Cresols utilization by <Emphasis Type="Italic">Trametes versicolor</Emphasis> and substrate interactions in the mixture with phenol

The ability of the white rot fungus Trametes versicolor strain 1 to degrade and utilize methylated phenols (cresols) was established for the first time in a medium not containing any other carbon components. The data obtained demonstrated the better potential of the strain to assimilate p-cresol instead of o- or m- cresol. The 0.5 g/l p-cresol provided was degraded in full after 96 h. The effect of a dual substrate mixture (0.3 g/l phenol + 0.2 g/l p-cresol) on the growth behavior and degradation capacity of the investigated strain was examined. The cell-free supernatants were analyzed by HPLC. It was established that the presence of p-cresol had not prevented complete phenol degradation but had a significant delaying effect on the phenol degradation dynamics. Phenol hydroxylase, catechol 1.2-dioxygenase and cis,cis-muconate cyclase activities were obtained in conditions of single and mixed substrates cultivation. The influence of different phenolic substrates on phenol hydroxylase activity in Trametes versicolor 1 was established. The mathematical models describing the dynamics of single substrates’ utilization as well as the mutual influence of phenol and p-cresol in the mixture were developed on the bases of Haldane kinetics. The estimated interaction coefficients (I _ph/cr = 4.72, I _cr/ph = 7.46) demonstrated the significant inhibition of p-cresol on phenol biodegradation and comparatively low level of influence of phenol presence on the p-cresol degradation. Molecular 18S RNA gene taxonomy of the investigated strain was performed.     

Kinetics of the biodegradation of phenol in wastewaters from the chemical industry by covalently immobilized <Emphasis Type="Italic">Trichosporon cutaneum</Emphasis> cells

A simple method for the preparation of the biocatalyst with whole cells is presented, and the applicability of the technique for biodegradation of phenol in wastewater from the chemical industries using the basidomycetes yeast Trichosporon cutaneum is explored. Kinetic studies of the influence of other compounds contained in wastewater as naphthalene, benzene, toluene and pyridine indicate that apart from oil fraction, which is removed, the phenol concentration is the only major factor limiting the growth of immobilized cells. Mathematical models are applied to describe the kinetic behavior of immobilized yeast cells. From the analysis of the experimental curves was shown that the obtained values for the apparent rate parameters vary depending on the substrate concentration (μ_maxapp from 0.35 to 0.09 h⁻¹ and K _sapp from 0.037 to 0.4 g dm⁻³). The inhibitory effect of the phenol on the obtained yield coefficients was investigated too. It has been shown that covalent immobilization of T. cutaneum whole cells to plastic carrier beads is possible, and that cell viability and phenol degrading activity are maintained after the chemical modification of cell walls during the binding procedure. The results obtained indicate a possible future application of immobilized T. cutaneum for destroying phenol in industrial wastewaters.     

Phenol and cresol mixture degradation by the yeast <Emphasis Type="Italic">Trichosporon cutaneum</Emphasis>

Most industrial wastes contain different organic mixtures, making important the investigation on the microbial destruction of composite substrates. The capability of microbes to remove harmful chemicals from polluted environments strongly depends on the presence of other carbon and energy substrates. The effect of mixtures of phenol- and methyl-substituted phenols (o-, m-, p-cresol) on the growth behaviour and degradation capacity of Trichosporon cutaneum strain was investigated. The cell-free supernatants were analysed by HPLC. It was established that the presence of o-, m- and p- cresol has not prevented complete phenol assimilation but had significant delaying effect on the phenol degradation dynamics. The mutual influence of phenol and p-cresol was investigated. We developed the kinetic model on the basis of Haldane kinetics, which used model parameters from single-substrate experiments to predict the outcome of the two-substrate mixture experiment. The interaction coefficients indicating the degree to which phenol affects the biodegradation of p-cresol and vice versa were estimated. Quantitative estimation of interaction parameters is essential to facilitate the application of single or mixed cultures to the bio-treatment of hazardous compounds.     

Degradative ability of 2,4,6-tribromophenol by saprophytic fungi Trametes versicolor and Agaricus augustus isolated from chilean forestry

Trametes versicolor and Agaricus augustus, with a maximum tolerable concentration (MTC) of 80 μg ml⁻¹ tribromophenol (TBP), were selected to evaluate TBP biodegradation capacity. These fungi were capable of decreased TBP concentrations and A. augustus was also capable of biotransforming TBP to tribromoanisole (TBA). Peroxidase and laccase activities were observed in the T. versicolor supernatant but not in that of A. augustus. These tolerance levels could be due to either lignolytic enzymes that degrade TBP or the ability of the fungi to biotransform TBP to tribromoanisole, respectively. The sustained ability of T. versicolor to degrade TBP (total of 40 μg ml⁻¹) in the presence of an additional carbon source suggests that it may have potential applications in the degradation of forestry industry waste.     

Biodegradation of phenol by immobilized Aspergillus awamori NRRL 3112 on modified polyacrylonitrile membrane

Covalent immobilization of Aspergillus awamori NRRL 3112 was conducted onto modified polyacrylonitrile membrane with glutaraldehyde as a coupling agent. The polymer carrier was preliminarily modified in an aqueous solution of NaOH and 1,2-diaminoethane. The content of amino groups was determined to be 0.58 mgeq g⁻¹. Two ways of immobilization were used—in the presence of 0.2 g l⁻¹ phenol and without phenol. The capability of two immobilized system to degrade phenol (concentration—0.5 g l⁻¹) as a sole carbon and energy source was investigated in batch experiments. Seven cycles of phenol biodegradation were conducted. Better results were obtained with the immobilized system prepared in the presence of phenol, regarding degradation time and phenol biodegradation rate. Scanning electron micrographs of the polyacrylonitrile membrane/immobilized Aspergillus awamori NRRL at the beginning of repeated batch cultivation and after the 7th cycle were compared. After the 7th cycle of cultivation the observations showed large groups of cells. The results from the batch experiments with immobilized system were compared to the results produced by the free strain. Phenol biodegradation experiments were carried out also in a bioreactor with spirally wound membrane with bound Aspergillus awamori NRRL 3112 in a regime of recirculation. 10 cycles of 0.5 g l⁻¹ phenol biodegradation were run consecutively to determine the degradation time and rate for each cycle. The design of the bioreactor appeared to be quite effective, providing large membrane surface to bind the strain.     

Biodegradation of phenol and 4-chlorophenol by the yeast <Emphasis Type="Italic">Candida tropicalis</Emphasis>

Biodegradation of phenol and 4-chlorophenol (4-cp) using a pure culture of Candida tropicalis was studied. The results showed that C. tropicalis could degrade 2,000 mg l⁻¹ phenol alone and 350 mg l⁻¹ 4-cp alone within 66 and 55 h, respectively. The capacity of the strain to degrade phenol was obviously higher than that to degrade 4-cp. In the dual-substrate system, 4-cp intensely inhibited phenol biodegradation. Phenol beyond 800 mg l⁻¹ could not be degraded in the presence of 350 mg l⁻¹ 4-cp. Comparatively, low-concentration phenol from 100 to 600 mg l⁻¹ supplied a sole carbon and energy source for C. tropicalis in the initial phase of biodegradation and accelerated the assimilation of 4-cp, which resulted in the fact that 4-cp biodegradation velocity was higher than that without phenol. And the capacity of C. tropicalis to degrade 4-cp was increased up to 420 mg l⁻¹ with the presence of 100–160 mg l⁻¹ phenol. In addition, the intrinsic kinetics of cell growth and substrate degradation were investigated with phenol and 4-cp as single and mixed substrates in batch cultures. The results illustrated that the models proposed adequately described the dynamic behaviors of biodegradation by C. tropicalis.     

Feasibility study of exponential feeding strategy in fed-batch cultures for phenol degradation using Cupriavidus taiwanensis

An indigenous phenol-degrading bacterial isolate Cupriavidus taiwanensis R186 was used to degrade phenol from an aqueous solution under fed-batch operation. An exponential feeding strategy combined with dissolved oxygen control was applied based on kinetic characteristics of cell growth and phenol degradation to meet sufficient metabolic needs for cellular growth and achieve the best phenol removal efficiency. Without the stress of phenol inhibition, the optimal set point of specific growth rate of exponential feeding for fed-batch phenol degradation was found to be 0.50–0.55μ_max (μ_max denotes the maximum specific growth rate from Monod model). Meanwhile, the sufficient set point of dissolved oxygen for maximal phenol degradation efficiency was approximately at 10–55% air saturation. With the optimal operation conditions, the best phenol degradation rate was 0.213 g phenol h⁻¹, while a shortest treatment time of 15 h was achieved for complete degradation of 11.35 mM (ca. 3.20 g) of phenol.     

Degradation of 3-chlorobenzoate and phenol singly and in mixture by a mixed culture of two ortho-pathway-following <Emphasis Type="Italic">Pseudomonas</Emphasis> strains

The compatibility and efficiency of two ortho-cleavage pathway-following pseudomonads viz. the 3-chlorobenzoate (3-CBA)-degrader, Pseudomonas aeruginosa 3mT (3mT) and the phenol-degrader, P. stutzeri SPC-2 (SPC-2) in a mixed culture for the degradation of these substrates singly and simultaneously in mixtures was studied. Another phenol-degrading strain, Pseudomonas sp. SoPC-5 (SoPC-5) that utilizes a meta-cleavage mode also was tried in co-culture with 3mT. The former combination was found to be a better degrader of both the substrates when present alone. But, with inoculum levels of 0.15 mg cell dry wt each of 3mT/SPC-2 or 3mT/SoPC-5 growth with 2 mM each of 3-CBA and phenol was slow with a lag of 24 h and degradation being incomplete. However, with higher inocula in the ratios 1:1, 1:2, and 2:1, i.e., 0.3 + 0.3, 0.3 + 0.6, and 0.6 + 0.3 mg cell dry wt of 3mT and SPC-2, respectively complete degradation of both the substrates occurred. Degradation of 3-CBA was complete with the release of stoichiometric amounts of chloride (Cl⁻) when concentrations of phenol/3-CBA were varied as 2:2, 2:4, and 4:2 mM, i.e., even when the concentration of the more toxic co-substrate 3-CBA was higher than phenol effective simultaneous degradation occurred at the inoculums ratio of 1:1 (0.3 mg dry cell wt. of each strain). These studies clearly indicated the better suitability of ortho-cleavage-utilizing strains as partners in a mixed culture than those follow different modes.     

Mutagenic and Genotoxic Effects of <Emphasis Type="Italic">cis</Emphasis>-(Dichloro)tetraammineruthenium(III) Chloride on Human Peripheral Blood Lymphocytes

Chemotherapeutic agents play an important role in cancer treatment mostly due their systemic action on human organism allowing access to liquid tumors and even metastases. Among these drugs, ruthenium compounds have been showing promising results to treat tumors and represent an important development of new antitumor therapy. This study presents the evaluation of cis-(dichloro)tetraammineruthenium(III) chloride, cis-[RuCl₂(NH₃)₄]Cl, genotoxic effects using human peripheral blood lymphocytes cultured in vitro. Mitotic index (MI), chromosome aberrations (CA), and DNA damage using the comet assay were analyzed. MI in human peripheral blood lymphocyte cultures treated with 1, 10, 100, and 1,000 μg mL⁻¹ cis-[RuCl₂(NH₃)₄]Cl were 5.9%, 4.6%, 3.9%, and 0%, respectively. Doxorubicin chloridate was used as the positive control. CA derived from 1, 10, and 100 μg mL⁻¹ concentrations were defined as spontaneous when compared with the negative control, and at the concentration of 1,000 μg mL⁻¹, the cell cycle was inhibited (IM = 0%). Results obtained for the comet assay using cis-[RuCl₂(NH₃)₄]Cl suggest that this compound has no genotoxic activity against cultured human peripheral blood lymphocytes.     

Enhancement of specific nitrogenase activity inAzospirillum brasilense andKlebsiella pneumoniae,inhibition inRhizobium japonicum under air by phenol

Specific nitrogenase activity inAzospirillum brasilense ATCC 29145 in surface cultures under air is enhanced from about 50 nmol C₂H₄·mg protein^-1·h^-1 to 400 nmol C₂H₄ by the addition of 1 mM phenol. 0.5 and 2 mM phenol added increase the rate 5-fold and 4-fold. This enhancement effect is observed only between 2 and 3 days after inoculation, with only a small reduction of the growth of the cells by the phenol added. In surface cultures under 1% O₂, nitrogenase activity is slightly reduced by the addition of 1–0.01 mM phenol. Utilization of succinate is enhanced during the period of maximum enhancement of nitrogenase activity by 60% by addition of 1 mM phenol. The cells did not produce¹⁴CO₂ from [U-¹⁴C] phenol, neither in surface cultures nor in liquid cultures and less than 0.1% of the phenol was incorporated into the cells. A smaller but significant enhancement of nitrogenase activity by about 100% in surface cultures under air was found withKlebsiella pneumoniae K 11 after addition of 1 mM phenol. However, inRhizobium japonicum 61-A-101 all phenol concentrations above 0.01 mM reduced nitrogenase activity. With 1 mM phenol added activity was reduced to less than 10% with no effect on the growth in the same cultivation system. With thisRhizobium japonicum strain significant quantities of phenol (25 mol in 24 h by 2·10¹² cells) were metabolized to¹⁴CO₂, with phenol as sole carbon source. WithAzospirillum brasilense in liquid culture under 1% and 2% O₂ in the gas phase, no enhancement of nitrogenase activity by phenol was noticed.     

Oxidation of amines by yeasts grown on 1-aminoalkanes or putrescine as the sole source of carbon,nitrogen and energy

The maximum growth rate of Trichosporon cutaneum CBS 8111 in chemostat cultures was 0.185 h^-1 on ethylamine and 0.21 h^-1 on butylamine, that of Candida famata CBS 8109 was 0.32 h^-1 on putrescine.The amine oxidation pattern of the ascomycetous strains studied, viz. Candida famata CBS 8109, Stephanoascus ciferrii CBS 4856 and Trichosporon adeninovorans CBS 8244 was independent of the amine that had been used as the growth substrate. It resembled that of benzylamine/putrescine oxidase found in other ascomycetous yeasts. However, differences in pH optimum and substrate specificity were observed between the amine-oxidizing systems of these three species.The amine oxidation pattern of cell-free extracts of Trichosporon cutaneum CBS 8111 varied with the amine that was used as growth substrate. The enzyme system produced by Cryptococcus laurentii CBS 7140 failed to oxidize isobutylamine and benzylamine, and showed a high pH optimum.The synthesis of amine oxidase in the four yeast strains studied was not repressed by ammonium chloride and was weakly repressed by glucose but was strongly repressed if both compounds were present in the growth medium.     

Biodegradation of phenol and <Emphasis Type="Italic">m</Emphasis>-cresol by <Emphasis Type="Italic">Candida albicans</Emphasis> PDY-07 under anaerobic condition

Strain Candida albicans PDY-07 was used to study the anaerobic biodegradation of phenol and m-cresol as single and dual substrates in batch cultures. The strain had a higher potential to degrade phenol than m-cresol. The cell growth kinetics of batch cultures with various initial m-cresol concentrations was investigated, and the Haldane kinetic model adequately described the dynamic behavior of cell growth on m-cresol. When cells grew on the mixture of phenol and m-cresol, substrate interactions were observed. Phenol inhibited the utilization of m-cresol; on the other hand, m-cresol also inhibited the degradation of phenol. However, the presence of low-concentration phenol enhanced m-cresol biodegradation; 100 mg/l m-cresol could be completely degraded within a shorter period of time than m-cresol alone in the presence of 150–300 mg/l phenol. The maximum m-cresol biodegradation rate was obtained at the existence of 200 mg/l phenol. Phenol was preferably utilized by the strain as a carbon and energy source. In addition, a sum kinetics model was used to describe the cell growth behavior in binary mixture of phenol and m-cresol, and the interaction parameters were determined. The model adequately predicted the growth kinetics and the interaction between the substrates.     

Growth and laccase production kinetics of <Emphasis Type="Italic">Trametes versicolor</Emphasis> in a stirred tank reactor

White rot fungi are a promising option to treat recalcitrant organic molecules, such as lignin, polycyclic aromatic hydrocarbons, and textile dyes, because of the lignin-modifying enzymes (LMEs) they secrete. Because knowledge of the kinetic parameters is important to better design and operate bioreactors to cultivate these fungi for degradation and/or to produce LME(s), these parameters were determined using Trametes versicolor ATCC 20869 (ATCC, American Type Culture Collection) in a magnetic stir bar reactor. A complete set of kinetic data has not been previously published for this culture. Higher than previously reported growth rates with high laccase production of up to 1,385 U l⁻¹ occurred during growth without or glucose limitation. The maximum specific growth rate averaged 0.94 ± 0.23 day⁻¹, whereas the maximum specific substrate consumption rates for glucose and ammonium were 3.37 ± 1.16 and 0.15 ± 0.04 day⁻¹, respectively. The maximum specific oxygen consumption rate was 1.63 ± 0.36 day⁻¹.     

Heterologous expression of polyhydroxyalkanoate depolymerase from <Emphasis Type="Italic">Thermobifida</Emphasis> sp. in <Emphasis Type="Italic">Pichia pastoris</Emphasis> and catalytic analysis by surface plasmon resonance

A polyhydroxyalkanote depolymerase gene from Thermobifida sp. isolate BCC23166 was cloned and expressed as a C-terminal His₆-tagged fusion in Pichia pastoris. Primary structure analysis revealed that the enzyme PhaZ-Th is a member of a proposed new subgroup of SCL-PHA depolymerase containing a proline–serine repeat linker. PhaZ-Th was expressed as two glycosylated forms with apparent molecular weights of 61 and 70 kDa, respectively. The enzyme showed esterase activity toward p-nitrophenyl alkanotes with V _max and K _m of 3.63 ± 0.16 μmol min⁻¹ mg⁻¹ and 0.79 ± 0.12 mM, respectively, on p-nitrophenyl butyrate with optimal activity at 50–55°C and pH 7–8. Surface plasmon resonance (SPR) analysis demonstrated that PhaZ-Th catalyzed the degradation of poly-[(R)-3-hydroxybutyrate] (PHB) films, which was accelerated in (R)-3-hydroxyvalerate copolymers with a maximum degradation rate of 882 ng cm⁻² h⁻¹ for poly[(R)-3-hydroxybutyrate-co-3-hydroxyvalerate] (12 mol% V). Surface deterioration, especially on the amorphous regions of PHB films was observed after exposure to PhaZ-Th by atomic force microscopy. The use of P. pastoris as an alternative recombinant system for bioplastic degrading enzymes in secreted form and a sensitive SPR analytical technique will be of utility for further study of bioplastic degradation.     

Quasi steady state growth of <Emphasis Type="Italic">Lactococcus lactis</Emphasis> in glucose-limited acceleration stat (A-stat) cultures

Quasi steady state growth of Lactococcus lactis IL 1403 was studied in glucose-limited A-stat cultivation experiments with acceleration rates (a) from 0.003 to 0.06 h⁻² after initial stabilization of the cultures in chemostat at D = 0.2–0.3 h⁻¹. It was shown that the high limit of quasi steady state growth rate depended on the acceleration rate used—at an acceleration rate 0.003 h⁻² the quasi steady state growth was observed until μ _crit = 0.59 h⁻¹, which is also the μ _max value for the culture. Lower values of μ _crit were observed at higher acceleration rates. The steady state growth of bacteria stabilized at dilution rate 0.2 h⁻¹ was immediately disrupted after initiating acceleration at the highest acceleration rate studied—0.06 h⁻². Observation was made that differences [Δ(μ − D)] of the specific growth rates from pre-programmed dilution rates were the lowest using an acceleration rate of 0.003 h⁻² (< 4% of preset changing growth rate). The adaptability of cells to follow preprogrammed growth rate was found to decrease with increasing dilution rate—it was shown that lower acceleration rates should be applied at higher growth rates to maintain the culture in the quasi steady state. The critical specific growth rate and the biomass yields based on glucose consumption were higher if the medium contained S ₀ = 5 g L⁻¹ glucose instead of S ₀ = 10 g L⁻¹. It was assumed that this was due to the inhibitory effect of lactate accumulating at higher concentrations in the latter cultures. Parallel A-stat experiments at the same acceleration and dilution rates showed good reproducibility—Δ(μ − D) was less than 5%, standard deviations of biomass yields per ATP produced (Y _ATP), and biomass yields per glucose consumed (Y _XS) were less than 15%.     

Molecular cloning, genetic organization of gene cluster encoding phenol hydroxylase and catechol 2,3-dioxygenase in Alcaligenes faecalis IS-46

Alcaligenes faecalis IS-46 can utilize phenol as the sole carbon and energy source at concentration up to 1000 mg/l. In this report we created a cosmid library of this strain and the two clones specifying the whole L-46d type of phenol hydroxylase gene cluster were identified and characterized. Sequence analysis revealed that although the overall gene organization of the clusters was quite similar, few coding sequences differed or were found to have two copies compared with other source organisms. One of these coding sequences showed a good protein sequence similarity to a hypothetical protein and one matched with a regulatory protein of the LysR system. Their putative role in phenol degradation was discussed. Bioinformatic analysis suggested tentative phylogenetic assignments of the retrieved clusters. This work described for first time the complete nucleotide sequence and genetic organization of the whole phenol hydroxylase gene cluster in A. faecalis species.     

Biotreatment of phenol-contaminated wastewater in a spiral packed-bed bioreactor

A spiral packed-bed bioreactor inoculated with microorganisms obtained from activated sludge was used to conduct a feasibility study for phenol removal. The reactor was operated continuously at various phenol loadings ranging from 53 to 201.4 g m⁻³ h⁻¹, and at different hydraulic retention times (HRT) in the range of 20–180 min to estimate the performance of the device. The results indicated that phenol removal efficiency ranging from 82.9 to 100% can be reached when the reactor is operated at an HRT of 1 h and a phenol loading of less than 111.9 g m⁻³ h⁻¹. At an influent phenol concentration of 201.4 g m⁻³, the removal efficiency increased from 18.6 to 76.9% with an increase in the HRT (20–120 min). For treatment of phenol in the reactor, the maximum biodegradation rate (V _m) was 1.82 mg l⁻¹ min⁻¹; the half-saturation constant (K _s), 34.95 mg l⁻¹.     

Phenol biodegradation by the thermoacidophilic archaeon <Emphasis Type="Italic">Sulfolobus solfataricus</Emphasis> 98/2 in a fed-batch bioreactor

Toxic at low concentrations, phenol is one of the most common organic pollutants in air and water. In this work, phenol biodegradation was studied in extreme conditions (80°C, pH = 3.2) in a 2.7 l bioreactor with the thermoacidophilic archaeon Sulfolobus solfataricus 98/2. The strain was first acclimatized to phenol on a mixture of glucose (2000 mg l⁻¹) and phenol (94 mg l⁻¹) at a constant dissolved oxygen concentration of 1.5 mg l⁻¹. After a short lag-phase, only glucose was consumed. Phenol degradation then began while glucose was still present in the reactor. When glucose was exhausted, phenol was used for respiration and then for biomass build-up. After several batch runs (phenol < 365 mg l⁻¹), specific growth rate (μ_X) was 0.034 ± 0.001 h⁻¹, specific phenol degradation rate (q_P) was 57.5 ± 2 mg g⁻¹ h⁻¹, biomass yield (Y_X/P) was 52.2 ± 1.1 g mol⁻¹, and oxygen yield factor ( \textY_{\textX/\textO 2} ) \left( {{\text{Y}}_{{{\text{X}}/{\text{O}}_{ 2} }} } \right) was 9.2 ± 0.2 g mol⁻¹. A carbon recovery close to 100% suggested that phenol was exclusively transformed into biomass (35%) and CO₂ (65%). Molar phenol oxidation constant ( \textY_{\textO 2 /\textP} ) \left( {{\text{Y}}_{{{\text{O}}_{ 2} /{\text{P}}}} } \right) was calculated from stoichiometry of phenol oxidation and introducing experimental biomass and CO₂ conversion yields on phenol, leading to values varying between 4.78 and 5.22 mol mol⁻¹. Respiratory quotient was about 0.84 mol mol⁻¹, very close to theoretical value (0.87 mol mol⁻¹). Carbon dioxide production, oxygen demand and redox potential, monitored on-line, were good indicators of growth, substrate consumption and exhaustion, and can therefore be usefully employed for industrial phenol bioremediation in extreme environments.     

trans-Stilbene degradation by Arthrobacter sp. SL3 cells

trans-Stilbene degradation was examined by the reaction using resting cells of microorganisms isolated through the enrichment culture using trans-stilbene. The strain SL3, showing the highest trans-stilbene-degrading activity, was identified as Arthrobacter sp. One of the reaction products was identified to be cis,cis-muconic acid. Arthrobacter sp. SL3 cells also transformed benzaldehyde, benzoic acid and catechol into cis,cis-muconic acid, suggesting that one benzene ring of trans-stilbene was converted into cis,cis-muconic acid via benzaldehyde formed by its C_α=C_β bond cleavage.     

Optimization of activated carbon fiber preparation from Kenaf using K2HPO4 as chemical activator for adsorption of phenolic compounds

The present work reports the preparation of activated carbon fiber (ACF) from Kenaf natural fibers. Taguchi experimental design method was used to optimize the preparation of ACF using K₂HPO₄. Optimized conditions were: carbonization at 300 °C, impregnation with 30% w/v K₂HPO₄ solution and activation at 700 °C for 2 h with the rate of achieving the activation temperature equal to 2 °C min⁻¹. The surface characteristics of the ACF prepared at optimized conditions were also studied using pore structure analysis, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Pore structure analysis shows that micropores constitute the most of the porosity of the prepared ACF. The ability of the ACF prepared at optimized conditions to adsorb phenol and p-nitrophenol from aqueous solution was also investigated. The equilibrium data of phenol and p-nitrophenol adsorption on the prepared ACF were well fitted to the Langmuir isotherm. The maximum adsorption capacities of phenol and p-nitrophenol on the prepared ACF are 140.84 and 136.99 mg g⁻¹, respectively. The adsorption process follows the pseudo-first-order kinetic model.