Aqueous Phenols Research Articles

Upgrading of cow manure by hydrothermal carbonization: Evaluation of fuel properties, combustion behaviors and kinetics

The rational thermochemical conversion of livestock manure holds significant implications for the recovery and utilization of wastes. In this study, cow manure (CM) was treated by hydrothermal carbonization (HTC) to evaluate the fuel properties, combustion behavior and kinetics of hydrochars. The results showed that HTC increased the carbon content of CM from 37.02% to 43.68% and the H/C and O/C ratios comparable to lignite. The oxygen-containing functional groups of hydrochars decreased and displayed typical deposition micromorphology of secondary char. For aqueous phase, furans and phenols were enriched at 200 °C and 260 °C respectively, which were the main precursor or/and components of secondary char. The thermogravimetric analysis displayed hydrochars combustion were more stable and lasting. The secondary char reduced ignition temperature, but limited impact on volatilization during combustion. Compared with CM, hydrochars showed lower activation energy in initial combustion, and higher at high conversions (except for CM260). The relative lower activation energy of CM260 was mainly attribute to the loose ash structure. Besides, HTC could alleviate slagging/fouling of CM combustion and high temperature strengthened the effect. These results indicate that HTC is a promising approach to treat CM for solid fuels, and 240 °C is suggested to upgrading the characteristics.

Eu3+ doped Bi2MoO6 nanosheets fabricated via hydrothermal-calcination route and their superior performance for aqueous volatile phenols removal

(1) Background The discharge of volatile phenols, e.g., phenol, 2-methyl phenol, 3-methyl phenol, and 4-methyl phenol, into the aquatic system represents a main source of environmental contamination due to their high toxicity. Detoxication of phenol molecules from polluted water through photocatalytic degradation process is reported to be a mild and effective technology. (2) Methods In this study, to effectively remove these aqueous volatile phenols, a powerful photocatalyst, namely Eu3+doped Bi2MoO6 nanosheets, was prepared via a hydrothermal-calcination process. The novel Eu3+doped Bi2MoO6 nanosheets were characterized by XRD, BET, SEM, TEM, XPS, UV–vis DRS, FT-IR, PL and photoelectricity test. Under xenon lamp light illumination, Eu/Bi2MoO6 was used to degrade the volatile phenols. (3) Significant findings The results showed that the doping of Eu3+ into Bi2MoO6 crystals induced a distortion of Bi2MoO6 lattice and a decrease in crystalline grain size. Eu3+ doping also reduced the energy gap of Bi2MoO6 and increased its UV–Vis light absorption. Moreover, the doped Eu3+could act as electron traps to decrease the recombination rate of the e−/h+ pairs. The doping of Eu3+ with optimum content (ཞ2% molar ratio of Eu3+ to Bi3+) gave a rise two times increase in activity for phenols decomposition.

Control of bacterial and fungal biofilms by natural products of Ziziphus joazeiro Mart. (Rhamnaceae)

The aim of this study is to verify the action of the aqueous leaf extract Ziziphus joazeiro in the eradication of bacterial and fungal biofilms, and to compare these effects with the stem bark extracts, as well as with conventional standard drugs. The presence of secondary metabolites was observed through phytochemical prospection assays. The effect of the aqueous extract on microbial biofilm formation was observed by OD600 nm absorbance and the crystal violet assay. For bacterial and fungal biofilms, chlorhexidine gluconate and fluconazole, respectively, were used as positive controls. Phytochemical characterization showed the presence of secondary metabolite classes common to both extracts such as flavonoids, steroids and saponins. In particular, in the aqueous leaf extract phenols, condensed tannins and alkaloids were observed. Eradication results using the aqueous leaf extract showed an inhibition of the microbial biofilm mass, moreover the biofilms were more sensitive to the bark extract, which presented a greater inhibition number and an action similar to standard drugs. It is important to highlight the leaf extract showed significant eradication at the lowest concentrations for mature yeast biofilms, thus demonstrating its potential to modify microbial resistance susceptibility. Bacterial and fungal biofilm eradication results using the Ziziphus joazeiro aqueous extracts presented a biofilm inhibition effect for both, moreover the results support the ethnopharmacological knowledge surrounding the use of Ziziphus joazeiro stems in the community. In comparison, the bark extract presented a more effective treatment than the leaf extract against biofilms, presenting inhibition levels similar to the used standard drugs.

Packed Bed Column for Adsorption of Aqueous Phenols on Cement Kiln Dust

AbstractCement kiln dust (CKD) must be disposed of properly, otherwise it may cause severe pollution. The optimum solution is to minimize the undesirable environmental impacts as well as economical...

Modelling the transient kinetics of laccase-catalyzed oxidation of four aqueous phenolic substrates at low concentrations

Laccase catalyzes the oxidation of aqueous phenolic substrates by oxygen. To assess the feasibility of using this enzyme to oxidize aqueous phenols at low concentrations, a five-parameter kinetic model was developed based on previous work to predict the transient kinetics of reactions catalyzed by laccase from Trametes versicolor. The model was calibrated against data collected at pH 5.0 and 25 °C for batch reactions of triclosan, cumylphenol, and estradiol. Phenol data arising from an earlier study was used for comparison. The kinetic model, which incorporated a term for enzyme inactivation, accurately simulated the time course of reactions of all four compounds for ranges of substrate and laccase concentrations that spanned up to 5 orders of magnitude. Furthermore, it was demonstrated that the model made accurate predictions far outside of the range of its calibration. The utility of the model for assessing the feasibility of using laccase to catalyze the oxidation of substrates over a range of reactant concentrations was demonstrated. Modelling and experimental results showed that estradiol, cumylphenol and triclosan can be oxidized through the catalytic action of laccase at aqueous substrate concentrations in the micromolar to nanomolar concentration range, while using substantially less enzyme than required for phenol.

ARTICHOKE PEROXIDASE TO PARTIAL REMOVAL OF PHENOLS FROM OLIVE MILL WASTE WATER

A very large amount of phenol-polluted waters is formed from the production of olive oil (olive mill waste water, OMWW) and their disposal represents a serious problem. The aim of this study was to investigate the use of peroxidase (POD) from artichoke (Cynara cardunculus L. subsp. scolymus (L.) Hayek) leaves to remove phenols present in OMWW. The POD catalyzes the polymerization and precipitation of aqueous phenols. This application could be useful, because in the Mediterranean region a large amount of OMWW as well as a lot of artichoke scraps resulting from artichoke processing industry, are produced. So, it is possible to consider this biomass (leaves and external bud bracts) as a useful and cheap source of peroxidase. The enzyme extraction was performed by homogenization and separation of pigments using an aqueous two phase polymer system (polyethylene glycol/(NH4)2SO4), that allowed the accumulation of POD in the salt phase. The optimal reaction conditions were evaluated. The phenolic concentration was assayed by Folin-Ciocalteu method. Preliminary results showed that the optimal conditions for enzyme activity were in a broad range of both pH (from 4 to 7) and temperature (from 5 to 50°C). In optimal enzymatic conditions, a reduction of more than 60% of initial phenolic concentration was observed.

QCM sensors for aqueous phenols based on active layers constituted by tetrapyrrolic macrocycle Langmuir films

Three different metalated tetrapyrrolic macrocycles have been transferred by Langmuir-Blodgett technique directly onto piezoelectric quartz crystal covered with gold electrodes of a commercial quartz crystal microbalance instrument in order to perform a flow injection analysis. All floating films at the air-water interface have been analyzed by registration of Langmuir curves and by UV-vis reflection spectroscopy and brewster angle microscopy. The sensing performances of the modified gold electrodes were investigated by monitoring the frequency variation induced by the presence of several toxic phenols. The explored concentrations ranged around 10-3 M and the corresponding frequency variations ranged between 10 and 200 Hz. All responses observed were fast, reproducible and reversible; moreover, the active layers are stable over long periods of utilization. The observation that interferences from fulvic acid are absolutely negligible is also noteworthy. The responses are not selective for each singular phenol derivative; notwithstanding this, to the best of our knowledge, this contribution represents one of the first examples of sensing layers for the monitoring of the total content of phenols.

Comparison of soybean peroxidase with laccase in the removal of phenol from synthetic and refinery wastewater samples

AbstractBACKGROUND: Several studies have demonstrated the feasibility of treating aqueous phenols and aromatic amines with oxidoreductases in synthetic wastewater samples. However, little work has been done on the effectiveness of enzymatic treatment on real wastewater. Here a comparison was made of the oxidative coupling of phenol catalyzed by laccase or soybean peroxidase (SBP) using synthetic and refinery wastewaters.RESULTS: Optimization of pH, enzyme concentration, effect of polyethylene glycol (PEG) addition, and reducing anions were examined for a 3 h reaction time. Laccase had an optimum pH of 5.6–6.0, while SBP had a broad optimum from 6.0 to 8.0. In synthetic samples in tap water to achieve ≥ 95% removal of 1.0 mmol L−1 phenol in 3 h required 0.12 and 1.5 U mL−1 of catalytic activity of laccase and SBP, respectively. In refinery samples comparable removals required 1.2‐ to 1.8‐fold more enzyme than in synthetic tap water samples. Added PEG allowed for a small reduction in the SBP concentration for synthetic wastewater but was ineffective with either enzyme in treating refinery samples. Reducing ions increased the demand for oxidant but, with the exception of cyanide, phenol removal still occurred.CONCLUSION: Both laccase and SBP were effective in removing phenol from aqueous refinery samples, albeit at slightly higher concentrations than required for the corresponding synthetic samples. Copyright © 2008 Society of Chemical Industry

Reconstruction of Dynamics of Aqueous Phenols and Their Products Formation in Ozonation Using Differential Neural Network Observers

A differential neural network (DNN) is used to estimate the state dynamics in the phenols−ozone−water system of the model solution of phenol (PH), 4-chlorophenol (4-CPH), and 2,4-dichlorophenol (2,4-DCPH). This new technique, which is based on a differential neural network observer (DNNO), is applied to estimate decomposition dynamics of phenols, byproducts accumulation and decomposition, and final products accumulation. It is considered to be a process with an uncertain model (“black-box”) and is affected by internal (variation of experimental conditions) and external perturbations (measurement noises). The monitored ozone concentration in the gas phase in the reactor outlet is used to obtain the summary characteristic curve (ozonogram) in ozonation. The proposed DNNO is trained using the variation of this parameter with the experimental data of the phenols decomposition, obtained using the HPLC technique, at pH 2 and pH 9. The trained DNNO then is applied to reconstruct the dynamics of the phenols decom...

Effect of pH to the decomposition of aqueous phenols mixture by ozone

The degradation of the mixture of phenol and its chlorinat- ed derivatives with ozone is studied. The studied compounds are phe- nol (Ph), 4 - chlorophenol (4-CPh) and 2,4 - dichlorophenol (2,4- DCPh). The kinetic performances of each phenolic compound in the model mixture are examined. The pH influence to the decomposition dynamics for different phenolic compounds in the range 2 - 12 is investigated. The increase of the decomposition rate under the pH increasing was observed. In the studied pH range, phenol and chlorophenols ozonation proceeds rapidly. The UV absorvency is used for the preliminary control of the phenols decomposition degree. The HPLC analysis was used to identify intermediates and final prod- ucts formed during ozonation of the phenols mixture. It is shown that the basic intermediates are muconic and fumaric acids, malonic and maleic acids, catechol and hydroquinone. The final products are oxal- ic acid and formic acid. In the case of alkaline media, the principal final product is oxalic acid. Furthermore, intermediates and final decomposition products obtained at the different pH are compared. According to the obtained results, the possible mechanism of ozona- tion by the reaction of hydroxylation and dechloration in the early stage is proposed. The BOD 5 /COD ratio is used as a biodegradability measure for the comparison of biodegradability of initial compounds and final products composition.

Electrochemical degradation of aqueous phenols using graphite electrode in a divided electrolytic cell

Untreated industrial effluents invariably contain large amounts of heavy metals and organics. This paper reports the electrochemical oxidation of synthetic water containing 200 ppm of phenol. Studies have been carried out in a compartmentalized cell using platinum (cathode) and graphite (anode). Electrolysis has been done for 40 h at constant applied potential of 5 V in different electrolytes, such as, NaCl (aq), NaOH (aq) and a mixture containing both NaCl (aq) and NaOH (aq) as the anolyte and acid as the catholyte. Phenol concentration decreased from the initial value of 200 to about 10 ppm.; the corresponding COD values, respectively, are ∼400 to ∼100 ppm. The reaction goes through chloro-compounds as intermediates before being mineralized. The carbon anode seems to be passivated with a thin layer of poly-phenol. A concomitant amount of hydrogen is generated during the electrolytic degradation of phenol.

Hydroxyl free radical reactivity toward aqueous chlorinated phenols

Second-order kinetic constants (k(OH,S)) for the hydroxyl free radical attack on a series of nine chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, 2,3,5,6-tetrachlorophenol, 2,3,4,5-tetrachlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorophenol) in aqueous solution were determined by means of the competitive kinetics method. Experimental values ranged from 3.5 x 10(09)M(-1)s(-1) for pentachlorophenol to 8.2 x 10(09)M(-1)s(-1) for 2-chlorophenol. A general trend of lower kinetic constant values with higher degree of chlorination was observed and tested with four different correlations using Hammett's sigma values, the number of chlorine substituents on the aromatic ring, and estimated diffusion coefficients. These correlations were statistically significant (alpha=0.01), although the regression coefficients were moderate (R(2)<0.6). Statistical analysis indicated that all correlations were equally valid. This report includes second-order kinetic constants not previously reported for six chlorophenols, and also provides the means to estimate constants for other chlorophenols for which no experimental data are available.

Hydrophilic and lipophilic antioxidant activity changes during on-vine ripening of tomatoes (Lycopersicon esculentum Mill.)

Changes in antioxidant activity during the on-vine ripening of tomatoes (Lycopersicon esculentum) were studied at four different ripening stages (green, breaker, pink and red ripe). Hydrophilic and lipophilic antioxidant activities (HAA and LAA, respectively) were determined and their relationships to ascorbic acid, total phenols, lycopene and β-carotene contents were analysed. HAA and ascorbic acid remained practically unchanged, while the levels of aqueous phenols increased during ripening. The levels of ascorbic acid and HAA were strongly correlated (r=0.90, P<0.1). β-Carotene increased until breaker and pink stages, decreasing afterwards. In contrast, lycopene accumulated throughout the ripening period. The LAA followed the same pattern as lycopene and a good correlation was found (r=0.91, P<0.05). There was less difference between the measured and calculated LAA as the lycopene level increased, the discrepancy being lowest at the red-ripe stage, indicating the importance of lycopene as a lipophilic antioxidant in tomatoes.

Characterization of tyrosinase for the treatment of aqueous phenols

Mushroom tyrosinase (polyphenol oxidase, EC 1.14.18.1) was investigated as an alternative to peroxidase enzymes for the catalytic removal of phenolic compounds from wastewaters. Maximum catalytic activity was observed at pH 7 and more than 50% of optimum activity was observed at pHs ranging between 5 and 8. Tyrosinase was unstable under acidic conditions and at elevated temperatures. The activation energy for thermal inactivation of tyrosinase at pH 7 was determined to be 1.85 kJ mol −1 using l-tyrosine as a substrate. Phenol was successfully transformed by tyrosinase over wide ranges of pH 5–8 and initial phenol concentration (0.5–10 mM, 47–940 mg/l). Several chlorinated phenols were also successfully transformed. Polyethylene glycol and chitosan did not protect tyrosinase from inactivation during the treatment of phenol; however, chitosan induced the precipitation of reaction products arising from phenol transformation.

Characterization of soybean peroxidase for the treatment of aqueous phenols

The application of soybean peroxidase (SBP) to catalyze the polymerization and precipitation of aqueous phenols by hydrogen peroxide is potentially promising because this peroxidase is less expensive than horseradish peroxidase (HRP), which has been the focus of most wastewater research. SBP can act on a broad range of compounds and retains its catalytic ability over wide ranges of temperature and pH. Activity was optimal at pH 6.4, with significant activity observed between pH 3 and 9. SBP was very stable at 25°C at neutral and alkaline conditions but experienced rapid inactivation below pH 3. SBP underwent biphasic inactivation by hydrogen peroxide in the absence of a reductant substrate. SBP was most effective when used to treat phenolic solutions between pH 6 and 9. In comparison with HRP, the activity of SBP was only slightly more sensitive to pH, was more stable at elevated temperatures, and was less susceptible to permanent inactivation by hydrogen peroxide. However, SBP was catalytically slower than HRP and a larger molar quantity of SBP was usually required to remove a given quantity of phenolic substrate.

Direct acetylation followed by solid-phase disk extraction and GC-ITDMS for the determination of trace phenols in water

A rapid, accurate and sensitive method is described for the analysis of phenolic compounds, including phenol, alkylphenols, halogenated phenols and nitrophenols in tap, ground and river water samples. The method consists in direct acetylation of the aqueous phenols with acetic anhydride, extraction of the phenol acetates with a C18 disk and analysis by gas chromatography with an ion-trap detector mass spectrometer. Using this method, the sample preparation time was approximately 1.5 h for six 1-L water samples, and recoveries for most of the phenolic compounds studied were more than 80% at concentration levels of 0.1 and 1.0μg L−1. The detection limits were in the range 2 to 15 ng L−1 for phenol, alkylphenols and halogenated phenols, and 25 to 50 ng L−1 for nitrophenols.

Diffusion coefficients of aqueous phenols determined by the Taylor dispersion technique. Evidence for solute adsorption on the walls of Teflon tubing

The Taylor dispersion technique has been used to determine the diffusion coefficients of the m-alkoxyphenol and alkyl p-hydroxybenzoate homologous series in aqueous 5 × 10–3 mol dm–3 NaOH solutions and water–ethanol mixtures. The deviations from the expected behaviour for the higher homologues increase with the eluent water content and are attributed to solute adsorption on the walls of the Teflon dispersion tube. However, the adsorption corrections performed using Golay's equation for capillary chromatography do not account for all the diffusion coefficient deviations. The experimental solute hydrodynamic radii, calculated through the Stokes–Einstein equation, decrease as the eluent ethanol content is increased. These radii are smaller than those estimated by using atomic contributions or by adding the atomic van der Waals radii to the solute optimized geometry.

High-precision sampling of trace gas-borne volatiles by the dynamic solvent effect with a comparative review of alternative techniques

The precise determination of traces of organic volatiles is particularly challenging in semiochemistry and clinical chemistry, where specimen sizes are intrinsically limited and amounts of trace components correspondingly very small. This demands a sampling technique that is fully compatible with the ability of capillary columns and gas chromatographic detectors to separate and quantify nanogram and sub-nanogram amounts from complex mixtures. The quantitative precision of dynamic solvent-effect sampling of low parts per billion (10 9) aqueous carbonyl compounds, high ppb and low parts per million aqueous phenols, low ppb and high parts per trillion (10 12) airborne hydrocarbons and the volatiles from wine, human urine and a slow-release pesticide was tested with specimen sizes that yielded amounts of volatiles down to the sub-nanogram level. Provided that sources of variability, such as temperature changes, adsorption on containers, incomplete peak resolution and changes in the specimens themselves, were adequately controlled, dynamic solvent-effect sampling consistently provided coefficients of variation in peak areas, peak percentage areas and peak-area ratios of less than 10% at nanogram and sub-nanogram levels. The literature was surveyed for data on the performance of other sampling systems. None of them have been demonstrated to match the precision of the dynamic solvent effect with such small amounts from such a wide range of materials.

Aerobic coupling of aqueous phenols catalyzed by binuclear copper: Ring substituent effect and the kinetics of the coupling of o‐methylphenol

AbstractThe substituent effect on the aerobic and catalytic coupling of aqueous phenols conforms to a Hammett correlation in which the reaction constant is −2.16; the results are very similar to that of the enzymatic coupling reaction, in which the reaction constant is −2.4. Deviations from the Hammett correlation are attributed to steric factor, product inhibition, and the blocking of coupling sites on phenoxy radicals. Available evidence indicates that catalytic and enzymatic coupling reactions are strikingly similar in many respects. The striking resemblance suggests a common reaction mechanism in which binuclear metal (copper or iron) plays a key role. The common mechanistic features of the coupling reactions are suggested, and the implications of the findings are discussed with reference to (1) the design of a novel dephenolization scheme, (2) the elucidation of the widely occurring but poorly understood enzymatic coupling reactions, and (3) the synthesis of active polymer‐bound coupling catalysts.

Aerobic coupling of aqueous phenol catalyzed by cuprous chloride: basis of a novel dephenolization scheme for phenolic wastewaters

The discovery that cuprous chloride can effect the aerobic coupling of aqueous phenol under mild reaction conditions had led to the proposal of a novel dephenolisation scheme for high-strength phenolic wastewaters. As envisaged, aqueous phenols will be converted aerobically and catalytically into insoluble coupling products which may then be easily separated from the wastewaters. The recovered solid organics may be disposed of as a fuel. The low costs of cuprous chloride and oxygen, the simplicity of the scheme, and the fuel value of the recovered organics make the scheme highly promising. A preliminary study with actual coal gasification wastewater confirms the promising nature of the proposed system.