Reactivity of Fe(II)/cement systems in dechlorinating chlorinated ethylenes

Ferrous iron (Fe(II)) in combination with Portland cement is effective in reductively dechlorinating chlorinated organics and can be used to achieve immobilization and degradation of contaminants simultaneously. Reactivities of chlorinated ethylenes (perchloroethylene (PCE), trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), vinyl chloride (VC)) in Fe(II)/cement systems were characterized using batch slurry reactors. Reduction kinetics of the chlorinated ethylenes were sufficiently fast to be utilized for the proposed treatment scheme, and were described by a pseudo-first-order rate law. The order of reactivity of the chlorinated ethylenes was TCE>1,1-DCE>PCE>VC. Reduction of TCE and PCE mainly yielded acetylene, implying that the transformation of the two compounds occurred principally via reductive beta-elimination pathways. Transformation of 1,1-DCE and VC gave rise to primarily ethylene, implying that major degradation pathways were a reductive alpha-elimination for the former and a hydrogenolysis for the latter. The reactivity of the Fe(II)/cement systems in dechlorinating TCE was proportional to Fe(II) dose when the Fe(II)/cement mass ratio varied between 5.6 and 22.3%. The Fe(II)/cement systems with a higher Fe(II) loading were less extensively affected by pH in reductive reactions for TCE than in the previous experiments with PCE or chlorinated methanes. Amendment of Fe(II)/cement systems with Fe(III) addition was found effective in increasing the reactivity in the previous study, but the current findings indicated that the extent to which the reaction rate increased by the amendment might be dependent on the source of the cement and/or the compounds tested.     

Effects of transition metal and sulfide on the reductive dechlorination of carbon tetrachloride and 1,1,1-trichloroethane by FeS

Reductive dechlorination of carbon tetrachloride (CT) and 1,1,1-trichloroethane (1,1,1-TCA) by FeS with transition metals (Cu(II), Co(II), and Ni(II)) and hydrosulfide was characterized in this study. The batch kinetic experiments were conducted by spiking each stock solution of CT and 1,1,1-TCA into 33 g/L of FeS suspensions with and without transition metals at pH 7.5. No significant enhancement was observed in the reductive dechlorination of target compounds by FeS with 1mM transition metals. However, except the addition of Cu(II), the reduction rate of 1,1,1-TCA increased with increasing the concentration of transition metals. The rate constants with 10mM Co(II) and Ni(II) were 0.06 and 0.11h(-1), approximately 1.3 and 3.0 times greater than those by FeS alone. The addition of 20mM HS(-) also increased the rate constants of 1,1,1-TCA by FeS by one order of magnitude. SEM analysis showed that the addition of transition metal (Ni(II)) and HS(-) caused a noticeable morphologic change of FeS surface. The transition metal added was substituted by the structural iron resulting in the decrease of iron content of FeS (52.6-46.9%). One third of the transition metal in FeS suspension existed as zero-valent form playing a catalyst role to accelerate the reaction kinetics.     

Degradation of trichloroethylene and related compounds by <Emphasis Type="Italic">Mycobacterium</Emphasis> spp. isolated from soil

 Mycobacterium spp. strains TA5 and TA27 (ethane-utilizing bacteria), which can degrade trichloroethylene (TCE) and 1,1,1-trichloroethane (1,1,1-TCA), were isolated from soil. Both bacteria could cometabolically degrade dichloromethane, chloroform, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-TCA, 1,1,2-TCA, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, and TCE with ethane as a carbon source. They could not degrade carbon tetrachloride, freon 113, or tetrachloroethylene. The TCE degradation characteristics of strain TA27 were determined. Under a head-space gas containing 3% ethane, strain TA27 degraded more than 95% of TCE at an initial concentration of 1 mg l^–1 within 3 days. We observed good growth and TCE degradation between 25 and 35  °C. At an initial TCE concentration of 30 mg l^–1, it degraded 30% of TCE within 7 days. Although growth was inhibited for more than 50 mg l^–1 TCE at 3% ethane concentration, good growth and 50% degradation of TCE were observed at 12% ethane concentration within 14 days. High ethane concentration may mitigate the toxicity of TCE. Received: 24 January 2000 / Accepted: 10 March 2000     

CCT diagrams of tricalcium silicate: Part I. Influence of the Fe2O3 content

This work studies the effect of the iron oxide content on the kinetics of thermal decomposition of tricalcium silicate, or alite, the main component of Portland cement. The experiments allowed the construction of novel continuous cooling transformation (CCT) diagrams, showing the effect of the Fe content on the alite stability, under continuous cooling.     

Degradation of cyanobacteria toxin by advanced oxidation processes

Advanced oxidation processes (AOPs) using O(3), H(2)O(2), O(3)/H(2)O(2), O(3)/Fe(II), and Fenton treatment were investigated for the degradation of aqueous solutions of cyanobacteria. The effects of concentration of reactants, temperature, and pH on toxins degradation were monitored and the reaction kinetics was assessed. O(3) alone or combined with either H(2)O(2) or Fe(II) were efficient treatment for toxins elimination. A higher toxin oxidation tendency was observed with Fenton reaction; total toxins degradation (MC-LR and MC-RR) was achieved in only 60s. The ozonation treatment was successfully described by second-order kinetics model, with a first-order with respect to the concentration of either ozone or toxin. At 20 degrees C, with initial concentration of MC-LR of 1mg/L, the overall second-order reaction rate constant ranged from 6.79 x 10(4) to 3.49 x 10(3)M(-1)s(-1) as the solution pH increased from 2 to 11. The reaction kinetics of the other AOPs (O(3)/H(2)O(2), O(3)/Fe(II), and Fenton), were fitted to pseudo first-order kinetics. A rapid reaction was observed to took place at higher initial concentrations of O(3), H(2)O(2) and Fe(II), and higher temperatures. At pH 3, initial concentration of toxin of 1mg/L, the pseudo first-order rate constant, achieved by Fenton process, was in order of 8.76+/-0.7s(-1).     

Performance enhancement of batch aerobic digesters via addition of digested sludge

The impact of the feed sludge (FS) concentration and addition of digested sludge (DS) to an aerobic digester was evaluated with respect to its capability for removal of the total suspended solids (TSS) and volatile suspended solids (VSS). The aerobic digesters, which operated in a batch mode at constant temperature and mixing rate, were initially filled with FS to 25%, 50%, 75%, and 100% of the reactor's volume. The remaining volume of the reactor was occupied by the DS, having DS/FS ratio of 3, 1, 1/3, and 0. Analysis of the experimental data showed that in the absence of DS, TSS, and VSS destruction rates are very small; however, increasing DS/FS ratio from 1/3 to 3 results in 74-77% increase in VSS and TSS destruction, respectively. The increase of the DS/FS ratio associated with increased ratio of the measured viable biomass (Cc) to VSS concentration (Xv) suggested that DS serves as the source of viable cell mass needed for degradation of organic solids. Assuming pseudo-first-order kinetics, it was shown that while organic solid destruction rate constants (k) are inversely related to initial concentrations of sludge, their values increase with increasing DS/FS ratios.     

Photodegradation mechanism and kinetics of methyl orange catalyzed by Fe(III) and citric acid

In this study, the photodegradation process of methyl orange (MO) catalyzed by Fe(III) and citric acid and the reaction kinetics were investigated in detail at pHs from 2 to 8. The results show that the photodegradation of MO is slow in the presence of Fe(III) or citric acid alone. However, it is markedly enhanced when Fe(III) and citric acid coexist. High initial citric acid or initial Fe(III) concentrations lead to increased photodegradation of MO. And Fe(III) citrate mediated photodegradation of MO is optimized at pH 6. The photoproduction of hydroxyl radicals (·OH) in different catalytic systems was determined by HPLC. And the concentrations of Fe(II) and citric acid concentration in the process of the reaction were analyzed. The photodegradation of MO obeys to pseudo-zero order kinetics with respect to MO and the degradation reaction occurs in two phases. At the initial initiation stage, degradation rate is relatively slow, and significantly increases at a later acceleration stage.     

Degradation kinetics of fluorouracil-acetic-acid-dextran conjugate in aqueous solution

The degradation kinetics of fluorouracil-acetic-acid-dextran conjugate (FUAC-dextran) was investigated in various buffer solutions with different pH value and physiological saline solution at 60°C and 37°C, respectively. The hydrolytic reaction displayed pseudo-first-order degradation kinetics. Hydrolytic rate constant obtained was the function of pH value and independent of species of buffering agents. The smallest rate constant was observed at pH round 3.00. The activation energy of the hydrolytic reaction was estimated from Arrhenius equation as 88.73 ± 6.00 kJ·mol^-1. The special base catalytic degradation of the conjugate was observed from acidic to slight alkaline condition and the special base catalytic rate constants were calculated. The conjugate was more stable in physiological saline than that in buffer solution at pH 7.00 or 9.00 at 37°C. The results revealed that the conjugate was stable in acidic condition and will degrade in alkaline condition.     

Catalytic dechlorination of polychlorinated biphenyls in soil by palladium-iron bimetallic catalyst

Pd/Fe bimetallic particles were synthesized by chemical deposition and used to dechlorinate 2,2',4,5,5'-pentachlorobiphenyl in soil. Batch experiments demonstrated that the Pd/Fe bimetallic particles could effectively dechlorinate 2,2',4,5,5'-pentachlorobiphenyl. Dechlorination was affected by several factors such as reaction time, Pd loading, the amount of Pd/Fe used, initial soil pH, and 2,2',4,5,5'-pentachlorobiphenyl concentration. The results showed that higher Pd loading, higher dosage of Pd/Fe, lower initial concentration of 2,2',4,5,5'-pentachlorobiphenyl and slightly acid condition were beneficial to the catalytic dechlorination of 2,2',4,5,5'-pentachlorobiphenyl. The degradation of 2,2',4,5,5'-pentachlorobiphenyl, catalyzed by Pd/Fe followed pseudo-first-order kinetics.     

Degradation of trichloroethylene by Fenton reaction in pyrite suspension

Degradation of trichloroethylene (TCE) by Fenton reaction in pyrite suspension was investigated in a closed batch system under various experimental conditions. TCE was oxidatively degraded by OH in the pyrite Fenton system and its degradation kinetics was significantly enhanced by the catalysis of pyrite to form OH by decomposing H(2)O(2). In contrast to an ordinary classic Fenton reaction showing a second-order kinetics, the oxidative degradation of TCE by the pyrite Fenton reaction was properly fitted by a pseudo-first-order rate law. Degradation kinetics of TCE in the pyrite Fenton reaction was significantly influenced by concentrations of pyrite and H(2)O(2) and initial suspension pH. Kinetic rate constant of TCE increased proportionally (0.0030 ± 0.0001-0.1910 ± 0.0078 min(-1)) as the pyrite concentration increased 0.21-12.82 g/L. TCE removal was more than 97%, once H(2)O(2) addition exceeded 125 mM at initial pH 3. The kinetic rate constant also increased (0.0160 ± 0.005-0.0516 ± 0.0029 min(-1)) as H(2)O(2) concentration increased 21-251 mM, however its increase showed a saturation pattern. The kinetic rate constant decreased (0.0516 ± 0.0029-0.0079 ± 0.0021 min(-1)) as initial suspension pH increased 3-11. We did not observe any significant effect of TCE concentration on the degradation kinetics of TCE in the pyrite Fenton reaction as TCE concentration increased.     

Applicability of boron-doped diamond electrode to the degradation of chloride-mediated and chloride-free wastewaters

The degradation of diphenylamine (DPA) in aqueous solution by persulfate is investigated. Effects of pH, persulfate concentration, ionic strength, temperature and catalytic ions Fe(3+) and Ag(+) on the degradation efficiency of DPA by persulfate are examined in batch experiments. The degradation of DPA by persulfate is found to follow the pseudo-first-order kinetic model. Increasing the reaction temperature or persulfate concentration may significantly accelerate the DPA degradation. Fe(3+) and Ag(+) ions can enhance the degradation of DPA, and Ag(+) ion is more efficient than Fe(3+) ion. However, the increase of either the pH value or ionic strength will decrease the rate of DPA degradation. N-Phenyl-4-quinoneimine, N-carboxyl-4-quinoneimine, 4-quinoneimine and oxalic acid are identified as the major intermediates of DPA degradation, and a primary pathway for the degradation of DPA is proposed. The degradation of DPA in surface water, groundwater and seawater is also tested by persulfate, and more than 90% of DPA can be degraded at room temperature in 45min at an initial concentration of 20mgL(-1).     

Gallic acid degradation in aqueous solutions by UV/H2O2 treatment, Fenton's reagent and the photo-Fenton system

Gallic acid (3,4,5-trihydroxybenzoic acid) is a major pollutant present in the wastewater generated in the boiling cork process, as well as in other wastewaters from food manufacturing industries. Its decay in aqueous solutions has been studied by the action of several oxidation systems: monochromatic UV radiation alone and combined with hydrogen peroxide, Fenton's reagent and the combination Fenton's reagent with UV radiation (photo-Fenton system). The influence of the pH is discussed and the quantum yields are determined in the UV radiation system. Also, the influence of operating variables (initial concentrations of H2O2 and Fe(II), and pH) is established in the Fenton's reaction. The apparent pseudo-first-order rate constants are evaluated in all the experiments conducted in order to compare the efficiency of each one of the processes. Increases in the degradation levels of gallic acid are obtained in the combined processes in relation to the single UV radiation system, due to reactions of the very reactive OH*. These improvements are determined in every process by calculating the partial contribution to the overall decomposition rate of the radical pathways. For the oxidant concentrations applied, the most effective process in removing gallic acid was found to be the photo-Fenton system. The rate constant for the reaction of gallic acid with OH was also determined by means of a competition kinetics model, being its value 11.0+/-0.1 x 10(9)l mol(-1)s(-1).     

Degradation Kinetics of Fluorouracil-Acetic-Acid-Dextran Conjugate in Aqueous Solution

ABSTRACT

The degradation kinetics of fluorouracil-acetic-acid-dextran conjugate (FUAC-dextran) was investigated in various buffer solutions with different pH value and physiological saline solution at 60°C and 37°C, respectively. The hydrolytic reaction displayed pseudo-first-order degradation kinetics. Hydrolytic rate constant obtained was the function of pH value and independent of species of buffering agents. The smallest rate constant was observed at pH round 3.00. The activation energy of the hydrolytic reaction was estimated from Arrhenius equation as 88.73 ± 6.00 kJ·mol^?1. The special base catalytic degradation of the conjugate was observed from acidic to slight alkaline condition and the special base catalytic rate constants were calculated. The conjugate was more stable in physiological saline than that in buffer solution at pH 7.00 or 9.00 at 37°C. The results revealed that the conjugate was stable in acidic condition and will degrade in alkaline condition.     

Application of electrochemically generated ozone to the discoloration and degradation of solutions containing the dye Reactive Orange 122

Aqueous solutions containing the commercial azo dye Reactive Orange 122 (RO122) were ozonated in acid and alkaline conditions. Ozone was electrochemically generated using a laboratory-made electrochemical reactor and applied using semi-batch conditions and a column bubble reactor. A constant ozone application rate of 0.25gh(-1) was used throughout. Color removal and degradation efficiency were evaluated as function of ozonation time, pH and initial dye concentration by means of discoloration kinetics and COD-TOC removal. Experimental findings revealed that pH affects both discoloration kinetics and COD-TOC removal. A single pseudo-first-order kinetic rate constant, k(obs), for discoloration was found for ozonation carried out in alkaline solutions, contrary to acidic solutions where k(obs) depends on ozonation time. COD-TOC removal supports degradation of RO122 is more pronounced for alkaline conditions. Evaluation of the oxidation feasibility by means of the COD/TOC ratio indicates that the ozonation process in both acid and alkaline conditions leads to a reduction in recalcitrance of the soluble organic matter.     

Gas-liquid hybrid discharge-induced degradation of diuron in aqueous solution

Degradation of diuron in aqueous solution by gas-liquid hybrid discharge was investigated for the first time. The effect of output power intensity, pH value, Fe(2+) concentration, Cu(2+) concentration, initial conductivity and air flow rate on the degradation efficiency of diuron was examined. The results showed that the degradation efficiency of diuron increased with increasing output power intensity and increased with decreasing pH values. In the presence of Fe(2+), the degradation efficiency of diuron increased with increasing Fe(2+) concentration. The degradation efficiency of diuron was decreased during the first 4 min and increased during the last 10 min with adding of Cu(2+). Decreasing the initial conductivity and increasing the air flow rate were favorable for the degradation of diuron. Degradation of diuron by gas-liquid hybrid discharge fitted first-order kinetics. The pH value of the solution decreased during the reaction process. Total organic carbon removal rate increased in the presence of Fe(2+) or Cu(2+). The generated Cl(-1), NH(4)(+), NO(3)(-), oxalic acid, acetic acid and formic acid during the degradation process were also detected. Based on the detected Cl(-1) and other intermediates, a possible degradation pathway of diuron was proposed.     

Extraction solvent selection in environmental analysis.

A method for the prediction of a suitable solvent for the extraction of pesticides is outlined. The procedure is based on the Hildebrand solubility parameter, delta(t). The solubility parameter is broken down into three individual components, which are calculated by the addition of group contributions. To demonstrate the applicability of the approach pressurized fluid extraction was used to extract 4,4'-DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] and its metabolites, 4,4'-DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane] and 4,4'-DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene], from an historically contaminated soil from the United States and pentachlorophenol from a certified reference material (CRM524) using various solvents. Visual representation of the individual parameters predicted the ideal extraction solvent to be DCM for 4,4'-DDT and its metabolites and a mixture of acetonitrile and dichloromethane (1:1, v/v) for PCP. These findings were confirmed by the experimental results.     

Ultrasonic degradation of Rhodamine B in aqueous solution: influence of operational parameters

The aim of the study was to investigate decolorization of Rhodamine B (RB) in aqueous solution using ultrasonic degradation. The results showed that decolorization follows pseudo-first-order reaction kinetics. The apparent reaction rate constant (kap) was found to increase with decreasing pH and decreases with increasing initial RB concentration. Power density was very important parameter and increasing it causes a considerable increase of removal efficiency. UV-vis spectral changes of RB indicate that in the sonolysis of RB, the cleavage of aromatic chromophore ring structure and the N-deethylation take place, but decomposition of aromatic structure is predominant.     

The effect of substituent groups on the reductive degradation of azo dyes by zerovalent iron

To investigate the effects of substituent groups on the reductive degradation of azo dyes by zerovalent iron, Orange I, Orange II and Methyl Orange were selected as the model azo dyes with different substituent groups. The results showed that Orange I, Orange II and Methyl Orange could be effectively reduced by Fe(0), and the degradation of Orange I and Orange II could be described by the first-order kinetic model, while the degradation of Methyl Orange could be described by the zeroth-order kinetic model. The initial degradation rate followed the order as Orange I>Orange II>Methyl Orange under the same experimental conditions owing to the substituent effects. The degradation kinetic constants of Orange I and Orange II increased with the increase in the Fe(0) dosage, and with the decrease in the initial pH value and their initial concentration, while that of Methyl Orange increased with the decrease in the initial pH value, and with the increase in the Fe(0) dosage and their initial concentration. The results of high-performance liquid chromatography (HPLC)-mass spectra (MS) showed that sulfanilic acid was the same intermediate, while the second intermediate was 1-amino-4-naphthol for Orange I, 1-amino-2-naphthol for Orange II, and p-dimethylaminoaniline for Methyl Orange. It was suggested that the larger conjugated pi system of naphthalene rings of Orange I and Orange II for the delocalization of the nonbonding electron pairs of substituents and nitrogen in the azo bond might be favorable for the degradation of Orange I and Orange II, compared with the structure of Methyl Orange. The higher degradation rate of Orange I might be ascribed to its effective electron delocalization and favorable position effects, compared with Orange II. It should be concluded that the reductive degradation of azo dyes by zerovalent iron strongly depends on the effect of substituent groups.     

Investigation of Strontium (II) Sorption Kinetic and Thermodynamic onto Straw-derived Biochar

Biochars have attracted much research attention recently because of their potential applications in many environmental areas. In this study, rice straw-derived biochars produced at different pyrolysis temperatures (550–750°C) were used as adsorbents for the removal of strontium (II) under different experimental conditions of time, pH, and temperature. Sr(II) sorption equilibrium occurs after 30 min and its sorption maximum achieved at pH 6. The kinetic data obtained were analyzed to predict the constant rate of sorption using three common kinetic models: pseudo-first-order, pseudo-second-order equation, and intraparticle diffusion equation. The pseudo-second-order model was suitable for describing the sorption kinetics for the removal of Sr(II) from aqueous solution onto straw-derived biochar. Sorption of Sr(II) onto biochar was endothermic. Biochar has the highest Sr(II) sorption capacity in comparison to other adsorbents.