4-chlorophenol degradation

Some other studies showed that the combination of the three polymorphs with reduced crystallite size and high surface area can lead to the best photocatalysts for 4-chlorophenol degradation [37], or that particles in the dimension range 25-40 nm give the best performances [38]. Therefore, many elements contribute to the final photocatalytic activity and sometimes the increased contribution of one parameter can compensate for the decrease of another one. For example, better photocatalytic activity can be obtained even if the surface area decreases, with a concomitant increase in the crystallinity of the sample, which finally results in a higher number of electron-hole pairs formed on the surface by UV illumination and in their increased lifetime (slower recombination) [39]. Better crystallinity can be obtained with the use of ionic liquids during the synthesis [39], with a consequent increase of activity. 

Figure 3 Major pathways of 4-chlorophenol degradation as derived from product analysis. (From Refs. 58 and 59.)...

Gray, K. A. Stafford, U. Probing photocatalytic reactions in semiconductor systems Study of the chemical intermediates in 4-chlorophenol degradation by a variety of methods, Res. Chem. Intermed. 1994, 20, 835. 

Figure 2B also shows that the first-order rate constants of 4-chlorophenol degradation are inversely proportional to the initial 4-chlorophenol concentration, whereas the initial rate constants are proportional to the initial 4-chlo-rophenol concentration. When the reciprocals of the initial rate constants are... 

Jernberg C, Jansson JK (2002) Impact of 4-chlorophenol contamination and/or inoculation with the 4-chlorophenol-degrading strain, Arthrobacter chlorophenolicus A6L, on soil bacterial community structure. FEMS Microbiol Ecol 42 387-397... 

Carberry photoreactor Immobilized Low-pressure mercury (355 nm) 4-Chlorophenol degradation [166]... 

Considerable interest has been expressed in the chlorophenol-degrading organism Mycobacterium chlorophenolicum (R. chlorophenolicus) (Apajalahti et al. 1986), partly motivated by its potential for application to bioremediation of chlorophenol-contaminated industrial sites (Haggblom and Valo 1995). 

Haggblom, M.M. and Young, L.Y. Chlorophenol degradation coupled with sulfate reduction, Appl Environ. Microbiol, 56(ll) 3255-3260, 1990. 

Figure 8.2. Pathways for chlorophenol degradation under aerobic (A,B) and anaerobic (C) conditions.

Table 8.5. Examples of kinetic parameters for chlorophenol degradation modeled by Monod or Haldane (Kl involved) equations... 

Table 8.9. Examples of chlorophenol degradation by sediment cultures... 

Briglia, M. (1995). Chlorophenol-degrading actinomycetes molecular ecology and bioremediation properties. Ph.D. Thesis, Department of Applied Chemistry and Microbiology, University of Helsinki, Helsinki, Finland. 

Haggblom, M. M. Young, L. Y. (1990). Chlorophenol degradation coupled to sulfate reduction. Applied and Environmental Microbiology, 56, 3255-60. 

In another work [148], mineralization of chlorophenols was followed by measurement of the chloride ion concentration in water during 03, 03/UV, and UV/H202 treatment. Compared to ozonation results, these authors did not find any improvement of chlorophenol degradation rate when UV light was used in combination with ozone. The authors also determined the toxicity of aqueous solutions of treated chlorophenols with the Daphnia magna 24-hr test. After 90-95% elimination of CPs they did not find any negative effect of ozonation by-products on the aquatic organism. 

Ferrihydrite catalysis of hydroxyl radical formation from peroxide has also shown experimental results consistent with a surface reaction [57]. The yield of hydroxyl radical formation was lower for ferrihydrite than for dissolved iron, resulting in a higher peroxide demand to degrade a given amount of pollutant. As mentioned above, although ferrihydrite exhibited a faster rate of peroxide decomposition than goethite or hematite, the rate of 2-chlorophenol degradation with these catalysts was fastest for hematite [55], In other studies, quinoline oxidation by peroxide was not observed when ferrihydrite was used as catalyst [53]. 

Weavers LK, Malmstadt N, Hoffmann MR. Kinetics and mechanism of penta-chlorophenol degradation by sonication, ozonation and sonolytic ozonation. Environ Sci Technol 2000 34 1280-1285. 

Chlorophenol degradation proceeds via dechlorination (removal of Cl-groups) with hydroxylation (addition of OFl-groups) at the dechlorinated sites. The microbes are effectively manipulating the molecule to make it susceptible to degradation by cleavage of the benzene ring. 

Haggblom, M.M., L.J. Nohynek, N.J. Palleroni, K. Kronqvist, E.-L. Nurmiaho-Lassila, M.S. Salkinoja-Salonen, S. Klatte, and R.M. Kroppenstedt. 1994. Transfer of poly-chlorophenol-degrading Rhodococcus chlorophenolicus Apajalahti et al. 1986 to the genus Mycobacterium as Mycobacterium chlorophenolicum comb. nov. Int. J. Syst. Bacteriol. 44 485—493. 

Leung KT, Watt A, Lee H, Trevors JT (1997) Quantification detection of penta-chlorophenol-degrading Sphingomonas sp. UG30 in soil by a most-probable-number polymerase chain reaction protocol. J Microbiol Method 31 59-66... 

In 0.1 wt% slurries, the average interparticle distance is so small that the measured rate of TCE conversion is much less than the potential mass transfer limit [117]. In contrast, with the catalyst immobilized on walls of tubes of several mm diameter, mass transfer influence may exist, and has been demonstrated with data for salicylic acid conversion in a coiled tube [68,116]. A clear variation of reaction rate with flow rate exists, and an analysis [117] suggested that the data are very strongly mass transfer influenced. A similar influence of fluid flow rate on the first order rate constant has been noted in chlorophenol degradation on photocatalyst-coated glass beads [36]. 

Anodic oxidation was also shown to be a feasible technique for chlorophenol degradation (55). The mechanisms for this process is not well understood. It is hypothesized that chlorophenol radical cations are first formed and subsequently deprotonated. The product undergoes further oxidation to a benzoquinone derivative and ring-opening to acids, such as muconic, naleic, and oxalic and finally to CO2 (36-38). Just like cathodic reduction, the efficiency of anodic oxidation of chlorophenol depends on the material of the electrodes. Generally, oxide-based anodes perform better than metals as they are less prone to the formation of oligomers, which cause the inactivation of the electrodes (35M39). 

Shchukin D, Poznyak S, Kulak A, Pichat P (2004) Ti02-In203 photocatalysts preparation, characterisations and activity for 2-chlorophenol degradation in water. J Photochem... 

Wastewater. Phenol is a toxic poUutant to the waterways and has an acute toxicity (- 5 m g/L) to fish. Chlorination of water gives chlorophenols, which impart objectionable odor and taste at 0.01 mg/L. Biochemical degradation is most frequently used to treat wastewater containing phenol. Primary activated sludge, along with secondary biological treatment, reduces phenol content to below 0.1 mg/L (69). 

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