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PubMed2003

[Kinetics of P-chlorophenol wastewater treatment by UV/H2O2 oxidation].

The photodegradation of p-cholorophenol in a hydrogen peroxide-aided photolysis process was investigated. The reaction was influenced by the original concentration of p-chlorophenol and H2O2 addition and carrier gas. With the aid of dioxygen, the removal of phenol and CODCr were reached about 96% and 50% respectively if the original concentration of H2O2 added was only half of stoichiometric calculation. A pseudo-first order kinetic model was adopted to represent the reaction.

Chlorophenols↗
PubMed2004

Modeling of the acclimation/deacclimation process of a mixed culture degrading 4-chlorophenol.

The variation of concentration of the toxic substrate has a negative effect on the sludge activity. Although this loss of activity of the microorganisms under toxic starvation has been reported, this variable is not taken into account in the operation of biological wastewater treatment plants. In order to monitor and control the biological plant with a certain confidence it is necessary to consider the acclimation and deacclimation processes to avoid the reactor malfunctioning, resulting in loss of efficiency or in false data acquisition during monitoring. This paper proposes a model for the acclimation/deacclimation process. The experiments have been done in a sequencing batch reactor during the 4-chlorophenol degradation. The basic idea of the model is to consider the variation of the kinetic parameters of the Haldane law in terms of the acclimation and deacclimation state. The idea is discussed, and the results obtained are presented.

Bioreactors↗
PubMed2004

Degradation of 4-chlorophenol mediated by Fe(III)-NTA in homogeneous and heterogeneous systems.

In this work, the comparison of 4-chlorophenol (4-CP) degradation by two different AOT processes has been performed: a) a homogeneous system with Fe(III)-NTA (1:1 complex), b) a TiO2/Fe(III)-NTA heterogeneous system. In both cases, NTA appears to play a positive role in the photochemical reaction. In the homogeneous system, the iron salt is the only absorbing species and is proved to be able to photoinduce 4-CP degradation ([4-CP] = 0.1-0.2 mM, [FeNTA] = 0.3-0.9 mM, pH 4, lambda = 365 nm). The progress of the reaction was positively affected by the FeNTA concentration, and the reaction kept going even after the total disappearance of FeNTA. However, 4-CP complete degradation requires the presence of oxygen, otherwise the reaction stops. In the heterogeneous system ([4-CP] = 2.0 mM, [FeNTA] = 1.0-2.0 mM, [TiO2] = 0.1 and 1.0 g L(-1), pH 3, lambda = 300-400 nm), an important effect of the complex on the degradation extent and on the initial reaction rate can be seen, which overcomes the effect of non-complexed Fe(III). This behaviour is more important at the highest TiO2 concentration.

Chlorophenols↗
PubMed2004

Aerobic biodegradation of 3-chlorophenol in a sequencing batch reactor: effect of cometabolism.

The aim of the present study was to investigate how phenol modifies, through cometabolism, the biodegrading capability of 3-chlorophenol (3-CP) in a sequencing batch reactor seeded with a mixed culture obtained from a domestic sewage treatment plant. Two laboratory-scale SBRs, one fed 3-CP only and the other fed 3-CP and phenol in the same concentration, were seeded with the partially acclimated biomass. The removal capability in both reactors was measured for progressive increases in the feed organic loading. Cometabolism enhanced biodegradation of 3-CP by reducing both the initial lag period and the time required for the complete removal. 700 mg/L 3-CP was demonstrated to be the highest concentration, which could be completely degraded during the active phase (fill plus react) either in the presence or absence of phenol as the growth substrate even though the lag period was shorter when phenol was present. The operating strategy required modification for the complete removal of 800 mg/L 3-CP. An increase in the phenol to 3-CP ratio did, however, improve 3-CP degradation rate.

Animals↗
PubMed2004

Variation of the microbial activity during the acclimation phase of a SBR system degrading 4-chlorophenol.

The variation of microbial activity during acclimation to 4-chlorophenol (4CP) in an aerobic automated sequencing batch reactor was studied. The results show a reduction in degradation time as the acclimation process occurred. During acclimation for an initial concentration of 50 mg 4CP/L, degradation time was reduced from 40 h to 50 min after 10 cycles. In the case of an initial concentration of 100 mg/L, degradation time was reduced from 52 h to 1.16 h, also after 10 cycles. Doubling the initial concentration of a previously acclimated sludge produces only a slight increase in degradation time. It was found that as acclimation took place, the affinity of the consortia to biodegrade the toxic increased, whereas the ability to biodegrade acetate decreased. The evolution of the substrate uptake rate over time during the acclimation period was highly correlated with an exponential relationship. It was also observed that acclimation decreased both the production of a toxic metabolite and the sludge volumetric index.

Acclimatization↗
PubMed2005

Mechanisms of dioxin formation from the high-temperature oxidation of 2-chlorophenol.

The homogeneous, gas-phase oxidative thermal degradation of 2-chlorophenol was studied in a 1 cm i.d., fused silica flow reactor at a concentration of 88 ppm, reaction time of 2.0 s, over a temperature range of 300 to 1000 degrees C. Observed products in order of yield were as follows: 4,6-dichlorodibenzofuran (4,6-DCDF) > dibenzo-p-dioxin (DD) > 1-monochlorodibenzo-p-dioxin (1-MCDD), 4-chlorodibenzofuran (4-MCDF), dibenzofuran (DF), naphthalene, chloronaphthalene, 2,4-dichlorophenol, 2,6-dichlorophenol, phenol, chlorobenzene, and benzene. In contrast to pyrolysis, 4,6-DCDF is the major product rather than DD, and 1-MCDD and naphthalene are formed at temperatures as low as 400 degrees C. Under oxidative conditions, .OH and Cl. are the major carriers, which favors 4,6-DCDF formation over DD or 1-MCDD through abstraction of H. through diketo- and ether- intermediates. It is proposed that below 500 degrees C, unimolecular tautomerization/HCI elimination and CO elimination/isomerization reactions result in the formation of 1-MCDD and naphthalene, respectively.

Chlorophenols↗
PubMed2005

[Study on dechlorination of p-chlorophenol by Ni/Fe bimetallic particles].

Dechlorination property of p-chlorophenol (p-CP) by Ni/Fe bimetallic particles was studied in this work. The experimental results show that adsorbed hydrogen atom is the main reductive agent for dechlorination of p-CP and chemical reaction at the surface of catalyst is the rate-determing step in this process. The catalyst with mass ratio of 2.96% Ni had the largest specific surface area and also had the highest dechlorination efficiencies (64% in 90 min) under the same conditions. The apparent kinetics of p-CP dechlorination by Ni/Fe was the first order reaction and apparent rate constant (kappa) was proportional to the specific surface of catalyst. The apparent rate constant per specific surface area (kappa') was also calculated (7.61 x 10(-4) min(-1) m(-2)). Temperature was also an important parameter in this system. The dechlorination efficiency was proportional to temperature when it is below 43 degrees C, when temperature exceeded 43 degrees C, increasing temperature had inverse effect on dechlorination efficiency.

Chlorophenols↗
PubMedDate not supplied

[Heterogeneity of Rhodococcus opacus 1CP as a response to stress induced by chlorophenols].

Dissociation of Rhodococcus opacus 1CP during culturing in different media (containing phenol and its monochlorinated derivatives as the sole source of carbon and energy) was studied. Three variants of strain 1CP (S1, S2, and R) differing in the morphology of cells and colonies, lipid composition, and manner of growth on phenol and monochlorophenols were isolated. It was shown that 2- and 4-chlorophenols were most actively degraded by the smooth (S) forms of the culture, and that the rough (R) form predominated when the culture was grown in a rich medium. The S forms differed from the R forms of the strain by an increased content of cardiolipin, fatty acids, and phosphatidylethanolamine.

Acetates↗
PubMed2004

Removal of phenol and chlorophenols from water by coir pith carbon: equilibrium and rate studies.

Batch mode studies were conducted to study the removal of phenol, 2,4,6-Trichlorophenol (TCP) and Pentachlorophenol (PCP) from aqueous solution on coir pith carbon by adsorption process under varying experimental conditions such as agitation time, adsorbent dose, pH and temperature. Kinetics of adsorption obeyed second order rate equation and the rate constant was found to be in the range 0.0098-0.0672, 0.0949-0.8801 and 0.172-0.305 g/mg/min for phenol, TCP and PCP respectively. Equilibrium adsorption data follow Langmuir isotherm for phenol and PCP and the adsorption capacities were found to be 48.3 mg and 3.7 mg/g, respectively. For TCP, adsorption followed Freundlich isotherm only. Acidic pH was favorable for the adsorption of all the chlorophenols. Studies on pH effect and desorption show that chemisorption seems to play a major rule in the adsorption process. The positive values of H0 24.99, 18.69, and 8.907 kJ/mol for phenol, TCP and PCP respectively, confirm the endothermic nature of adsorption.

Adsorption↗
PubMedDate not supplied

Phenoxyacetic acid herbicides and chlorophenols and the etiology of lymphoma and soft-tissue neoplasms.

The phenoxyacetic acid herbicides and the chlorophenols are compounds of economic importance. The herbicide 2,4-D is widely used in agriculture, industry, and the home. Recently, concern has arisen over their safety as a result of studies linking these compounds with soft-tissue sarcomas and non-Hodgkin's lymphomas. We reviewed the available literature in order to advise a provincial government regulatory body and investigated methodologic issues by examining the pattern of reported cases in Alberta. We conclude that, taking into account the serious limitations on methodology in the available data, the evidence for a causal association is strongest for non-Hodgkin's lymphomas and probably reflects either a weak effect or, possibly, a confounding exposure associated with the use of 2,4-D. Given the worst-case assumptions, however, the potency of 2,4-D as a carcinogen is probably weak. Its intrinsic toxicity is less than that of alternative herbicides and the hazard posed by its use is probably much less than either the use of chemical alternatives or manual cleaning of vegetation, which carry a high risk of occupational injuries.

Chlorophenols↗
PubMedDate not supplied

Chemical derivatization analysis of pesticide residues. VIII. Analysis of 15 chlorophenols in natural water by in situ acetylation.

A rapid analytical method is presented for quantitative analysis of 15 chlorophenols in natural waters by in situ acetylation. In the presence of KHCO3, phenols in water are acetylated by acetic anhydride directly without pre-extraction. The resultant acetates are extracted by petroleum ether and analyzed by electron capture gas chromatography. The investigation to optimize the conditions for in situ acetylation of these phenols is also described. This method has been validated and shown to be applicable over a range from 100 to 0.01 ppb with a 1 L water sample.

Acetylation↗
PubMed1995

Soft tissue sarcoma and non-Hodgkin's lymphoma in workers exposed to phenoxy herbicides, chlorophenols, and dioxins: two nested case-control studies.

We examined the effect of exposure to chemicals present in the production and spraying of phenoxy herbicides or chlorophenols in two nested case-control studies of soft tissue sarcoma and non-Hodgkin's lymphoma. Eleven sarcoma and 32 lymphoma cases occurring within an international cohort were matched for age, sex, and country of residence with 55 and 158 controls, respectively. Exposures to 21 chemicals or mixtures were estimated by three industrial hygienists who were blind to the subject's case-control status. Excess risk of soft tissue sarcoma was associated with exposure to any phenoxy herbicide [odds ratio (OR) = 10.3; 95% confidence interval (CI) = 1.2-91] and to each of the three major classes of phenoxy herbicides (2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, and 4-chloro-2-methylphenoxyacetic acid), to any polychlorinated dibenzodioxin or furan (OR = 5.6; 95% CI = 1.1-28), and to 2,3,7,8-tetrachlorodibenzo-p-dioxin (OR = 5.2; 95% CI = 0.85-32). Sarcoma risk was not associated with exposure to raw materials or other process chemicals. In the non-Hodgkin's lymphoma study, associations were generally weaker than those found in the study on sarcoma. These findings indicate that workers exposed to phenoxy herbicides and their contaminants are at a higher risk of soft tissue sarcoma.

Case-Control Studies↗
PubMed1993

[Reductive dechlorination of chlorophenols by an anaerobic mixed culture].

In this study, we investigated the potential for reductive dechlorination of chlorophenols by municipal sewage sludge acclimated to 2,4-dichlorophenol (2,4-DCP) and 3,4-dichlorophenol (3,4-DCP). The optimal temperature and pH for dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) were 30 degrees C and 7.2. Dechlorination of 2,4,6-TCP was inhibited by sulfate, nitrate, or ferric (III), but was increased by manganese (IV) except that product of 2,4-DCP was accumulated. Organic substrates such as pyruvate or acetate did not influence dechlorination of 2,4,6-TCP, but increased dechlorination of 2,4-DCP; nevertheless lactate showed no influence on dechlorination. When glucose was added as substrate, only 20% of 2,4,6-TCP dechlorination was found. Addition of methanogenesis inhibitor 2-bromoethane sulfonate did not influence dechlorination, but addition of eubacteria inhibitor vancomycin showed no dechlorination activity at the first few days, and finally complete transformation and accumulation of 2,4-DCP occurred. Because mixed culture was from Di-Hwa Wastewater Treatment Plant, adding the same water as culture medium was found to increase the dechlorination of 2,4,6-TCP and its product 2,4-DCP. Dechlorination by adding wastewater of Petroleum Corporation was also increased, especially for 2,4-DCP product, but only 7% of 2,4,6-TCP dechlorination was found after incubation with Hou-Chin river water for 14 days.

Bacteria, Anaerobic↗
PubMed1998

[Evaluation of the effects of chlorophenol-free wood antiseptics in experimental animals].

The authors report on creation of domestic chlorophenol-free preservatives for wood (EOK, K-12, Katan) in Arkhangelsk Research Institute. Application of those chemicals is cheaper than that of foreign analogs. Toxicity of the preservatives was evaluated according to morphologic and functional changes in various organs and systems of experimental animals which faced long exposure to the preservatives. The experiments proved K-12 to be the most pathogenic among others. EOK preservative fails to induce severe pathologic changes in experimental animals, demonstrated no cumulation and allergy. Katan takes intermediate place between those two.

Animals↗
PubMed1998

Degradation of 2-chlorophenol and formation of 2-chloro-1,4-benzoquinone by mycelia and cell-free crude culture liquids of Trametes versicolor in relation to extracellular laccase activity.

The white-rot fungus Trametes versicolor was used to study the influence of extracellular laccase activity on the degradation of 2-chlorophenol (2-CP) and the formation of metabolites under conditions, characterized by the absence of other phenol-oxidizing enzymes. 2-CP enhanced the production of extracellular laccase by fungal mycelia. The formation of the metabolite 2-chloro-1,4-benzoquinone (2-CIBQ) was found to be correlated with extracellular laccase activity. In cell-free crude culture liquids laccase was responsible for the oxidation of 2-CP. In contrast to this, the disappearance of 2-CP caused by the entire organism did not correlate with extracellular laccase activity. The primary oxidative step during the degradation of this compound can thus only partially be attributed to extracellular laccase; indicating the involvement of cell-bound processes.

Basidiomycota↗
PubMedDate not supplied

Toxicological profile for o-benzyl-p-chlorophenol.

As part of a health-hazard survey on the health risk of hospital cleaning workers from exposure to Lyorthol, a hazard assessment of o-benzo-p-chlorophenol, one of the constituents of Lyorthol, has been prepared. In this paper, the physical and chemical characteristics, kinetics and effects of o-benzochlorophenol are described and discussed, and an overall, summarizing hazard evaluation is presented.

Administration, Oral↗
PubMed2004

Aryl cation and carbene intermediates in the photodehalogenation of chlorophenols.

The photochemistry of 2,6-dimethyl-4-chlorophenol (6) has been studied in methanol and trifluoroethanol (TFE) through product studies and transient absorption spectroscopy. Chloride loss from triplet 6 gave triplet hydroxyphenyl cation 14, which equilibrated with triplet oxocyclohexadienylydene 15 within a few tens of nanoseconds; the cation can, however, be selectively trapped by allyltrimethylsilane (k(ad) = 10(8)-10(9) m(-1) s(-1)) to give a phenonium ion and the allylated phenol. In neat alcohols, 14 and 15 are reduced through different mechanisms, namely by hydrogen transfer through radical cation 17 and via phenoxyl radical 16, respectively. The mechanistic rationalization has been substantiated by the parallel study of an O-silylated derivative. The work shows that the chemistry of the highly (but selectively) reactive phenyl cation 14 can not only be discriminated from that of the likewise highly reactive carbene 15, but also exploited for synthetically useful reactions, as in this case with alkenes. Photolysis of electron-donating substituted halobenzenes may be the method of choice for the mild generation of some classes of phenyl cations.

Journal Article↗
PubMed2005

The photochemistry of 4-chlorophenol in water revisited: the effect of cyclodextrins on cation and carbene reactions.

The photochemistry of 4-chlorophenol (1) in water and in the presence of cyclodextrins has been studied by means of steady-state and time-resolved experiments. These have shown that 1 undergoes photoheterolysis of the C--Cl bond in the triplet state to yield the 4-hydroxyphenyl cation (3)2 in equilibrium with 4-oxocyclohexa-2,5-dienylidene, (3)3. These triplet intermediates scarcely react with a n nucleophile, such as water, nor abstract hydrogen from this solvent, thus they are long-lived (approximately 1 micros). Specific trapping of both intermediates has been achieved. The cation adds to 2-propenol, k(add) approximately 1.3 x 10(8) m(-1) s(-1), to form the long-lived phenonium ion 11 (with lambda(max) = 290 nm), which then converts to 3-(4-hydroxyphenyl)propane-1,2-diol (10). Carbene (3)3 is trapped by oxygen to give benzoquinone and is reduced by D-glucose (k(q) = 8.5 x 10(6) m(-1) s(-1)) to give the phenoxyl radical (8) and phenol (9). Cyclodextrins have been found to trap the intermediates much more efficiently (k(q) = 9.4 x 10(8) m(-1) s(-1) with beta-CD), which indicates that inclusion is involved. Ground state 1 forms inclusion complexes with 1:1 stoichiometry and association constants of 140 and 300 M(-1) with alpha- and beta-CD, respectively. Complexation does not change the efficiency or the mode of photofragmentation of 1; however, it does influence the course of the reaction because the major portion of the intermediates are reduced to phenol within the cavity (k'(red)> or = 5 x 10(7) s(-1)) either via a radical 8 or via a radical cation 9(+)(.). Under these conditions, neither 2-propenol nor oxygen trap the intermediates to a significant extent.

Journal Article↗