velocity has a minimal contribution to the ratio of t ₁₀/T. However, the ratio of turning channel width to channel width (d/W) significantly contributes to the ratio of t ₁₀/T. The optimal ratio of d/W is 0.8–1.2 for maintaining better plug flow pattern. The number of turning channels is one of the main factors that impact the ratio of t ₁₀/T. When increasing the number of turning channels, a lower ratio of t ₁₀/T is obtained.     

Bioaccumulation of lead and the influence of chelating agents in Catla catla fingerlings

Lead is a widespread element and one of the persistent and cumulative pollutants of the environment. The present study deals with the bioaccumulation of lead and the influence of chelating agents, meso 2,3-dimercaptosuccinic acid (DMSA), D-Penicillamine and CaNa₂EDTA in reducing the concentration of lead on the selected organs of Catla catla fingerlings for both acute and chronic exposures by using ICP-AES. It is inferred from the present findings that there was a correlation between environmental conditions and the heavy metal contents of the fish. The highest concentration of lead is found in kidney tissues and the lowest in muscle tissues. The accumulation pattern of lead in the selected organs of Catla catla is: kidney > liver > gill > brain > muscle. Also, it has been found that the treatment of chelating agents, DMSA, D-Penicillamine and CaNa₂EDTA reduces the concentration of lead significantly for both acute and chronic exposures. The results also show that DMSA is the most effective chelator of lead in reducing the body burden of C. catla fingerlings. The observed data further indicate that C. catla could be suitable for monitoring organisms to study the bioavailability of water-bound metals in freshwater habitats.     

Iron-carbon composite microspheres prepared through a facile aerosol-based process for the simultaneous adsorption and reduction of chlorinated hydrocarbons

Iron-carbon (Fe-C) composite microspheres prepared through a facile aerosol-based process are effective remediation agents for the simultaneous adsorption and reduction of chlorinated hydrocarbons. Complete dechlorination was achieved for the class of chlorinated ethenes that include tetrachloroethylene (PCE), trichloroethylene (TCE), cis- and trans-1,2-dicloroethylene (c-DCE, t-DCE), 1,1-dichloroethylene (1,1-DCE) and, vinyl chloride (VC). The Fe-C particles potentially provides multi-functionality with requisite characteristics of adsorption, reaction, and transport for the effective in situ remediation of chlorinated hydrocarbons. The carbon support immobilizes the ferromagnetic iron nanoparticles onto its surface, thereby inhibiting aggregation. The adsorptive nature of the carbon support prevents the release of toxic intermediates such as the dichloroethylenes and vinyl chloride. The adsorption of chlorinated ethenes on the Fe-C composites is higher (>80%) than that of humic acid (<35%) and comparable to adsorption on commercial activated carbons (>90%). The aerosol-based process is an efficient method to prepare adsorptive-reactive composite particles in the optimal size range for transport through the porous media and as effective targeted delivery agents for the in situ remediation of soil and groundwater contaminants.     

Intertype mark correlation function: A new tool for the analysis of species interactions

The spatial pattern of the different species in complex ecosystems reflects the underlying ecological processes. In this paper a second order moment function is proposed and tested to analyse the spatial distribution of a mark, which could be a tree characteristic such as diameter or height, between two different types of points, which could be two different tree species. The proposed function was a conditional density function based on the intertype K_rs(d) function, incorporating as test function the correlation of the marks between pairs composed of points of different types. The results obtained in simulated and real plots prove that the function is capable of revealing the scale at which spatial correlation of the mark between two types of points exists. The proposed function allows the spatial association between individuals of different species at different life stages to be identified. This analysis may reveal information on species ecology and interspecific interactions in forest ecosystems.     

Distribution,fate and persistence of organochlorine compounds formed during production of bleached pulp

The processes governing distribution of a xenobiotic compound discharged initially into the environment are discussed, and attention is drawn to (a) binding to organic matter in the sediment phase which affects both persistence and toxicity to biota and (b) the role of atmospheric transport for compounds of low water solubility and high vapour pressure. Important limitations in the use of sum parameters such as EOCI are pointed out. The important distinction between biodegradation and biotransformation is pointed out, and significant experimental determinants noted. Pathways for the aerobic metabolism of chlorophenolic compounds are discussed, and attention is drawn to the role of O‐methylation as an environmentally significant alternative to biodegradation. Evidence for the biodegradation of chlorinated aliphatic acids and hydrocarbons under both aerobic and anaerobic conditions is presented. Anaerobic metabolism of chlorophenolic compounds is discussed with respect to (a) de‐O‐methylation of chloroguaiacols, (b) dechlorination of chlorocatechols and (c) reduction of chlorovanillins. It is emphasized that current evidence provides a complex metabolic picture, and that only partial dechlorination may occur. Brief attention is given to the important issue of the persistence of chlorolignin, and attention drawn to technical issues which render this problem difficult of access by traditional procedures. Biohalogenation—particularly by fungi—is noted, though its quantitative contribution cannot be estimated at the moment. A number of important unresolved issues are underscored: (a) the problem of determining rates of microbial reactions which may be translated to environmental situations, (b) the cardinal role not only of the number of chlorine atoms in an aromatic compound but also the substitution pattern and (c) limitations in current understanding of the role of anaerobic bacteria in bringing about biodegradation and biotransformation.     

Degradation of chlorinated phenols by nanoscale zero-valent iron

Chlorophenols (CPs), as important contaminants in groundwater, are toxic and difficult to biodegrade. Recently nanoscale zero-valent iron received a great deal of attention because of its excellent performance in treating recalcitrant compounds. In this study, nanoscale zero-valent iron particles were prepared using chemical reduction, and the reductive transformations of three kinds of chlorinated phenols (2-CP, 3-CP, and 4-CP) by nanoscale zero-valent iron under different conditions were investigated. The transformation process of the CPs was shown to be dechlorination first, then cleavage of the benzene ring. The removal efficiency of the CPs varied as follows: 2-CP > 3-CP > 4-CP. The reactivity of CPs was associated with their energy of lowest unoccupied molecular orbit (E _LUMO). With the increase in initial concentrations of CPs, removal efficiency decreased a little. But the quantities of CPs reduced increased evidently. Temperature had influence on not only the removal efficiency, but also the transformation pathway. At higher temperatures, dechlorination occurred prior to benzene ring cleavage. At lower temperatures, however, the oxidation product was formed more easily.     

Decomposition of perfluorooctanoic acid by microwaveactivated persulfate: Effects of temperature, pH, and chloride ions

Microwave-hydrothermal treatment of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water with persulfate (S₂O ₈ ^2? ) has been found effective. However, applications of this process to effectively remediate PFOA pollution require a better understanding on free-radical scavenging reactions that also take place. The objectives of this study were to investigate the effects of pH (pH = 2.5, 6.6, 8.8, and 10.5), chloride concentrations (0.01?C0.15 mol·L^?1), and temperature (60°C, 90°C, and 130°C) on persulfate oxidation of PFOA under microwave irradiation. Maximum PFOA degradation occurred at pH 2.5, while little or no degradation at pH 10.5. Lowering system pH resulted in an increase in PFOA degradation rate. Both high pH and chloride concentrations would result in more scavenging of sulfate free radicals and slow down PFOA degradation. When chloride concentrations were less than 0.04 mol·L^?1 at 90°C and 0.06 mol·L^?1 at 60°C, presence of chloride ions had insignificant impacts on PFOA degradation. However, beyond these concentration levels, PFOA degradation rates reduced significantly with an increase in chloride concentrations, especially under the higher temperature.     

Direct production of hydroxymethylfurfural from raw grape berry biomass using ionic liquids and metal chlorides

We report for the first time the direct conversion of raw grape berry biomass to hydroxymethylfurfural (HMF) using ionic liquid solvents with metal chloride catalysts. Exploiting raw plant biomass as a biorefinery feedstock is innovative for sustainable chemical industry. The use of the raw biomass to synthesize compounds can indeed lead to less energy consumption and less CO₂ emissions. Using raw plant biomass skips pretreatment steps that are required to produce biomaterials such as carbohydrates or cellulosic biomass. Here, grape berry biomass was used as a raw chemical feedstock for the production of hydroxymethylfurfural, a key platform intermediate for syntheses of future renewable biofuels. We examined 3 ionic liquid solvents, 3 reaction temperatures, 5 chloride catalysts, and 5 concentrations of HCl. We found an increasing HMF yields depending on reaction conditions. 1-octyl-3-methylimidazolium chloride was most effective for HMF synthesis. Addition of HCl or metal chlorides alone showed little improvement. The highest HMF yield of about 100 mg HMF per mL of grape biomass extract was obtained using 0.3 M HCl, [OMIM]Cl, and CrCl₂ at 100°C for 3 h. Our study provides a model system of sustainable production of valuable compounds from raw plant biomass.     

NOx- und NO2-Konzentrationen

It has been confirmed that the NO_x-concentration in air is highest over industrial areas and that it decreases by more than 75%, parallel to traffic density, over urban areas as related to forested areas. A significant correlation excists between NO₂-concentration and the parameters of “traffic density,” followed by “road density” and “number of inhabitants/km²” in urban areas. No positive correlation was found with the number of “registered cars” and the parameters of “land use”. In forested areas, the traffic density correlated with the NO₂-concentration, but the correlation was not significant. The other parameters had no positive correlation with NO₂-concentration. In forest, urban- and industrial-areas, the NO_x-concentration in the air had a fairly constant ratio to traffic density.