Degradation Of M-cresol Research Articles

Treatment of phenolics containing synthetic wastewater in an internal loop airlift bioreactor (ILALR) using indigenous mixed strain of Pseudomonas sp. under continuous mode of operation

The scope of this study is to evaluate the performance of internal loop airlift bioreactor (ILALR) in treating synthetic wastewater containing phenol and m-cresol, in single and multi component systems. The microbe utilized in the process was an indigenous mixed strain of Pseudomonas sp. isolated from a wastewater treatment plant. The reactor was operated at both lower and higher hydraulic retention times (HRTs) i.e., 4.1 and 8.3 h, respectively, by providing an inlet feed flow rate of 5 and 10 mL/min. Shock loading experiments were also performed up to a maximum concentration of 800 mg/L for phenol at 8.3 h HRT and 500 mg/L for m-cresol at 4.1 h HRT. The study showed complete degradation of both phenol and m-cresol, when they were degraded individually at a HRT of 8.3 h. Experiments with both phenol and m-cresol present as mixtures were performed based on the 2 2 full factorial design of experiments.

Selectivity in photocatalysis by particulate semiconductors

AbstractTiO2, Fe2O3, CuO, ZnO, ZnS, Nb2O5, MoO3, CdO, CdS, Sb2O3, CeO2, HgO, Pb2O3, PbO2 and Bi2O3 microparticles exhibit band gap excitation with UV-A light but they are selective to photodegrade phenols. While TiO2 anatase and ZnO photocatalyze the degradation of phenol, o-aminophenol, m-aminophenol, p-aminophenol, o-chlorophenol, m-chlorophenol, p-chlorophenol, o-nitrophenol, p-nitrophenol, o-cresol, m-cresol, p-cresol, catechol, resorcinol and quinol, MoO3 does not photodegrade any of the fifteen phenols. Fe2O3, CuO, ZnS, Nb2O5, CdO, CdS, Sb2O3, CeO2, HgO, Pb2O3, PbO2 and Bi2O3 are selective in photodegrading the fifteen phenols; however, the phenols get adsorbed over all sixteen particulate semiconductors.

Kinetics of phenol and m-cresol biodegradation by an indigenous mixed microbial culture isolated from a sewage treatment plant

An acclimatized mixed microbial culture, predominantly Pseudomonas sp., was enriched from a sewage treatment plant, and its potential to simultaneously degrade mixtures of phenol and m-cresol was investigated during its growth in batch shake flasks. A 2(2) full factorial design with the two substrates at two different levels and different initial concentration ranges (low and high), was employed to carry out the biodegradation experiments. The substrates phenol and m-cresol were completely utilized within 21 h when present at low concentrations of 100 mg/L for each, and at high concentration of 600 mg/L for each, a maximum time of 187 h was observed for their removal. The biodegradation results also showed that the presence of phenol in low concentration range (100-300 mg/L) did not inhibit m-cresol biodegradation. Whereas the presence of m-cresol inhibited phenol biodegradation by the culture. Moreover, irrespective of the concentrations used, phenol was degraded preferentially and earlier than m-cresol. A sum kinetics model was used to describe the variation in the substrate specific degradation rates, which gave a high coefficient of determination value (R2 > 0.98) at the low concentration range of the substrates. From the estimated interaction parameter values obtained from this model, the inhibitory effect of phenol on m-cresol degradation by the culture was found to be more pronounced compared to that of m-cresol on phenol. This study showed a good potential of the indigenous mixed culture in degrading mixed substrate of phenolics.

Feasibility of m-cresol degradation using an indigenous mixed microbial culture with glucose as co-substrate

An indigenous mixed culture of microorganisms, isolated from the soil of a gasoline filling station, was used in degrading m-cresol in presence of glucose as an alternative carbon source. Initial glucose concentration was kept at either 250 or 500 mg l−1, to initiate and support necessary culture growth, and that of m-cresol was varied between 50 and 400 mg l−1. A maximum total biomass yield value of 0.925 g g−1 was obtained at 100 mg l−1m-cresol and 500 mg l−1 glucose initial concentrations in the media. Variation in the experimentally observed specific growth rate revealed that m-cresol initial concentrations, above 100 mg l−1, inhibited the culture growth irrespective of the glucose concentrations used in the study. Complete degradation of m-cresol was observed within a time period of 18–26 h depending upon the initial concentrations of m-cresol and glucose in the media; on the other hand, glucose utilization was quick and preceded m-cresol degradation. A sum kinetics model was used to describe the variation in the culture specific growth rate, which gave a high coefficient of determination (R2) value >0.98. From the interaction parameter values obtained by solving this model, the inhibitory effect of glucose on m-cresol degradation by the culture was found to be more pronounced compared to the effect of m-cresol on glucose utilization. This study showed good potential of the indigenous mixed culture in degrading m-cresol when it is provided with a simple alternative carbon source, such as glucose, for supporting its growth.

Comparative study of phenolic compounds mixtures

The photocatalytic degradation of catechol, resorcinol, m-cresol, o-cresol and phenol has been studied individually, in dual mixtures and in the presence of hydrogen peroxide to determine possible competition for adsorption and photoactive centres and for the radicals photogenerated. The obtained results have shown that in the presence of hydrogen peroxide degradation rates are determined by the localization of specific adsorption centres more than by the amount of adsorbed molecules or the number of aromatic ring activating positions generated by substituents. The interaction of catechol with the hydroxyls responsible for the formation of the more photoactive OH radicals slows down the degradation of the other phenolics. Additionally, the interaction of each compound with the surface of TiO 2 results in the change of the photoadsorption of oxygen. Consequently, degradation rates of the mixtures are also determined by the photoadsorption of oxygen.

Degradation of some phenol derivatives by Trichosporon cutaneum R57

The purpose of the present study was to determine whether Trichosporon cutaneum R57 was able to grow and utilize some phenol derivatives: resorcinol, 2,6-dinitrophenol, 3-nitrophenol, 4-nitrophenol and m-cresol as sole carbon and energy source. The results obtained showed the ability of the strain to develop by degrading these compounds, except 4-nitrophenol. Resorcinol and 2,6-dinitrophenol were utilized in 27 h in yeast nitrogen base (YNB) medium while 3-nitrophenol and m-cresol were only partly degraded in this period of time. The growth of T. cutaneum using YNB containing one of the phenol derivatives as the sole carbon and energy source was compared with the growth of cells in YNB with the same concentration of the phenol derivative plus 0.3 g l −1 phenol. Both compounds were simultaneously utilized by the mechanism of cometabolic degradation. HPLC analysis of the centrifuged culture medium showed an increased degradation rate of resorcinol. Resorcinol and phenol were completely degraded in 18 h. No significant change of the degradation rate for 2,6-dinitrophenol and 3-nitrophenol was observed. The combination of m-cresol and phenol exhibited inhibiting effects with negligible degradation of phenol and m-cresol in 27 h. The biodegradation of the phenolic derivatives by cells of T. cutaneum R57 immobilized onto polyamide and polyacrylonitrile granules and fibers was also studied. The results were similar to these obtained from free cells, although the period of biodegradation was found to be by ca. 3 h longer.

The Role of the Liquid Phase in the Degradation of Toluene and m-Cresol within a Biofilm Trickle-Bed Reactor

The degradation of toluene and m-cresol in a biofilm trickle-bed reactor was experimentally and theoretically investigated. Degradation is the result of the cooperation between suspended and immobilized microorganisms in the trickling film and the biofilm. The role of the trickling film is that of a barrier for mass transfer to the biofilm or that of an additional reaction space. This is the result of physical availability of pollutants to the liquid phase as well as co-substrate degradation of inherent biomass. An instationary reactor balance model is presented. In addition to this the change in wetting behavior of carrier surface due to biofilm formation is discussed. A partial wetting of biofilm surface by rivulets of the trickling film is proposed. The model was verified by experimental data. The different reactor operation modes denoted as biofilm regime versus trickling film regime for the chosen pollutant system were expressed in terms of dimensionless reactions and transfer numbers. It is shown that the volumetric reaction rates for toluene in a trickling film regime reaches values twice as high as that of a biofilm regime due to the presence of the second substrate m-cresol. The limiting step in both cases is the mass transfer of oxygen to bacteria in the biofilm or trickling film.

Anaerobic degradation of m-cresol by Desulfobacterium cetonicum is initiated by formation of 3-hydroxybenzylsuccinate.

The anaerobic bacterium Desulfobacterium cetonicum oxidized m-cresol completely with sulfate as electron acceptor. During growth, 3-hydroxybenzylsuccinate (identified by gas chromatography/mass spectroscopy and by comparison of high-performance liquid chromatography retention time and UV spectrum with a chemically synthesized reference compound) accumulated in the medium. This finding indicates that the methyl group of m-cresol is activated by addition to fumarate as in the case of anaerobic toluene metabolism. In cell-free extracts of D. cetonicum, the formation of 3-hydroxybenzylsuccinate from m-cresol and fumarate was detected at an activity of 0.5 nmol min(-1) (mg protein)(-1). This reaction depended strictly on anoxic assay conditions. Treatment with air resulted in a complete loss of activity; however, some activity could be recovered after restoring anoxic conditions. The activity was slightly membrane-associated. 3-Hydroxybenzylsuccinate was degraded via CoA thioesterification and further oxidation to 3-hydroxybenzoyl-CoA as subsequent steps in the degradation pathway.

Interactions of Methanogens and Denitrifiers in Degradation of Phenols

Experiments were conducted at 37°C in an upflow anaerobic sludge blanket reactor treating wastewater containing phenol (200 mg/L), m-cresol (100 mg/L), and nitrate at various concentrations. Results show that anaerobic sludge was able to conduct denitrification without much acclimation. Denitrifiers outcompeted methanogens for substrates for carbon and electron supplies. They were able to use phenol and m-cresol as substrate without a carbohydrate cosubstrate. Denitrifying 1 g of NO3--N required 3.34 g of chemical oxygen demand. Methanogenesis occurred only at chemical oxygen demand/NO3--N ratios greater than 3.34. At the ratio of 5.23, over 98% of phenol but only 60% of m-cresol were degraded jointly by denitrifiers and methanogens with 1 day of hydraulic retention. At ratios less than 3.34, methanogenesis ceased to take place and denitrification became incomplete because of insufficient supply of substrate. Batch tests further confirmed that degradation of m-cresol was enhanced not only by the presence of nitrate, but also by the presence of either sucrose or phenol as cosubstrate.

Anaerobic Degradation of m-Cresol by a Sulfate-Reducing Bacterium

m-Cresol metabolism under sulfate-reducing conditions was studied with a pure culture of Desulfotomaculum sp. strain Groll. Previous studies with a sulfate-reducing consortium indicated that m-cresol was degraded via an initial para-carboxylation reaction. However, 4-hydroxy-2-methylbenzoic acid was not degraded by strain Groll, and no evidence for ring carboxylation of m-cresol was found. Strain Groll readily metabolized the putative metabolites of a methyl group oxidation pathway, including 3-hydroxybenzyl alcohol, 3-hydroxybenzaldehyde, 3-hydroxybenzoic acid, and benzoic acid. Degradation of these compounds preceded and inhibited m-cresol decay. 3-Hydroxybenzoic acid was detected in cultures that received either m-cresol or 3-hydroxybenzyl alcohol, and trace amounts of benzoic acid were detected in m-cresol-degrading cultures. Therefore, we propose that strain Groll metabolizes m-cresol by a methyl group oxidation pathway which is an alternate route for the catabolism of this compound under sulfate-reducing conditions.

Anaerobic degradation ofm-cresol via methyl oxidation to 3-hydroxybenzoate by a denitrifying bacterium

The anaerobic degradation ofm-cresol was studied in a denitrifying bacterium. In the initial studies, hypothetical intermediates ofm-cresol degradation were tested in growth experiments and in adaptation studies with dense cell suspensions. Results suggested a degradation ofm-cresol via 3-hydroxybenzoate. To verify this, the degradation ofm-cresol was followed in concentrated cell suspensions in the presence of metabolic inhibitors. Fluoroacetate treatment resulted in the transient accumulation of substantial amounts of 3-hydroxybenzoate. In the presence of iodoacetamide, not only was 3-hydroxybenzoate transiently formed, but benzoate was also accumulated. These findings support a degradation ofm-cresol via initial anaerobic methyl oxidation to 3-hydroxybenzoate, followed by reductive dehydroxylation to benzoate or benzoyl-CoA. Studies with extracts ofm-cresol-grown cells showed the presence of several enzyme activities to be postulated for this pathway. No evidence was found for a carboxylation, hydroxylation of the aromatic ring, or direct ring reduction as the initial step inm-cresol metabolism.

Use of Fluorinated Compounds To Detect Aromatic Metabolites from m -Cresol in a Methanogenic Consortium: Evidence for a Demethylation Reaction

Anaerobic sewage sludge was used to enrich a methanogenic m-cresol-degrading consortium. 6-Fluoro-3-methylphenol was synthesized and added to subcultures of the consortium with m-cresol. This caused the accumulation of 4-hydroxy-2-methylbenzoic acid. In a separate experiment, the addition of 3-fluorobenzoic acid caused the transient accumulation of 4-hydroxybenzoic acid. Inhibition with bromoethanesulfonic acid caused the accumulation of benzoic acid. Thus, the proposed degradation pathway was m-cresol --> 4-hydroxy-2-methylbenzoic acid --> 4-hydroxybenzoic acid --> benzoic acid. The m-cresol-degrading consortium was able to convert exogenous 4-hydroxybenzoic acid and benzoic acid to methane. In addition, for each metabolite of m-cresol identified, the corresponding fluorinated metabolite was detected, giving the following sequence: 6-fluoro-3-methylphenol --> 5-fluoro-4-hydroxy-2-methylbenzoic acid --> 3-fluoro-4-hydroxybenzoic acid --> 3-fluorobenzoic acid. The second step in each of these pathways is a novel demethylation which was rate limiting. This demethylation reaction would likely facilitate the transformation of the methyl group to methane, which is consistent with the results of a previous study that showed that the methyl carbon of m-[methyl-C]cresol was recovered predominantly as [C]methane (D. J. Roberts, P. M. Fedorak, and S. E. Hrudey, Can. J. Microbiol. 33:335-338, 1987). The final aromatic compound in the proposed route for m-cresol metabolism was benzoic acid, and its detection in these cultures merges the pathway for the methanogenic degradation of m-cresol with those for the anaerobic metabolism of many phenols.

Carboxylation and mineralization ofm-cresol by a sulfate-reducing bacterial enrichment

An enrichment culture that anaerobically degradedm-cresol under sulfate-reducing conditions was obtained from an anoxic aquifer.m-Cresol removal by the culture was greatest when sulfate or thiosulfate served as electron acceptors; sulfite, nitrate, and CO2 were poor substitutes for sulfate. A14C-labeled carboxylated intermediate was detected when the culture was given14C-labeled bicarbonate and nonlabeledm-cresol or nonlabeled bicarbonate and14C-labeledm-cresol. Metabolism of the carboxylated intermediate yielded14C-acetate, which was eventually converted to14CO2. Trace quantities of methylbenzoic acid were also detected as a putativem-cresol intermediate. The importance of this dehydroxylated intermediate in the anaerobic degradation ofm-cresol is unclear, since an amendment of 2-methylbenzoic acid was not degraded by the culture. The stoichiometry of electron acceptor consumption and carbon mass balances confirm thatm-cresol was mineralized by the culture.

The methanogenic degradation of m-cresol and related aromatic compounds

The methanogenic degradation of m-cresol and related aromatic compounds

Anaerobic degradation of m-cresol in anoxic aquifer slurries: carboxylation reactions in a sulfate-reducing bacterial enrichment

The anaerobic biodegradation of m-cresol was observed in anoxic aquifer slurries kept under both sulfate-reducing and nitrate-reducing but not methanogenic conditions. More than 85% of the parent substrate (300 microM) was consumed in less than 6 days in slurries kept under the former two conditions. No appreciable loss of the compound from the corresponding autoclaved controls was measurable. A bacterial consortium was enriched from the slurries for its ability to metabolize m-cresol under sulfate-reducing conditions. Metabolism in this enrichment culture was inhibited in the presence of oxygen or molybdate (500 microM) and in the absence of sulfate but was unaffected by bromoethanesulfonic acid. The consortium consumed 3.63 mol of sulfate per mol of m-cresol degraded. This stoichiometry is about 87% of that theoretically expected and suggests that m-cresol was largely mineralized. Resting-cell experiments demonstrated that the degradation of m-cresol proceeded only in the presence of bicarbonate. 4-Hydroxy-2-methylbenzoic acid and acetate were detected as transient intermediates. Thus, the parent substrate was initially carboxylated as the primary degradative event. The sulfate-reducing consortium could also decarboxylate p- but not m-hydroxybenzoate to near stoichiometric amounts of phenol, but this reaction was not sulfate dependent. The presence of p-hydroxybenzoate in the medium temporarily inhibited m-cresol metabolism such that the former compound was metabolized prior to the latter and phenol was degraded in a sequential manner. These findings help clarify the fate of a common groundwater contaminant under sulfate-reducing conditions.

Photocatalyzed mineralization of cresols in aqueous media with irradiated titania

Titania, Ti0 2, irradiated by ultraviolet/visible light was used to mediate the photocatalyzed degradation of ortho-cresol, meta-cresol, and para-cresol. The total photomineralization of these phenols to carbon dioxide and water occurs in air-equilibrated aqueous media. Two major hydroxylated aromatic intermediate species have been identified by liquid chromatographic methods: 4-methylcatechol and methylhydroquinone. Photochemical efficiencies (lower limits of quantum yields, 365 nm) of compound disappearance are, respectively, 0.0096, 0.0076, and 0.010 for o-, m-, and p-cresol. The effect of such parameters as pH, initial cresol concentration, and radiant power levels on the degradation of m-cresol was examined in detail. Although the photodegradation process kinetics show similarities with Langmuir-Hinshelwood-type behavior, namely saturation, it is shown that the resulting kinetic expression for the rate of degradation is a complicated function of various parameters and is silent as to the details of the initial photooxidative steps. It is implicitly argued, however, that the reaction takes place on the semiconductor particle surface.

Culture methods for obtaining m-cresol-degrading methanogenic consortia

Studies of the metabolism of m-cresol under methanogenic conditions have been hampered by difficulties in enriching and maintaining active consortia. With anaerobic sewage sludge as an inoculum, m-cresol degradation was shown to be inhibited by sodium sulfide at concentrations typically used to pre-reduce culture medium. In enrichment cultures, the acclimation time for m-cresol degradation was shortened from 61 days to 37 days by using diluted (24% vol/vol) sludge rather than concentrated (96%) sludge, which contained 0.8 mM total sulfide. The m-cresol degrading activity of enrichment cultures transferred to fresh medium was greater when iron nails or amorphous ferrous sulfide were used as a reducing agent in place of sodium sulfide.

The effects of cyanide on the methanogenic degradation of phenolic compounds

The effects of cyanide on the degradation of phenol, m-cresol, p-cresol, catechol and hydroquinone in acclimated methanogenic consortia were studied. Batch cultures with cyanide concentrations up to 10 mg l −1 were monitored for phenolic removal and methane production. Results showed that the methanogens were more sensitive to cyanide inhibition than the phenolic-degrading bacteria. The former group was inhibited by lower cyanide concentrations and took longer to adapt to the toxicant. Phenolic degradation was slowed to varying degrees depending upon the phenolic substrate. The addition of 400 mg l −1 acetate or 10 −2 M bromoethanesulfonic acid, a specific inhibitor of methanogenesis, also slowed the rates of phenolic degradation. Thus cyanide can affect a phenolic-degrading consortium by causing an accumulation of endproducts of the non-methanogenic fermentation (e.g. acetate) because of the inability of the methanogens to consume them. A draw and feed culture adapted to phenol degradation in the presence of 5 mg l −1 cyanide was able to produce methane from feed solutions containing 5 mg l −1 cyanide and 250 mg l −1 phenol at the same rate as a control culture receiving 250 mg l −1 phenol but no cyanide.

Pathways for the degradation of m-cresol and p-cresol by Pseudomonas putida.

A comparison of the oxidation rates of various compounds by whole cells of Pseudomonas putida 3, 5 indicated that m-cresol is metabolized by oxidation to 3-hydroxybenzoate followed by hydroxylation to gentisate, the ring-fission substrate, when grown with 3, 5-xylenol. However, when m-cresol was the growth substrate, similar experiments suggested a different pathway involving a methyl-substituted catechol, and ring-fission by meta cleavage. Assays of ring-fission enzymes in cell-free extracts confirmed that different pathways are induced by the two growth substrates. 3, 5-Xylenol-grown cells contained high levels of gentisate oxygenase and only very small amounts of catechol oxygenase, whereas gentisate ocygenase could not be detected in m-cresol-grown cells, but levels of catechol oxygenase were greatly increased. Extracts of m-cresol-grown cells also contained 2-hydroxymuconic semialdehyde dehydrogenase and hydrolase, whose specificities enable them to metabolize the ring-fission products from catechol, 3-methylcatechol, and 4-methylcatechol. This catechol pathway is also used by m-cresol-grown cells for p-cresol metabolism. In contrast, the results for cells grown with p-cresol point to an alternative pathway involving oxidation to 4-hydroxybenzoate and hydrosylation to protocatechuate as ring-fission substrate. Extracts of these cells contained high levels of protocatechuate oxygenase and only small amounts of catechol oxygenase.