First-order Degradation Rate Constants Research Articles

Electropolymerization of aniline in acid media on the bare and chemically pre-treated aluminum electrodes: A comparative characterization of the polyaniline deposited electrodes

The electrosynthesis of polyaniline on the bare aluminum and pre-treated aluminum surface achieved in aqueous H 2PtCl 6 solution saturated with NaF for few seconds is described. The effect of some factors such as pre-treatment time, aniline and sulfuric acid concentrations on the electropolymerization process was investigated and optimum conditions were obtained. The stability of polyaniline film on the pre-treated aluminum electrode (Al–Pt) was studied as function of the potential imposed on the electrode. For applied electrode potentials of 0.1–0.7 V, the first-order degradation rate constant, k, of polyaniline film varies between 1 × 10 −6 and 2 × 10 −5 s −1, and a relatively low slope (i.e. 2.1) was obtained for the plot of log k versus E. The coatings were characterized by scanning electron microscopy (SEM), and cyclic voltammetric behavior of the polyaniline-deposited Al electrode (Al/PANI) and polyaniline-deposited Al–Pt electrode (Al–Pt/PANI) in 0.1 H 2SO 4 solutions is described. The electrocatalytic activity of the Al–Pt/PANI electrode against para-benzoquinone/hydroquinone (Q/H 2Q) and Fe(CN) 6 3−/Fe(CN) 6 4− redox systems was investigated and the obtained results are compared with those obtained on Al/PANI and bulk Pt electrodes.

Palladized aluminum as a novel substrate for electrosynthesis of polyaniline in sulfuric acid solutions

The electropolymerization of aniline on a palladized aluminum electrode (Pd/Al) by potentiodynamic as well as potentiostatic methods is described. The effect of the monomer concentration between 0.01 and 0.4 M on the polyaniline (PANI) formation and its growth on the Pd/Al electrode was investigated and a suitable concentration of 0.2 M is suggested. A similar study was carried out to investigate the effect of sulfuric acid concentration and 0.1 M sulfuric acid was chosen. A study on the influence of electropalladization time on the polymer formation and its growth suggested a convenient time of 40 s. The stability of the PANI film on the Pd/Al electrode was studied as function of the potential imposed on the electrode. For applied electrode potentials of 0.1–0.7 V, the first-order degradation rate constant, k, of PANI film varies between 1×10−6 and 2×10−5 s−1, and a relatively low slope (i.e., 2.2) was obtained for the plot of log k versus E. The coatings were characterized by scanning electron microscopy (SEM), and cyclic voltammetric behavior of the PANI-deposited Pd/Al electrode is discussed. The electrocatalytic activity of the PANI-deposited Pd/Al electrode against para-benzoquinone/hydroquinone (Q/H2Q) and % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX!% MathType!MTEF!2!1!+-% feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX% garmWu51MyVXgatuuDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wz% aebbnrfifHhDYfgasaacH8qrps0lbbf9q8WrFfeuY-Hhbbf9v8qqaq% Fr0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qq% Q8frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeWaeaaakeaada% WcgaqaaiaabAeacaqGLbWaaeWaaeaacaqGdbGaaeOtaaGaayjkaiaa% wMcaamaaDaaaleaacaaI2aaabaGaaG4maiabgkHiTaaaaOqaaiaabA% eacaqGLbWaaeWaaeaacaqGdbGaaeOtaaGaayjkaiaawMcaamaaDaaa% leaacaaI2aaabaGaaGinaiabgkHiTaaaaaaaaa!4681! $${{\text{Fe}}{\left( {{\text{CN}}} \right)}^{{3 - }}_{6} } \mathord{\left/ {\vphantom {{{\text{Fe}}{\left( {{\text{CN}}} \right)}^{{3 - }}_{6} } {{\text{Fe}}{\left( {{\text{CN}}} \right)}^{{4 - }}_{6} }}} \right. \kern-\nulldelimiterspace} {{\text{Fe}}{\left( {{\text{CN}}} \right)}^{{4 - }}_{6} }$$ redox systems were investigated and on the basis of % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX!% MathType!MTEF!2!1!+-% feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX% garmWu51MyVXgatuuDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wz% aebbnrfifHhDYfgasaacH8qrps0lbbf9q8WrFfeuY-Hhbbf9v8qqaq% Fr0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qq% Q8frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeWaeaaakeaacq% qHuoarcaWGfbWaaSbaaSqaaiaadchaaeqaaOGaeyypa0Jaamyramaa% DaaaleaacaWGWbaabaGaamyyaaaakiabgkHiTiaadweadaqhaaWcba% GaamiCaaqaaiaadogaaaaaaa!428E! $$\Delta E_{p} = E^{a}_{p} - E^{c}_{p} $$ of the corresponding cyclic voltammograms and the redox systems were identified as the reversible and quasi-reversible systems, respectively.

Influence of Network Structure on the Degradation of Photo-Cross-Linked PLA-b-PEG-b-PLA Hydrogels

Triblock copolymers of functionalized poly(lactic acid)-b-poly(ethylene glycol)-b-poly(lactic acid) (PLA-b-PEG-b-PLA) have been widely investigated as precursors for fabricating resorbable polymeric drug delivery vehicles and tissue engineering scaffolds. Previous studies show degradation and erosion behavior of PLA-b-PEG-b-PLA hydrogels to rely on macromer chemistry as well as structural characteristics of the cross-linked networks. In this research, the degradation kinetics of diacrylated PLA-b-PEG-b-PLA copolymers as soluble macromers and cross-linked gels are directly compared as a function of macromer concentration, buffer pH, and ionic strength. The pseudo first-order rate constants for degradation of soluble macromers increase with water concentration and show a minimum at intermediate pH values, but are insensitive to ionic strength. The degradation rate constants for covalently cross-linked gels display a greater sensitivity to local water concentration and a minimum at lower pH values than corresponding soluble macromers. In addition, ionic strength significantly affects the rate of gel degradation due to the direct correlation between the degree of network ionization and gel water content.

Isotopic Fractionation of Tetrachloroethene Undergoing Biodegradation Supported by Endogenous Decay

A long term column study of the anaerobic biodegradation and associated isotopic fractionation of tetrachloroethene and transformation products was conducted. The column, initially fed with tetrachloroethene, ethanol, and yeast extract, was operated for one year with input of dissolved tetrachloroethene only to examine reductive dehalogenation and isotopic fractionation under endogenous decay conditions. A one-dimensional, inverse, multispecies, reactive transport model was employed to estimate the degradation rate constants and enrichment factors of the chlorinated ethenes at different times and under different column conditions. The inverse method combined a genetic algorithm with a gradient-based method for efficient parameter estimation. The trichloroethene and cis-1,2-dichloroethene first-order degradation rate constants decreased with time as endogenous decay progressed in the absence of ethanol and yeast extract. Temporal trends in tetrachloroethene degradation rate constants were not significant. The enrichment factors did not change significantly with time, biodegradation rates, or readdition of ethanol at the end of the study. This is encouraging with respect to using isotope enrichment factors in reactive transport models to estimate the extent of biodegradation in the field.

Effect of precursor concentration on the characteristics of nanoscale zerovalent iron and its reactivity of nitrate

Differing precursor concentrations, 1.0, 0.1, and 0.01 M FeCl 3·6H 2O, were performed to produce nanoscale Fe 0 and the results were discussed in terms of the specific surface area, particle size and electrochemical properties. The results indicated that the nanoscale Fe 0 prepared by 0.01 M FeCl 3 had absolutely reduced in size (9–10 nm) and possessed the greatest specific surface area (56.67 m 2 g −1). These synthesized nanoscale Fe 0 particles were attempted to enhance the removal of 40 mg-N L −1 unbuffered nitrate solution. The first-order degradation rate constants ( k obs) increased significantly (5.5–8.6 times) with nanoscale Fe 0 prepared by 0.01 M precursor solution ( Fe 0.01 M 0 ) . When normalized to iron surface area concentration, the specific rate constant ( k SA) was increased by a factor of approximately 1.7–2.4 using Fe 0.01 M 0 (6.84×10 −4 L min −1 m −2 for Fe 0.01 M 0 , 4.04×10 −4 L min −1 m −2 for Fe 0.1 M 0 and 2.80×10 −4 L min −1 m −2 for Fe 1 M 0 ). The rise of reactivity of the reactive site on the Fe 0.01 M 0 surface was indicated by the specific rate constant ( k SA) calculation and the i 0 value of the electrochemical test.

In situ Raman spectroelectrochemical study of self-doped polyaniline degradation kinetics

The kinetics of electrochemical degradation for a self-doped sulfonated polyaniline derivative (a copolymer of aniline and m-aminobenzenesulfonic acid) has been studied with in situ Raman spectroscopy. It has been shown that the degradation proceeds faster in more acidic solutions. From the data obtained, first-order degradation rate constants have been calculated. Within the solution pH range of 0.5–9.0, first-order rate constants thus obtained vary, respectively, between (6.6 ± 0.8) × 10 −4 s −1 and (0.8 ± 0.1) × 10 −4 s −1 for electrode potential of 0.8 V vs. Ag/AgCl. A linear correlation between the degradation rate constant and solution pH has been found: log k = log k 0 + a · pH, where k represents rate constant at any pH (expressed in s −1), k 0 is the rate constant for pH 0, log k 0 = −3.09, and a = −0.11 is the slope of (log k, pH) dependence.

Degradation of pentachlorophenol in aqueous solution by audible-frequency sonolytic ozonation

The degradation of pentachlorophenol (PCP) in aqueous solution by audible-frequency sonolytic ozonation was studied. The sonolysis of H 2O and PCP/H 2O solutions and the dissolution and decomposition of ozone under audible-frequency sonication were evaluated as well. The results showed that the ozone dissolution rate and PCP degradation rate were significantly enhanced by sonication in comparison to using mechanical stirring and O 3 bubbling alone. This enhancement is most likely attributed to the strong turbulence induced by sonication. The first-order rate constant of PCP degradation by ozonation with sonication is more than 15 times faster than that with bubbling ozone alone, while the rate constant with mechanical stirring is only four times faster. The influence of the ozone feed rate on PCP degradation and the degradation byproducts were examined as well. In addition, results showed that no H 2O 2 was generated by sonolysis of water with audible-frequency sonication and no PCP was degraded by sonolysis alone.

Oxygen‐Enhanced Biodegradation of Phenoxy Acids in Ground Water at Contaminated Sites

The effects of adding oxygen to anaerobic aquifer materials on biodegradation of phenoxy acid herbicides were studied by laboratory experiments with aquifer material from two contaminated sites (a former agricultural machinery service and an old landfill). At both sites, the primary pollutants were phenoxy acids and related chlorophenols. It was found that addition of oxygen enhanced degradation of the six original phenoxy acids and six original chlorophenols. Inverse modeling on 14C 4-chloro-2-methylphenoxypropanoic acid (MCPP) degradation curves revealed that increasing the oxygen concentrations from <0.3 mg/L up to 7 to 8 mg/L shortened the lag phases (from approximately 150 d to 5 to 25 d) and increased first-order degradation rate constants by 1 order of magnitude (from approximately 5 x 10(-2) d(-1) to up to 30 x 10(-2) d(-1)). Additionally, the degree of MCPP mineralization was increased (30% to 50% mineralized at low oxygen concentrations and 50% to 70% mineralized at high oxygen concentrations, based on 14CO2 recovery). These positive effects on degradation were observed even at relatively low oxygen concentrations (2 mg/L). Furthermore, effects related to the addition of oxygen on the general geochemistry were studied. An oxygen consumption of 2.2 to 2.6 mg O2/g dw was observed due to oxidation of solid organic matter and, to some extent (0.5% to 11% of the total oxygen consumption), water-soluble compounds such as Fe2+, dissolved Mn, nonvolatile organic carbon, and NH4+. Overall, the results suggest that stimulated biodegradation by addition of oxygen might be a feasible remediation technology at herbicide-contaminated sites, although oxygen consumption by the sediment could limit the applicability.

Chemical reduction of an unbuffered nitrate solution using catalyzed and uncatalyzed nanoscale iron particles

Uncatalyzed and catalyzed nanoscale Fe 0 systems were employed for the denitrification of unbuffered 40 mg N L −1 nitrate solutions at initial neutral pH. Compared to microscale Fe 0 (<100 mesh), the efficiency and rate of nitrate removal using uncatalyzed and catalyzed nano-Fe 0 were highly promoted, in which the maximum promoted rate was obtained using copper-catalyzed nano-Fe 0 (nano-Cu/Fe). Nitrate first-order degradation rate constants ( k obs) decreased significantly (>70%) with aged nano-Fe 0 and aged nano-Cu/Fe, and were recovered with NaBH 4 as reductants at levels of about 85 and 75%, respectively. Activation energies ( E a) of nitrate reduction over the temperature range of 10–60 °C were 42.5 kJ mol −1 for microscale Fe 0, 25.8 kJ mol −1 for nano-Fe 0 and 16.8 kJ mol −1 for nano-Cu/Fe. Unlike microscale Fe 0, the kinetics of denitrification by nano-Fe 0 and nano-Cu/Fe began to show characteristics of mass transport in addition to chemical reaction control. Ammonium was the predominant end product in all the systems. However, as for nitrite, 40% of the degraded nitrate persisted in the nano-Cu/Fe system. Thus, relative to nano-Cu/Fe, nano-Fe 0 is a potential reductant for denitrification of groundwater as far as toxic nitrite generation is concern.

Use of 2,2?-Azobis(2-Amidinopropane) Dihydrochloride as a Reagent Tool for Evaluation of Oxidative Stability of Drugs

To study the oxidative degradation of drugs using a hydrophilic free radical initiator, 2,2'-Azobis(-amidinopropane) dihydrochloride (AAPH). AAPH was used as the free radical initiator to study oxidation of three model compounds (A, B, and C), which represent different oxidizable moieties. In the solution model, the drugs and AAPH were dissolved in a mixture of acetonitrile and aqueous buffer and incubated at elevated temperatures to evaluate oxidative degradation. The effects of pH and drug-AAPH ratio on the kinetics of the reaction were evaluated for compound A. Commonly used antioxidants were also evaluated by addition to solutions of drug and AAPH. In the solid-state model, blends of drug with microcrystalline cellulose were treated with AAPH and placed at elevated temperature and humidity to evaluate solid state oxidation. Use of AAPH resulted in selective oxidation of the model drugs by a free radical initiated process. The scope of the technique was further investigated in detail using compound A. The rate of oxidation of compound A varied directly with the concentration of AAPH. The pseudo first-order rate constants for the oxidative degradation were calculated from the kinetic data. The antioxidants were rank-ordered based on their quenching activity on the rates of AAPH initiated oxidation for compound A. The concept was extended to oxidation in solid state. The proposed AAPH model is useful in assessing oxidative stability of drug candidates in development.

Kinetic modeling of the radiolytic degradation of Acid Orange 7 in aqueous solutions

The degradation of Acid Orange 7 (AO7) in aqueous solutions induced by gamma-ray irradiation was investigated in terms of both the disappearance of parent molecule (decoloration) and the degree of mineralization. The disappearance of AO7 followed pseudo first-order kinetics, whereas its mineralization could be described by zero-order kinetics. The pseudo first-order degradation rate constants were found to be proportional to irradiation dose rates and the reciprocals of initial AO7 concentrations. Based on the experimental results and a reaction analysis on the steady-state radiolysis of aerated aqueous solutions, a kinetic model was developed for describing the radiolytic degradation of AO7. Moreover, with this kinetic model, the reaction rate constants of e(aq)(-) and H. with AO7 were estimated as 3.0 x 10(9) and 8.4 x 10(9) x L mol(-1) s(-1), respectively. Taking the relative contributions of oxidative and reductive species to AO7 degradation into account, oxidative radiolysis proved to be a better approach for the degradation of AO7.

Riboflavin‐ and cobalamin‐mediated biodegradation of chloroform in a methanogenic consortium

Chloroform (CF) is an important priority pollutant contaminating groundwater. Reductive dechlorination by anaerobic microorganisms is a promising strategy towards the remediation of CF. The objective of this study was to evaluate the use of redox active vitamins as electron shuttles to enhance the anaerobic biodegradation of CF in an unadapted methanogenic consortium not previously exposed to chlorinated compounds. Only negligible degradation of CF was observed in control cultures lacking redox active vitamins. The addition of riboflavin (RF), cyanocobalamin (CNB12), and hydroxycobalamin (HOB12) enabled biodegradation of CF. The reactions were predominantly catalyzed biologically as evidenced by the lack of any CF conversion in heat-killed controls amended with the cobalamins or minor conversion with RF. In live cultures, significant increases in the rate of CF conversion was observed at substoichiometric molar ratios as low as 0.1 to 0.01 vitamin:CF for RF and CNB12, respectively. At the highest molar vitamin:CF ratios tested of 0.2, the first-order rate constant of CF degradation was 5.3- and 91-fold higher in RF and CNB12 amended cultures, respectively, compared to the unamended control culture. The distribution of biotransformation products was highly impacted by the type of redox active vitamin utilized. Cultures supplemented with RF provided high yields of dichloromethane (DCM). On the other hand, cobalamins promoted the near complete mineralization of organochlorine in CF to inorganic chloride and lowered the yield of DCM. In cultures where no or little CF bioconversion occurred, prolonged exposure to CF resulted in cell lysis, as evidenced by the release of intracellular chloride. The results taken as a whole suggest that the anaerobic bioremediation of CF-contaminated sites can greatly be improved with strategies aimed at increasing the concentration of redox active vitamins.

Quantifying chlorinated ethene degradation during reductive dechlorination at Kelly AFB using stable carbon isotopes

Stable isotope analysis of chlorinated ethene contaminants was carried out during a bioaugmentation pilot test at Kelly Air Force Base (AFB) in San Antonio Texas. In this pilot test, cis-1,2-dichloroethene (cDCE) was the primary volatile organic compound. A mixed microbial enrichment culture, KB-1™, shown in laboratory experiments to reduce chlorinated ethenes to non-toxic ethene, was added to the pilot test area. Following bioaugmentation with KB-1™, perchloroethene (PCE), trichloroethene (TCE) and cDCE concentrations declined, while vinyl chloride (VC) concentrations increased and subsequently decreased as ethene became the dominant transformation product. Shifts in carbon isotopic values up to 2.7‰, 6.4‰, 10.9‰ and 10.6‰ were observed for PCE, TCE, cDCE and VC, respectively, after bioaugmentation, consistent with the effects of biodegradation. While a rising trend of VC concentrations and the first appearance of ethene were indicative of biodegradation by 72 days post-bioaugmentation, the most compelling evidence of biodegradation was the substantial carbon isotope enrichment (2.0‰ to 5.0‰) in ä 13C cDCE. Fractionation factors obtained in previous laboratory studies were used with isotope field measurements to estimate first-order cDCE degradation rate constants of 0.12 h −1 and 0.17 h −1 at 115 days post-bioaugmentation. These isotope-derived rate constants were clearly lower than, but within a factor of 2–4 of the previously published rate constant calculated in a parallel study at Kelly AFB using chlorinated ethene concentrations. Stable carbon isotopes can provide not only a sensitive means for early identification of the effects of biodegradation, but an additional means to quantify the rates of biodegradation in the field.

Optimization of nitrogen for bioventing of gasoline contaminated soil

Bioventing is a promising in situ remediation technology for hydrocarbon contaminated soil. Using low airflow rates to produce oxygen-rich conditions in the vadose zone, and nutrient addition, bioventing stimulates indigenous microorganisms that degrade the hydrocarbon contaminants. However, several questions about bioventing remain to be answered, including the optimum soil water content, type and amount of nutrients necessary, and contributions of different microbes. Experiments were conducted using small-scale respirometers containing gasoline-contaminated soil from an active remediation site to determine the effects of soil water content, nitrogen content, nitrogen form, and the composition of the microbial population on the gasoline biodegradation rate. Results indicate that optimum bioventing conditions were 18 wt.% soil water content, C:N = 10:1, using NH4+-N. A maximum first-order degradation rate constant of 0.12/d was observed. Biodegradation was limited at high C:N ratios by the availability of nitrogen and at low C:N ratios by acidification. It was also determined that aerobic bacteria were the dominant group responsible for biodegradation, with fungi playing a minor role. Key words: bioventing, degradation rate, nutrients, water content, scale-up, gasoline, microbial population.

Comparison treatment of various chlorophenols by electro-Fenton method: relationship between chlorine content and degradation

This study describes a comparative degradation of various chlorophenols by electro-Fenton method. Chloride released and reaction intermediate products were determined by ionic chromatography (IC) and gas chromatography/mass spectrometry (GC/MS). Using pentachlorophenol (PCP) as the model compound, we investigated the effects of cell voltage, electrolyte concentration and pH to optimize the degradation conditions. It was noted that the addition of small quantities of Fe 3+ or Fe 2+ significantly accelerated the degradation rate. Under the optimal conditions, electro-Fenton method was used to treat various chlorophenols including PCP, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and their mixture aqueous solutions. Their pseudo first-order degradation rate constants at the first stages were calculated and compared, which gave the following sequence: 2,4-DCP > 2,4,6-TCP > PCP > 4-CP. The relationship between the chlorine content and degradation rate was discussed and compared with other advanced oxidation processes. Finally, we proposed the degradation pathways of different chlorophenols.

Sonochemical removal of trihalomethanes from aqueous solutions

In this research, ultrasound irradiation was employed to degrade the trihalomethanes, THMs: CHCl 3, CHBrCl 2, CHBr 2Cl, CHBr 3, and CHI 3. The kinetics reaction rates and removal efficiencies of the THMs compounds, as a sole component in the aqueous solutions, were studied. Batch experiments were conducted at an ultrasonic frequency of 20 kHz and acoustic intensity of 3.75 W/cm 2. The first-order degradation rate constants and the sonolysis efficiencies followed the decreasing order of CHCl 3 > CHBrCl 2 > CHBr 2Cl > CHBr 3 > CHI 3. Up to 100% of the CHCl 3 was removed, while only 60% of the CHI 3 was sonodegraded, after 180 min sonication. The THMs vapor pressure was found to be the most important parameter affecting the sonodegradation kinetics and efficiency, while the bond dissociation energy and hydrophilic/hydrophobic characteristics of the THMs compounds were found to be of secondary importance.

Degradation of MTBE in dilute aqueous solution by gamma radiolysis

The radiolytic degradation of methyl tert-butyl ether (MTBE) in air-equilibrated dilute solution was investigated. Complete degradation of MTBE can be achieved within 5min of irradiation at 59.7Gy/min. The observed first-order degradation rate constant, called dose constant, increased from 0.04 to 0.56Gy−1 as the concentration of MTBE decreased from 92500 to 19μg/L. Tert-butyl formate, tert-butyl alcohol, acetone and methyl acetate were found to be the primary intermediates of the degradation reaction with yields of 47%, 11%, 6.4% and 9.1%, respectively. The degradation of MTBE or its intermediates was also found to depend on the concentrations of benzene and cupric ion. The study shows that the removal of MTBE can be significantly decreased with increasing concentration of benzene. Little affects were observed with the presence of cupric ions, while the degradation of TBF was apparently reduced. These results indicate that gamma radiolysis can be a potentially effective treatment for the removal of MTBE in contaminated water systems.

Impact of transverse and longitudinal dispersion on first-order degradation rate constant estimation

A two-dimensional analytical model is employed for estimating the first-order degradation rate constant of hydrophobic organic compounds (HOCs) in contaminated groundwater under steady-state conditions. The model may utilize all aqueous concentration data collected downgradient of a source area, but does not require that any data be collected along the plume centerline. Using a least squares fit of the model to aqueous concentrations measured in monitoring wells, degradation rate constants were estimated at a former manufactured gas plant (FMGP) site in the Midwest U.S. The estimated degradation rate constants are 0.0014, 0.0034, 0.0031, 0.0019, and 0.0053 day −1 for acenaphthene, naphthalene, benzene, ethylbenzene, and toluene, respectively. These estimated rate constants were as low as one-half those estimated with the one-dimensional (centerline) approach of Buscheck and Alcantar [Buscheck, T.E., Alcantar, C.M., 1995. Regression techniques and analytical solutions to demonstrate intrinsic bioremediation. In: Hinchee, R.E., Wilson, J.T., Downey, D.C. (Eds.), Intrinsic Bioremediation, Battelle Press, Columbus, OH, pp. 109–116] which does not account for transverse dispersivity. Varying the transverse and longitudinal dispersivity values over one order of magnitude for toluene data obtained from the FMGP site resulted in nearly a threefold variation in the estimated degradation rate constant—highlighting the importance of reliable estimates of the dispersion coefficients for obtaining reasonable estimates of the degradation rate constants. These results have significant implications for decision making and site management where overestimation of a degradation rate may result in remediation times and bioconversion factors that exceed expectations. For a complex source area or non-steady-state plume, a superposition of analytical models that incorporate longitudinal and transverse dispersion and time may be used at sites where the centerline method would not be applicable.

Bioremediation of diesel oil-contaminated soil by composting with biowaste

Soil spiked with diesel oil was mixed with biowaste (vegetable, fruit and garden waste) at a 1:10 ratio (fresh weight) and composted in a monitored composting bin system for 12 weeks. Pure biowaste was composted in parallel. In order to discern the temperature effect from the additional biowaste effect on diesel degradation, one recipient with contaminated soil was hold at room temperature, while another was kept at the actual composting temperature. Measurements of composting parameters together with enumerations and identifications of microorganisms demonstrate that the addition of the contaminated soil had a minor impact on the composting process. The first-order rate constant of diesel degradation in the biowaste mixture was four times higher than in the soil at room temperature, and 1.2 times higher than in the soil at composting temperature.

Use of pretreatment zones and zero-valent iron for the remediation of chloroalkenes in an oxic aquifer.

Pretreatment zones (PTZs) composed of sand, 10% zero-valent iron [Fe(0)]/sand, and 10% pyrite (FeS2)/sand were examined for their ability to prolong Fe(0) reactivity in above ground column reactors and a subsurface permeable reactive barrier (PRB). The test site had an acidic, oxic aquifer contaminated with tetrachloroethylene (PCE) and trichloroethylene (TCE). The 10% FeS2 and 10% Fe(0) PTZs removed dissolved oxygen and affected the pH and E(h) in the PTZ. None of the PTZs had any effect on pH or E(h) in the 100% Fe(0) zone. Nitrate and sulfate were removed more quickly in the Fe(0) zones preceded by either the 10% Fe(0) PTZ or 10% FeS2. PCE first-order degradation rate constants (k(obs)) decreased significantly (> 80%) with increasing column pore volumes regardless of the PTZ material used. k(obs) finally leveled off after approximately 1 yr of operation. The column results predict that the PRB will experience a breakthrough of PCE in 3-5 yr and illustrate the importance of incorporating temporal variations in degradation rate constants when designing PRBs.