Degradation Rate Coefficients Research Articles

In situ biodecolorization kinetics of Acid Red 66 in aqueous solutions by Trametes versicolor

The biological decolorization methodology and the mechanism involved in the degradation of Acid Red 66 was chosen as a model of azo dye using the white rot fungi Trametes versicolor was studied. Biodecolorization of Acid Red 66 using white rot fungi T. versicolor was demonstrated by the decolorization of the culture medium, the extent of which was determined by monitoring the decrease in absorbance at 506 nm. The biodecolorization kinetics of Acid Red 66 (100 ppm) was found to be first order and the degradation rate coefficient is 1.312 × 10 −2 min −1 ( R = 0.96683, n = 8) at 30 °C. The effects of independent variables such as carbon sources, nitrogen sources pH, and temperature on the biodecolorization of Acid Red 66 was also investigated.

Photocatalytic and Thermal Degradation of Poly(methyl methacrylate), Poly(butyl acrylate), and Their Copolymers

The photocatalytic and thermal degradations of poly(methyl methacrylate), poly(butyl acrylate), and their copolymers of different compositions were studied. The photocatalytic degradation was investigated in o-dichlorobenzene in the presence of two different catalysts, namely, Degussa P-25 and combustion synthesized nanotitania (CSN-TiO2). The samples were analyzed by using gel permeation chromatography (GPC) to obtain the molecular weight distributions (MWDs) as a function of reaction time. Experimental data indicated that the photodegradation of these polymers occurs by both random and chain end scission. A continuous distribution kinetic model was used to determine the degradation rate coefficients by fitting the experimental data with the model. Both the random and specific rate coefficients of the copolymers decreased with increasing percentage of butyl acrylate (BA). Thermal degradation of the copolymers was investigated by thermogravimetry. The normalized weight loss profiles for the copolymers showed that the thermal stability of the copolymers increased with mole percentage of BA in the copolymer (PMMABA). The Ozawa method was used to determine the activation energies at different conversions. At low acrylate content in the copolymer, the activation energy depends on conversion, indicating multiple degradation mechanisms. At high acrylate content in the copolymer, the activation energy is independent of conversion, indicating degradation by a one-step mechanism.

Bench-scale ozonation study of waste activated sludge

A bench-scale ozonation study was conducted on waste activated sludge (WAS) in a 10-L, clear PVC, semi-batch, bubble column reactor. Two separate runs were performed on 5-L samples of WAS obtained from the Rocky Creek Wastewater Treatment Plant (WWTP) in Macon, Georgia. The Rocky Creek facility uses the extended aeration activated sludge process to treat domestic wastewater. Ozone was sparged through a porous diffuser at an application rate of 0.0525 mg O3 min− 1 at contact times of 9 days and 12 days, respectively, during Runs #1 and #2. Parameters that were monitored during the study included: alkalinity, ammonia, conductivity, nitrite, nitrate, pH, phosphate, solids degradation rate coefficient (KD), soluble chemical oxygen demand (SCOD), total chemical oxygen demand (TCOD), total dissolved solids (TDS), total solids (TS), total volatile solids (TVS), turbidity, and unstirred sludge volume index (SVIu). Ozone was very effective at removing TCOD and TS. TCOD removals were 43% and 99% respectively for Runs #1 and #2. Total solids removal during Runs #1 and #2 was 50% and 95%, respectively. The degradation rate coefficient (KD) based on VSS was 0.17 days− 1 and 0.54 days− 1 for Runs #1 and #2. Both the nitrate and phosphate concentrations increased as ozone contact time increased during each run. The unstirred SVI decreased with an increase in ozone contact time, however, extended ozonation caused the SVI to increase. Actual ozone dosages for Runs #1 and #2 were 0.0036 and 0.011 mg O3 per mg TS removed.

Estimation of Sequential Degradation Rate Coefficients for Chlorinated Ethenes

A sequential anaerobic-aerobic bioremediation pilot test was performed to assess its viability for chlorinated ethenes and to determine scaling parameters for remedial design. Transect data were evaluated to determine the first-order degradation rate of trichloroethene (TCE). Because the Damkohler numbers were greater than unity, a single-well regression approach was used to estimate the sequential first-order degradation rates. The biostimulated degradation kinetics were influenced by competing electron acceptors and total organic carbon. First-order degradation kinetics were appropriate after the biomass population was stimulated and critical redox conditions were established. First-order degradation rate coefficients ( λ ) were calculated for the anaerobic and aerobic degradation of TCE, cis-1,2-dichloroethene (cDCE), and vinyl chloride (VC) using regression analyses from predominant daughter products. In anaerobic groundwater, λTCE =0.084 days−1 , λcDCE =0.037 days−1 , and λVC =0.046 days−1 adjacent t...

Effect of Oxidizers on Microwave-Assisted Oxidative Degradation of Poly(alkyl acrylates)

The effect of oxidizers on the microwave-assisted oxidative degradation kinetics of poly(alkyl acrylates), namely, poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA), and poly(butyl acrylate) (PBA), was studied. The molecular weight distributions were measured by gel permeation chromatography, and continuous distribution kinetic models were used to determine the degradation rate coefficients. The effect of alkyl group substituents on the microwave-assisted oxidative degradation of poly(alkyl acrylates) was also investigated. The degradation rate of poly(alkyl acrylates) decreased with an increase in the number of carbon atoms of the alkyl substituents and thus followed the order PMA > PEA > PBA, while the activation energy increased with the length of alkyl group substituents. The rate coefficients of hydrogen abstraction and oxidative random chain scission were found to be independent of the oxidizer and dependent only on the nature of the polymer. The differences in the overall degradation rate of poly(ethyl acrylate) in the presence of different oxidizing agents were only dependent on the rate of oxidizer dissociation. This is the first study that shows that the degradation rate of the polymer in the presence of any oxidizer can be predicted by knowing only the thermal dissociation rate constant values of the oxidizer, which can be easily obtained from existing literature.

Kinetics of the ultrasonic degradation of poly (alkyl methacrylates)

The influence of the alkyl group substituents on the ultrasonic degradation of poly (alkyl methacrylate)s, namely poly (methyl methacrylate) (PMMA), poly (ethyl methacrylate) (PEMA) and poly (butyl methacrylate) (PBMA) was studied. The rate coefficient increased with an increase in the number of carbon atoms in the alkyl group: thus the order of degradation was PBMA > PEMA > PMMA. This was attributed to the scission of the main chain, which increases with the length of the side chain. The ultrasonic degradation of PBMA was investigated in various solvents, at different temperatures and at different ultrasound intensities. The degradation rate coefficients increased logarithmically with the decrease in vapor pressure and increased linearly with an increase in viscosity of the solvent and ultrasound intensity. The effect of three different initiators, benzoyl peroxide (BPO), dicumyl peroxide (DCP) and azo-bisisobutyronitrile (AIBN) on the ultrasonic degradation of PBMA was also studied. The degradation of the polymer decreased in the presence of the initiator. A continuous distribution model was developed for the radical mechanism involved in degradation and was used to determine the degradation rate coefficients of PBMA in presence of initiator. The model indicated that the degradation rate coefficient of the interaction of the PBMA radical with the initiator is independent of the dissociation constant of the initiator.

Thermal and Photocatalytic Degradation of Poly(methyl methacrylate), Poly(butyl methacrylate), and Their Copolymers

The photocatalytic degradation of the homopolymers, poly(methyl methacrylate) (PMMA), poly(butyl methacrylate) (PBMA), and their copolymers (PMMABMA) was studied in o-dichlorobenzene in the presence of commercial TiO2 (Degussa P-25) and TiO2 synthesized by combustion synthesis (CSN-TiO2). Gel permeation chromatography was used to determine the evolution of molecular weight distributions with reaction time. The experimental data indicated that the polymers PMMA and PBMA and their copolymers degrade by simultaneous random and chain end scission. A continuous distribution model was developed for the mechanism involved in degradation by both random and chain end scission and used to determine the degradation rate coefficients. The degradation rate coefficients of the polymers in the presence of CSN-TiO2 were higher than the degradation rate coefficients obtained with commercial TiO2 (Degussa P-25). The degradation rate coefficient of copolymers was in between that of the homopolymers and increased linearly with the increase of mol % of PMMA. The degradation of PMMA, PBMA, and their copolymers was also investigated by thermogravimetric analysis. The copolymers exhibited better thermal stability than the homopolymers in contrast to that observed for photocatalytic degradation.

Degradation of polycaprolactone in supercritical fluids

The degradation of polycaprolactone (PCL) was studied in subcritical and supercritical toluene from 250 to 375 °C at 50 bar. The degradation was also investigated in various solvents like ethylbenzene, o-xylene and benzene at 325 °C and 50 bar. The effect of pressure on degradation was also evaluated at 325 °C at various pressures (35, 50 and 80 bar). The variation of molecular weight with time was analyzed using gel permeation chromatography and modeled using continuous distribution kinetics to evaluate the degradation rate coefficients. PCL degrades by random chain scission in subcritical conditions (250–300 °C) and by chain end scission (325–375 °C) in supercritical conditions in toluene. The degradation of PCL in other solvents at 325 °C was by chain end scission under both subcritical and supercritical conditions indicating that the mode of scission depends on the temperature and not on the supercriticality of the solvent. The thermogravimetric analysis of PCL was investigated at various heating rates (2–24 °C/min) and the activation energy was determined using Friedman, Ozawa and Kissinger methods. It was shown that PCL degrades by random scission at lower temperatures and by chain end scission at higher temperatures again indicating that the mode of scission is dependent on the temperature.

Efficient Reduction of Chitosan Molecular Weight by High-Intensity Ultrasound: Underlying Mechanism and Effect of Process Parameters

The degradation of chitosan by high-intensity ultrasound (HIU) as affected by ultrasound parameters and solution properties was investigated by gel permeation chromatography coupled with static light scattering. The molecular weight, radius of gyration, and polydispersity of chitosan were reduced by ultrasound treatment, whereas chitosan remained in the same random coil conformation and the degree of acetylation did not change after sonication. The results demonstrate that (1) the degradation of chitosan by ultrasound is primarily driven by mechanical forces and the degradation mechanism can be described by a random scission model; (2) the degradation rate is proportional to M w (3); and (3) the degradation rate coefficient is affected by ultrasound intensity, solution temperature, polymer concentration, and ionic strength, whereas acid concentration has little effect. Additionally, the data indicate that the degradation rate coefficient is affected by the degree of acetylation of chitosan and independent of the initial molecular weight.

Spatial moment analysis of transport of nonlinearly adsorbing pesticides using analytical approximations

Analytical approximations were derived for solute transport of pesticides subject to Freundlich sorption, and first‐order degradation restricted to the liquid phase. Solute transport was based on the convection‐dispersion equation (CDE) assuming steady flow. The center of mass (first spatial moment) was approximated both for a non‐degraded solute pulse and for a pulse degraded in the liquid phase. The remaining mass (zeroth spatial moment) of a linearly sorbing solute degraded in the liquid phase was found to be a function of only the center of mass (first spatial moment) and the Damköhler number (i.e., the product of degradation rate coefficient and dispersivity divided by flow velocity). This relationship between the zeroth and first spatial moments was shown to apply to nonlinearly sorbing pulses as well. The mass fraction leached of a pesticide subject to Freundlich sorption and first‐order degradation in the solution phase only was found to be a function of the Damköhler number and of the dispersivity, so independent of sorption. Hence perceptions of the effects of sorption on pesticide leaching should be reconsidered. These conclusions equally hold for other micropollutants that degrade in the solution phase only.

Opinion on a request from EFSA related to the default Q10 value used to describe the temperature effect on transformation rates of pesticides in soil - Scientific Opinion of the Panel on Plant Protection Products and their Residues (PPR Panel)

SUMMARY One factor affecting the degradation rate of chemicals (including plant protection products) is temperature. It is generally accepted that this dependency may be reasonably described by using the Arrhenius equation which gives the degradation rate coefficient as a function of the temperature and the activation energy Ea. Using this Ea value, the ratio of degradation rates between two temperatures can be calculated. The ratio between the rates at 20° and 10°C is usually written as the Q10 value. This value is used in environmental exposure assessment to account for the impact of different temperatures. As a default, the value of Q10 = 2.2 was proposed by FOCUS (1997). The Panel on Plant Protection Products and their Residues (PPR Panel) of the European Food Safety Authority (EFSA) issued an Opinion on the Q10 value in 2006.

Attenuation of Fluorocarbons Released from Foam Insulation in Landfills

Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs) have been used as blowing agents (BAs) for foam insulation in home appliances and building materials, which after the end of their useful life are disposed of in landfills. The objective of this project was to evaluate the potential for degradation of BAs in landfills, and to develop a landfill model, which could simulate the fate of BAs in landfills. The investigation was performed by use of anaerobic microcosm studies using different types of organic waste and anaerobic digested sludge as inoculum. The BAs studied were CFC-11, CFC-12, HCFC-141b, HFC-134a, and HFC-245fa. Experiments considering the fate of some of the expected degradations products of CFC-11 and CFC-12 were included like HCFC-21, HCFC-22, HCFC-31, HCFC-32, and HFC-41. Degradation of all studied CFCs and HCFCs was observed regardless the type of waste used. In general, the degradation followed first-order kinetics. CFC-11 was rapidly degraded from 590 microg L(-1) to less than 5 microg L(-1) within 15-20 days. The degradation pattern indicated a sequential production of HCFC-21, HCFC-31, and HFC-41. However, the production of degradation products did not correlate with a stoichiometric removal of CFC-11 indicating that other degradation products were produced. HCFC-21 and HCFC-31 were further degraded whereas no further degradation of HFC-41 was observed. The degradation rate coefficient was directly correlated with the number of chlorine atoms attached to the carbon. The highest degradation rate coefficient was obtained for CFC-11, whereas lower rates were seen for HCFC-21 and HCFC-31. Equivalent results were obtained for CFC-12. HCFC-141b was also degraded with rates comparable to HCFC-21 and CFC-12. Anaerobic degradation of the studied HFCs was not observed in any of the experiments within a run time of up to 200 days. The obtained degradation rate coefficients were used as input for an extended version of an existing landfill fate model incorporating a time dependent BA release from co-disposed foam insulation waste. Predictions with the model indicate that the emission of foam released BAs may be strongly attenuated by microbial degradation reactions. Sensitivity analysis suggests that there is a need for determination of degradation rates under more field realistic scenarios.

Dynamic fate modeling of γ-hexachlorocyclohexane in the lower reaches of the Liao River

A QWASI model dependent on temperature is parameterized to describe the long-term fate of persistent organic pollutants (POPs) in the Liao River. The model parameters, namely fugacity capacity, degradation rate, and transfer coefficient, are profoundly affected by temperature. This model is used to simulate the fate of γ-hexachlorocyclohexane (γ-HCH) in the lower reaches of the Liao River from 1998 to 2008. Modeling results show that γ-HCH fugacity capacities in air, water, and sediment increase as temperature decreases, and the transfer and transformation rate coefficients increase as temperature increases. The variations of transfer and transformation parameter D values depend on fugacity capacities, and transfer and transformation coefficients simultaneously. The performance of the model is evaluated by comparing the predicted and observed concentrations in the water and sediment of the Liao River. The predicted values agree well with the observed value in the order of magnitude, in most cases within the factor of 3. It is believed that the model is appropriate for simulating the long term fate of POPs in the Liao River.

Transcriptional regulatory network refinement and quantification through kinetic modeling, gene expression microarray data and information theory.

BackgroundGene expression microarray and other multiplex data hold promise for addressing the challenges of cellular complexity, refined diagnoses and the discovery of well-targeted treatments. A new approach to the construction and quantification of transcriptional regulatory networks (TRNs) is presented that integrates gene expression microarray data and cell modeling through information theory. Given a partial TRN and time series data, a probability density is constructed that is a functional of the time course of transcription factor (TF) thermodynamic activities at the site of gene control, and is a function of mRNA degradation and transcription rate coefficients, and equilibrium constants for TF/gene binding.ResultsOur approach yields more physicochemical information that compliments the results of network structure delineation methods, and thereby can serve as an element of a comprehensive TRN discovery/quantification system. The most probable TF time courses and values of the aforementioned parameters are obtained by maximizing the probability obtained through entropy maximization. Observed time delays between mRNA expression and activity are accounted for implicitly since the time course of the activity of a TF is coupled by probability functional maximization, and is not assumed to be proportional to expression level of the mRNA type that translates into the TF. This allows one to investigate post-translational and TF activation mechanisms of gene regulation. Accuracy and robustness of the method are evaluated. A kinetic formulation is used to facilitate the analysis of phenomena with a strongly dynamical character while a physically-motivated regularization of the TF time course is found to overcome difficulties due to omnipresent noise and data sparsity that plague other methods of gene expression data analysis. An application to Escherichia coli is presented.ConclusionMultiplex time series data can be used for the construction of the network of cellular processes and the calibration of the associated physicochemical parameters. We have demonstrated these concepts in the context of gene regulation understood through the analysis of gene expression microarray time series data. Casting the approach in a probabilistic framework has allowed us to address the uncertainties in gene expression microarray data. Our approach was found to be robust to error in the gene expression microarray data and mistakes in a proposed TRN.

Assessment of Intrinsic Bioremediation of a Coal‐Tar‐Affected Aquifer Using Two‐Dimensional Reactive Transport and Biogeochemical Mass Balance Approaches

Expedited site characterization and groundwater monitoring using direct-push technology and conventional monitoring wells were conducted at a former manufactured gas plant site. Biogeochemical data and heterotrophic plate counts support the presence of microbially mediated remediation. By superimposing solutions of a two-dimensional reactive transport analytical model, first-order degradation rate coefficients ((day-1) ) of various compounds for the dissolved-phase plume were estimated (i.e., benzene [0.0084], naphthalene [0.0058], and acenaphthene [0.0011]). The total mass transformed by aerobic respiration, nitrate reduction, and sulfate reduction around the free-phase coal-tar dense-nonaqueous-phase-liquid region and in the plume was estimated to be approximately 4.5 kg/y using a biogeochemical mass-balance approach. The total mass transformed using the degradation rate coefficients was estimated to be approximately 3.6 kg/y. Results showed that a simple two-dimensional analytical model and a biochemical mass balance with geochemical data from expedited site characterization can be useful for rapid estimation of mass-transformation rates.

Biodegradation of hydrocarbons vapors: Comparison of laboratory studies and field investigations in the vadose zone at the emplaced fuel source experiment, Airbase Værløse, Denmark

The natural attenuation of volatile organic compounds (VOCs) in the unsaturated zone can only be predicted when information about microbial biodegradation rates and kinetics are known. This study aimed at determining first-order rate coefficients for the aerobic biodegradation of 13 volatile petroleum hydrocarbons which were artificially emplaced as a liquid mixture during a field experiment in an unsaturated sandy soil. Apparent first-order biodegradation rate coefficients were estimated by comparing the spatial evolution of the resulting vapor plumes to an analytical reactive transport model. Two independent reactive numerical model approaches have been used to simulate the diffusive migration of VOC vapors and to estimate degradation rate coefficients. Supplementary laboratory column and microcosm experiments were performed with the sandy soil at room temperature under aerobic conditions. First-order kinetics adequately matched the lab column profiles for most of the compounds. Consistent compound-specific apparent first-order rate coefficients were obtained by the three models and the lab column experiment, except for benzene. Laboratory microcosm experiments lacked of sensitivity for slowly degrading compounds and underestimated degradation rates by up to a factor of 5. Addition of NH 3 vapor was shown to increase the degradation rates for some VOCs in the laboratory microcosms. All field models suggested a significantly higher degradation rate for benzene than the rates measured in the lab, suggesting that the field microbial community was superior in developing benzene degrading activity.

Effect of Alkyl-Group Substituents on the Degradation of Poly(alkyl methacrylates) in Supercritical Fluids

The effect of alkyl group substituents on the degradation kinetics of poly(alkyl methacrylates)namely, poly(n-butyl methacrylate) (PBMA), poly(isopropyl methacrylate) (PPMA), poly(ethyl methacrylate) (PEMA), and poly(methyl methacrylate) (PMMA)under supercritical and subcritical conditions was studied at various temperatures (250−375 °C). The molecular-weight distributions were measured via gel permeation chromatography, and continuous distribution kinetic models were used to determine the degradation rate coefficients. The degradation rate coefficients under supercritical conditions were determined to be significantly higher than that those under subcritical conditions. The degradation rate of poly(alkyl methacrylates) increased as the number of carbon atoms of the alkyl substituents increased and, thus, followed the order PBMA > PPMA > PEMA > PMMA. The activation energy decreased with chain length under both subcritical and supercritical conditions. The degradation of PBMA was investigated at various pressures (20−85 bar) at a temperature of 325 °C, and the effect of pressure on the degradation rate coefficient was modeled using transition state theory. The degradation of PBMA was also investigated in different solvents at 325 °C and 60 bar. The supercritical state and the density of the solvent were determined to be important factors that influence the degradation kinetics.

Photodegradation of poly(vinyl alcohol) under UV and pulsed‐laser irradiation in aqueous solution

AbstractThe photodegradation of poly(vinyl alcohol) (PVA) in aqueous solution was investigated under UV exposure and pulsed‐laser irradiation. The degradation under UV exposure was studied at different pH values and with the addition of potassium chloride and potassium dichromate. The pulsed‐laser degradation of PVA was investigated with a Nd : YAG laser, operating at a wavelength of 266 nm with about 6‐ns pulses. The pulsed‐laser degradation was studied at different polymer concentrations and light intensities. Samples were analyzed by gel permeation chromatography. The degradation rate coefficients were determined by the application of a continuous distribution model. The photodegradation rates under UV exposure were highest at extremes of pH and were greatly enhanced by the addition of potassium chloride and potassium dichromate. The pulsed‐laser degradation of the polymer decreased with increasing polymer concentration, although a threshold light intensity was required to initiate the degradation process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 958–966, 2006

Effects of initial molecular weight on removal rate of dextran in biofilms

Degradation kinetics of different size dextrans in a biofilm reactor were evaluated. Degradation rates of dextran standards, measured as time series of oxygen utilisation rates, decreased with increasing initial molecular weight. Removal of bulk phase total organic carbon with time was highly correlated ( R 2>0.99) and could be modelled with variable half-order degradation rate expressions. A power correlation between initial molecular weight and the variable half-order degradation rate coefficient was found for polymers in the range 6–500 kDa. Degradation of dextran in the colloid size range ( M W>1 Mda) did not follow the same kinetics. Reductions in the observed removal rate with polymer size can be explained by the effect of reduced diffusivities of the substrate, without assuming reaction rate effects.

Effects of the pH, concentration, and solvents on the ultrasonic degradation of poly(vinyl alcohol)

AbstractThe ultrasonic degradation of poly(vinyl alcohol) was investigated at different pHs of the solvent, in different water/solvent binary mixtures, and at different polymer concentrations. The samples were analyzed with gel permeation chromatography. The degradation rate coefficients were determined with a continuous distribution model. A higher degradation rate was obtained at pH extremes, in better solvents, and at lower polymer concentrations. The results are explained and discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4888–4892, 2006