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This study describes a comparative degradation of various chlorophenols by electro-Fenton method. Chloride released and reaction intermediate products were determined by ionic chromatography (IC) and gas chromatography/mass spectrometry (GC/MS). Using pentachlorophenol (PCP) as the model compound, we investigated the effects of cell voltage, electrolyte concentration and pH to optimize the degradation conditions. It was noted that the addition of small quantities of Fe3+ or Fe2+ significantly accelerated the degradation rate. Under the optimal conditions, electro-Fenton method was used to treat various chlorophenols including PCP, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and their mixture aqueous solutions. Their pseudo first-order degradation rate constants at the first stages were calculated and compared, which gave the following sequence: 2,4-DCP>2,4,6-TCP>PCP>4-CP. The relationship between the chlorine content and degradation rate was discussed and compared with other advanced oxidation processes. Finally, we proposed the degradation pathways of different chlorophenols.
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PMID:Comparison treatment of various chlorophenols by electro-Fenton method: relationship between chlorine content and degradation. 1572 32

This study evaluates the application of Wet Peroxide Oxidation (WPO) for the treatment of solutions containing 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP). These compounds are of special interest due to their high toxicity and low biodegradability. WPO is included in the Advanced Oxidation Processes, which are technologies based on an initial formation of hydroxyl radicals that further oxidize the organic matter. The influence of some operating conditions such as temperature, dosage of hydrogen peroxide and initial concentration of the chlorophenols was studied in absence of a catalyst. The results of this study prove that 4-CP and 2,4-DCP can be completely removed from wastewaters by means of WPO. Total Organic Carbon (TOC) and 4-CP removals of 72.3% and 100%, respectively, were achieved working at 100 degrees C with 2.5 mL of H(2)O(2) and an initial concentration of 500 ppm of 4-CP after 90 min of reaction. Under the same conditions but with an initial concentration of 500 ppm of 2,4-DCP a TOC removal of 59% and a complete removal of the target compound were achieved.
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PMID:Wet peroxide oxidation of chlorophenols. 1574 24

Effect of a biogenic substrate (peptone) concentration on the performance of sequencing batch reactor (SBR) treating 220 mg/l 4-chlorophenol (4-CP) and 110 mg/l 2,4-dichlorophenol (2,4-DCP) mixtures was investigated. In this context, peptone concentration was gradually decreased from 300 mg/l to null in which chlorophenols were fed to the reactor as sole carbon and energy sources. By this way, the effect of peptone concentration on observed yield coefficient (Y), biomass concentration, chlorophenols and COD removal performances were investigated. Decreasing peptone concentration accompanied with lower biomass concentration led to increase in peak chlorophenol and COD concentrations within the reactor during each SBR cycle. This, in turn, caused noteworthy declines in the removal rates as chlorophenol degradations followed Haldane substrate inhibition model. Also, increased peak chlorophenol concentrations led to the accumulation of 5-chloro-2-hydroxymuconic semialdehyde (CHMS), which is -meta cleavage product of 4-CP. Despite the decreased removal rates, complete chlorophenols and CHMS degradation, in addition to high COD removal efficiencies (>90%), were observed for all studied conditions, even chlorophenols were added as sole carbon and energy sources. Another significant point is that 2,4-DCP at slightly elevated concentrations (>20 mg/l) within the reactor caused a strong competitive inhibition on 4-CP degradation. In SBR, feeding the influent to the reactor within a certain period (i.e. filling period) provided dilution of coming wastewater, which decreased the chlorophenols concentrations to which microorganisms were exposed. Therefore, use of SBR may help to avoid both self and competitive inhibitions in the treatment of 4-CP and 2,4-DCP mixture especially in the presence high biogenic substrate concentrations. In addition, isolation and identification studies have indicated that Pseudomonas sp. and Pseudomonas stutzeri were dominant species in the acclimated mixed culture.
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PMID:Effect of biogenic substrate concentration on the performance of sequencing batch reactor treating 4-CP and 2,4-DCP mixtures. 1615 49

Aquatic plants take up and sequester organic contaminants such as chlorophenols through incorporation in cell wall materials and storage in vacuoles. The ultimate fate of plant-sequestered chlorophenols, however, remains unclear. This research investigated 2,4-dichlorophenol (2,4-DCP) sequestration by the aquatic plant Lemna minor and evaluated contaminant release and bioavailability after plant death and cellular disruption. 14C-labeled 2,4-DCP was used to establish that contaminant removed from the aqueous phase was retained internal to L. minor. An assay with Desulfitobacterium sp. strain Viet1 was used to assess the readily bioavailable fraction of plant-sequestered 2,4-DCP and plant metabolites of 2,4-DCP. In plant-free systems, strain Viet1 dechlorinated 2,4-DCP to stoichiometric amounts of 4-chlorophenol (4-CP) as a stable and quantifiable end product. Anaerobic microcosms containing inactivated L. minor, which had accumulated 3.8 micromol of 2,4-DCP equivalents/g of plant material (fresh weight) during a preceding aerobic exposure, were inoculated with strain Viet1. After 118 d of incubation with strain Viet1, 43.5% (+/-1.4%) of the contaminant was recovered as 4-CP, indicating a large portion of plant-sequestered 2,4-DCP was bioavailable for dechlorination by strain Viet1. In contrast, 4-CP formation was not observed in autoclaved microcosms, and only 26.1% (+/-1.0%) of plant-sequestered 2,4-DCP was recovered in the aqueous phase. These findings demonstrate contaminant cycling between plants and microorganisms, and emphasize that understanding the mechanisms and pathways of contaminant sequestration by plants is critical for predicting long-term contaminant fate.
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PMID:Activity of Desulfitobacterium sp. strain Viet1 demonstrates bioavailability of 2,4-dichlorophenol previously sequestered by the aquatic plant Lemna minor. 1646 99

Phenoxyalkanoic compounds are used worldwide as herbicides. Cupriavidus necator JMP134(pJP4) catabolizes 2,4-dichlorophenoxyacetate (2,4-D) and 4-chloro-2-methylphenoxyacetate (MCPA), using tfd functions carried on plasmid pJP4. TfdA cleaves the ether bonds of these herbicides to produce 2,4-dichlorophenol (2,4-DCP) and 4-chloro-2-methylphenol (MCP), respectively. These intermediates can be degraded by two chlorophenol hydroxylases encoded by the tfdB(I) and tfdB(II) genes to produce the respective chlorocatechols. We studied the specific contribution of each of the TfdB enzymes to the 2,4-D/MCPA degradation pathway. To accomplish this, the tfdB(I) and tfdB(II) genes were independently inactivated, and growth on each chlorophenoxyacetate and total chlorophenol hydroxylase activity were measured for the mutant strains. The phenotype of these mutants shows that both TfdB enzymes are used for growth on 2,4-D or MCPA but that TfdB(I) contributes to a significantly higher extent than TfdB(II). Both enzymes showed similar specificity profiles, with 2,4-DCP, MCP, and 4-chlorophenol being the best substrates. An accumulation of chlorophenol was found to inhibit chlorophenoxyacetate degradation, and inactivation of the tfdB genes enhanced the toxic effect of 2,4-DCP on C. necator cells. Furthermore, increased chlorophenol production by overexpression of TfdA also had a negative effect on 2,4-D degradation by C. necator JMP134 and by a different host, Burkholderia xenovorans LB400, harboring plasmid pJP4. The results of this work indicate that codification and expression of the two tfdB genes in pJP4 are important to avoid toxic accumulations of chlorophenols during phenoxyacetic acid degradation and that a balance between chlorophenol-producing and chlorophenol-consuming reactions is necessary for growth on these compounds.
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PMID:Chlorophenol hydroxylases encoded by plasmid pJP4 differentially contribute to chlorophenoxyacetic acid degradation. 1659 83

This paper investigated the biodegradation kinetics of 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) separately in batch reactors and mixed in sequencing batch reactors (SBRs). Batch reactor experiments showed that both 4-CP and 2,4-DCP began to inhibit their own degradation at 53 and 25 mg l(-1), respectively, and that the Haldane equation gave a good fit to the experimental data because r(2) values were higher than 0.98. The maximum specific degradation rates (q(m)) were 130.3 and 112.4 mg g(-1) h for 4-CP and 2,4-DCP, respectively. The values of the half saturation (K(s)) and self-inhibition constants (K(i)) were 34.98 and 79.74 mg l(-1) for 4-CP, and 13.77 and 44.46 mg l(-1) for 2,4-DCP, respectively. The SBR was fed with a mixture of 220 mg l(-1) of 4-CP, 110 mg l(-1) of 2,4-DCP, and 300 mg l(-1) of peptone as biogenic substrate at varying feeding periods (0-8h) to evaluate the effect of feeding time on the performance of the SBR. During SBR operation, in addition to self-inhibition, 4-CP degradation was strongly and competitively inhibited by 2,4-DCP. The inhibitory effects were particularly pronounced during short feeding periods because of higher chlorophenol peak concentrations in the reactor. The competitive inhibition constant (K(ii)) of 2,4-DCP on 4-CP degradation was 0.17 mg l(-1) when the reactor was fed instantaneously (0 h feeding). During longer feedings, increased removal/loading rates led to lower chlorophenol peak concentrations at the end of feeding. Therefore, in multi-substrate systems feeding time plus reaction time should be determined based on both degradation kinetics and substrate interaction. During degradation, the meta cleavage of 4-chlorocatechol resulted in accumulation of a yellowish color because of the formation of 5-chloro-2-hydroxymuconic semialdehyde (CHMS), which was further metabolized. Isolation and enrichment of the chlorophenols-degrading culture suggested Pseudomonas sp. and Pseudomonas stutzeri to be the dominant species.
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PMID:Effect of feeding time on the performance of a sequencing batch reactor treating a mixture of 4-CP and 2,4-DCP. 1684 2

The biodegradation kinetics of 2,4-dichlorophenol (2,4-DCP) by culture (Culture M) acclimated to mixture of 4-chlorophenol (4-CP) and 2,4-DCP and the culture (Culture 4) acclimated to 4-CP only were investigated in aerobic batch reactors. Also, pure strains isolated from mixed cultures were searched for their ability towards the biodegradation of 2,4-DCP. Culture 4 was able to completely degrade 2,4-DCP up to 80 mg/L within 30 h and removal efficiency dropped to 21% upon increasing initial concentration to 108.8 mg/L. When the Culture M was used, complete degradation of 2,4-DCP in the range of 12.5-104.4 mg/L was attained. A linear relationship between time required for complete degradation and initial 2,4-DCP concentrations was observed for both mixed cultures. It was observed that the Haldane equation can be used to predict specific degradation rate (SDR) (R(2)>0.99) as a function of initial 2,4-DCP concentrations and it adequately describes 2,4-DCP concentration profiles. Both of the mixed cultures settled well, which is important to maintain good removal efficiency for longer periods of time for real full-scale applications. Although the pure strains isolated from mixed cultures were found to have higher SDR of 2,4-DCP compared to mixed cultures, they did not settle well under quiescent conditions.
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PMID:Biodegradation kinetics of 2,4-dichlorophenol by acclimated mixed cultures. 1697 34

Two instantaneously fed sequencing batch reactors (SBRs), one receiving 4-chlorophenol (4-CP) (SBR4) only and one receiving mixture of 4-CP and 2,4-dichlorophenol (2,4-DCP) (SBRM), were operated with increasing chlorophenols concentrations in the feed. Complete degradation of chlorophenols and high-Chemical oxygen demand (COD) removal efficiencies were observed throughout the reactors operation. Only a fraction of biomass (competent biomass) was thought to be responsible for the degradation of chlorophenols due to required unique metabolic pathways. Haldane model developed based on competent biomass concentration fitted reasonably well to the experimental data at different feed chlorophenols concentrations. The presence of 2,4-DCP competitively inhibited 4-CP degradation and its degradation began only after complete removal of 2,4-DCP. Based on the experimental results, the 4-CP degrader's fraction in SBRM was estimated to be higher than that in SBR4 since 2,4-DCP degraders were also capable of degrading 4-CP due to similarity in the degradation pathways of both compounds.
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PMID:Modeling chlorophenols degradation in sequencing batch reactors with instantaneous feed-effect of 2,4-DCP presence on 4-CP degradation kinetics. 1709 47

The 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM][PF6]) ionic liquid was immobilized in the pores of a polypropylene hollow fiber for hollow fiber-protected liquid-phase microextraction. Analytes including 4-chlorophenol (4-CP), 3-chorophenol (3-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) were extracted into this ionic liquid membrane, and back extracted into 10microL sodium hydroxide acceptor solution in the lumen of the hollow fiber. Then, the acceptor solution was withdrawn into the high-performance liquid chromatography (HPLC) microsyringe connected to the hollow fiber, and directly injected into the HPLC system for analysis. Some parameters that might affect the extraction efficiency were optimized, and low detection limits (0.5microgL(-1) for 4-CP, 3-CP, DCP and 1.0microgL(-1) for TCP) were obtained. Good repeatability was achieved because of the stability of the hollow fiber-supported ionic liquid membrane. The proposed procedure was applied for direct determination of the four chlorophenols in some real water samples including groundwater, river water, wastewater and tap water. All of the four chlorophenols in these water samples were under the limits of determination, and the recoveries were in the range of 70.0-95.7% at 5microgL(-1) spiked level.
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PMID:Direct determination of chlorophenols in environmental water samples by hollow fiber supported ionic liquid membrane extraction coupled with high-performance liquid chromatography. 1711 89

An efficient sequential, biological and photocatalytic treatment to reduce the pollutant levels in wastewater due to the bleaching process during paper production is reported. For a biological pre-treatment, 800 ml of non-sterilized effluent was inoculated with Trametes versicolor immobilized in polyurethane foam, with 25 g l(-1) glucose, 6.75 mM CuSO(4), and 0.22 mM MnSO(4) added, and cultured at 25 degrees C with an air flow of 800 ml min(-1) for 8d. The fungus did not inhibit growth of the heterotropic populations of the effluent. After 4d of culture, the chemical oxygen demand (COD) reduction and colour removal (CR) were 82% and 80%, respectively, with laccase (LAC) and manganese peroxidase (MnP) activities of 345 U l(-1) and 78 U l(-1), respectively. The COD reduction and CR correlated positively (p<0.0001) with LAC and MnP activities. Chlorophenol removal was 99% of pentachlorophenol, 99% of 2,3,4,6-tetrachlorophenol (2,3,4,6-TCP), 98% of 3,4-dichlorophenol (3,4-DCP) and 77% of 4-chlorophenol (4-CP), while 2,4,5-trichlorophenol (2,4,5-TCP) increased to 0.2 mg l(-1). The pre-treated effluent was then exposed to a photocatalytic treatment. The treatment with photolysis resulted in 9% CR and 46% COD reduction, 42% CR and 60% COD reduction by photocatalysis, and 62% CR and 85% COD reduction by heterogeneous photocatalysis with the system TiO(2)/Ru(x)Se(y) (Fig. 4). With this treatment the bacterial and fungal populations also decreased by 5 logarithmic units with respect to the biological treatment alone (Fig. 5). The total sequential treatment resulted in a 92% CR (from 5800 UC), 97% COD reduction (from 59 g l(-1)) and 99% chlorophenol removal at 96 h and 20 min.
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PMID:Sequential treatment via Trametes versicolor and UV/TiO2/Ru(x)Se(y) to reduce contaminants in waste water resulting from the bleaching process during paper production. 1712 83


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