Degradation Of Monochlorophenols Research Articles

Assessment of the generation of chlorinated byproducts upon Fenton-like oxidation of chlorophenols at different conditions

Homogeneous Fenton-like (H 2O 2/Fe 3+) oxidation proved to be highly efficient in the degradation of monochlorophenols but some important issues need to be considered depending on the operating conditions. When using the stoichiometric amount of H 2O 2 and a dose of Fe 3+ in the range of 10–20 mg/L, complete breakdown of 4-CP up to CO 2 and short-chain acids was achieved. Nevertheless, when substoichiometric amounts of H 2O 2 or lower concentrations of iron were used, significant differences between the TOC measured and the calculated from the identified species were found. These differences were attributed to condensation byproducts, including chlorinated species, formed by oxidative coupling reactions. PCBs, dioxins and dichlorodiphenyl ethers were identified. A solid residue was also formed consisting mainly in carbon, oxygen and chlorine including also Fe. The occurrence of these highly toxic species must be carefully considered in the application of Fenton oxidation to wastewaters containing chlorophenols. The possibility of reducing costs by lowering the H 2O 2 dose below the stoichiometric one needs to tke this into account.

Substrate-dependent autoaggregation of Pseudomonas putida CP1 during the degradation of mono-chlorophenols and phenol.

A bacterium, CP1, identified as Pseudomonas putida strain, was investigated for its ability to grow on and degrade mono-chlorophenols and phenols as sole carbon sources in aerobic shaking batch culture. The organism degraded up to 1.56 mM 2- and 3-chlorophenol, 2.34 mM 4-chlorophenol and 8.5 mM phenol using an ortho-cleavage pathway. P. putida CP1, acclimated to degrade 2-chlorophenol, was capable of 3-chlorocatechol degradation, while P. putida, acclimated to 4-chlorophenol degradation, degraded 4-chlorocatechol. Growth of P. putida CP1 on higher concentrations of the mono-chlorophenols, >or=1.56 mM 4-chlorophenol and >or=0.78 mM 2- and 3-chlorophenol, resulted in decreases in cell biomass despite metabolism of the substrates, and the formation of large aggregates of cells in the culture medium. Increases in cell biomass with no clumping of the cells resulted from growth of P. putida CP1 on phenol or on lower concentrations of mono-chlorophenol. Bacterial adherence to hydrocarbons (BATH) assays showed cells grown on the higher concentrations of mono-chlorophenol to be more hydrophobic than those grown on phenol and lower concentrations of mono-chlorophenol. The results suggested that increased hydrophobicity and autoaggregation of P. putida CP1 were a response to toxicity of the added substrates.

Substrate-dependent autoaggregation of Pseudomonas putida CP1 during the degradation of mono-chlorophenols and phenol

Substrate-dependent autoaggregation of Pseudomonas putida CP1 during the degradation of mono-chlorophenols and phenol

Degradation of mono-chlorophenols by a mixed microbial community via a meta- cleavage pathway.

A mixed microbial community, specially designed to degrade a wide range of substituted aromatic compounds, was examined for its ability to degrade mono-chlorophenols as sole carbon source in aerobic batch cultures. The mixed culture degraded 2-, 3-, and 4-chlorophenol (1.56 mM) via a meta- cleavage pathway. During the degradation of 2- and 3-chlorophenol by the mixed culture, 3-chlorocatechol production was observed. Further metabolism was toxic to cells as it led to inactivation of the catechol 2,3-dioxygenase enzyme upon meta- cleavage of 3-chlorocatechol resulting in incomplete degradation. Inactivation of the meta- cleavage enzyme led to an accumulation of brown coloured polymers, which interfered with the measurement of cell growth using optical density. Degradation of 4-chlorophenol by the mixed culture led to an accumulation of 5-chloro-2-hydroxymuconic semialdehyde, the meta- cleavage product of 4-chlorocatechol. The accumulation of this compound did not interfere with the measurement of cell growth using optical density. 5-chloro-2-hydroxymuconic semialdehyde was further metabolized by the mixed culture with a stoichiometric release of chloride, indicating complete degradation of 4-chlorophenol by the mixed culture via a meta- cleavage pathway.

Degradation of monochlorophenols by γ-irradiation

The degradation of aqueous 5 × 10 −4 mol dm −3 2-, 3- and 4-chlorophenol (2-CIP, 3-CIP, 4-CIP) under reducing and oxidizing conditions has been studied by steady state γ-radiolysis. The reaction with e aq − leads to reductive dechlorination which equals the degradation of the chlorophenols. Solely phenol is the major organic compound formed. In N 2O saturated solutions the dehalogenation is much less effective. In the case of 4-CIP 40% and in that of 2- and 3-CIP only 20% of the decomposed substrates are resulting in chlorine free organic compounds. From these pyrocatechol for 2-CIP and hydroquinone for 4-CIP could be identified in minor amounts. Main products are the hydroxylated substrates originating from the primarily formed ortho- and para OH-adducts. These are for 2-CIP: chlorohydroquinone and 3-chlorocatechol, for 3-CIP: chlorohydroquinone, 3- and 4-chlorocatechol and for 4-CIP: 4-chlorocatechol. In the presence of oxygen, where the OH-adducts are converted into peroxyl radicals, the degradation yield of the substrates corresponds to that of OH radicals up to doses of 0.5 kGy. The dechlorination process in this dose range is 50% for 4-CIP, and 33% for 2- and 3-CIP. The position of chlorine on the aromatic ring strongly influences the dehalogenation and degradation process. A pronounced dependency of the dose/yield curves on the oxygen concentration was observed. This indicates that for an efficient degradation process of chlorophenols oxygen supply is necessary during irradiation.

Degradation of Monochlorophenols by <i>Pseudomonas putida</i> CP1 in the Presence of Growth Supplements

Influence of readily degradable additional sources of carbon and nitrogen on the degradation of monochlorophenols by Pseudomonas putida CP1 was investigated. The organism grew on all three isomers of monochlorophenols when supplied as the sole source of carbon and energy. Low concentrations (0.01 to 0.5%, w/v) of yeast extract enhanced degradation of monochlorophenols. The order in terms of rate of removal of monochlorophenols was 4-chlorophenol > 2-chlorophenol > 3-chlorophenol, both in the presence and absence of the growth supplements. The rate of removal of monochlorophenols was highest when carbon:nitrogen (C:N) ratio maintained at optimum level (3:1) with monochlorophenols and growth substrates. The organism clumped when grown in the presence of monochlorophenols alone. The degree of clumping decreased with the addition of growth supplements. Keywords: Biodegradation, Growth supplement, Monochlorophenol, Pseudomonas putida CP1DOI: http://dx.doi.org/10.3329/bjm.v24i2.1254 Â Bangladesh J Microbiol, Volume 24, Number 2, December 2007, pp 115-118 Â Â