Kinetics of transformation of 1,1,1-trichloroethane by Fe(II) in cement slurries

This study examines the applicability of the iron-based degradative solidification/stabilization (DS/S-Fe(II)) process to 1,1,1-trichloroethane (1,1,1-TCA), which is one of common chlorinated aliphatic hydrocarbons (CAHs) of concern at contaminated sites. DS/S-Fe(II) combines contaminant degradation by Fe(II) and immobilization by the hydration reactions of Portland cement. The transformation of 1,1,1-TCA by Fe(II) in 10% Portland cement slurries was studied using a batch slurry reactor system. The effects of Fe(II) dose, pH, and initial concentration of 1,1,1-TCA on the kinetics of 1,1,1-TCA degradation were evaluated. Degradation of 1,1,1-TCA in cement slurries including Fe(II) was very rapid and could be described by a pseudo-first-order rate law. The half-lives for 1,1,1-TCA were measured between 0.4 and 5h when Fe(II) dose ranged from 4.9 to 39.2mM. The pseudo-first-order rate constant increased with pH to a maximum near pH 12.5. A saturation rate equation was able to predict degradation kinetics over a wide range of target organic concentrations and at higher Fe(II) doses. The major transformation product of 1,1,1-TCA in mixtures of Fe(II) and cement was 1,1-dichloroethane (1,1-DCA), which indicates that degradation occurred by a hydrogenolysis pathway. A small amount of ethane was observed. The conversion of 1,1,1-TCA to ethane was better described by a parallel reaction model than by a consecutive reaction model.     

Pilot scale annular plug flow photoreactor by UV/H2O2 for the decolorization of azo dye wastewater

A pilot scale annular plug flow photoreactor with thin gap size, which combines with UV irradiation and hydrogen peroxide, was employed to deal with colored dyeing wastewater treatment. In the experiment, a mono-azo dye acid orange 10 was the target compound. The experimental parameters such as flow rate, hydrogen peroxide dosage, UV input power, pH and dye initial concentrations in a pilot scale photoreactor with flow rate of 9.32 m3day(-1) were investigated. Ultimately, the degradation rates were calculated and compared with a 100-l batch reactor. In our plug flow photoreactor design, the degradation rate of acid orange 10 was 233 times higher than that of 100-l annular batch reactor with same UV light source. The residence time needed for 99% decolorizing of 100 l of 20 mgl(-1) acid orange 10 wastewater was 26.9 min for the thin gap plug flow reactor and was far shorter than that of batch reactor needed.     

The effect of thermal explosion in a supercritical water

The conversion of hydrocarbons (eicosane, naphthalene, and synthetic bitumen) dissolved in super-critical water (SCW) was studied in a batch reactor at a pressure of P=30 MPa and a range of temperatures from 450 to 75°C. It was established that water participates in the conversion process on a chemical level: in particular, oxygen from water molecules is involved in the formation of carbon oxides. Even in the absence of added molecular oxygen, the process of naphthalene and bitumen conversion in a certain temperature interval exhibited an exothermal character. Upon adding O₂ into SCW, the oxidation reaction may proceed in a burning regime with self-heating of the mixture. Under certain conditions, the self-heating process may lead to the thermal explosion effect accompanied by ejection of the substance from the reactor, which is explained by the high rate of hydrocarbon burning in SCW.     

A titania thin film annular photocatalytic reactor for the degradation of polycyclic aromatic hydrocarbons in dilute water streams

An external lamp, annular photocatalytic reactor with titania immobilized on a quartz tube was used to degrade two polycyclic aromatic hydrocarbons (PAHs), viz. phenanthrene (PHE) and pyrene (PYR) from a dilute water stream. The thin film geometry was used to obtain both the mass transfer coefficients and intrinsic reaction rate constants for the two compounds on immobilized titania (Degussa P-25) particles. Beyond a feed velocity of 7 cmmin(-1), the conversion was solely reaction rate controlled and was not subjected to mass transfer limitations from the aqueous phase to the immobilized titania film. The overall reaction rate constant was independent of the feed concentration as large as the saturation aqueous solubility of the two compounds. However, the conversion was dependent on the ultraviolet (UV) light illumination intensity at the reactor. The quantum efficiency ranged from 3.7 x 10(-5) to 2.7 x 10(-4) which was somewhat low because of the very low aqueous concentrations of the chemicals. The overall reaction rate constant was 1.6 times larger for pyrene than for phenanthrene. Seven reaction intermediates were identified for the conversion of phenanthrene, while for the degradation of pyrene two intermediates were identified. The presence of the phthalate ester as an intermediate product in the degradation of both PAHs indicates the presence of a quinone in both cases which degrades to the products CO(2) and H(2)O, along with other stable intermediates. Mass balance in a batch reactor showed that only 28.6-40.1% of phenanthrene is mineralized to CO(2) in 1-3h of reaction although 35-67% of the parent compound has disappeared, confirming that a substantial fraction of the parent compound has been converted to stable intermediates that remain in the reactor. A plausible mechanism based on these observations is proposed.     

Destruction of carbon disulfide in aqueous solutions by sonochemical oxidation

Carbon disulfide (CS₂) is toxic to animals and aquatic organisms, and can also decompose to carbonyl sulfide (OCS) and hydrogen sulfide (H₂S) in aqueous environment. The kinetics of the sonochemical degradation of aqueous CS₂ was studied in a batch reactor at 20 kHz and 20 °C, and the effects of process parameters (e.g. concentration, ultrasonic intensity, irradiating gas) investigated. The concentrations of unbuffered CS₂ solutions used were (6.4–7.0)×10⁻⁴, 10.5×10⁻⁴ and (13.2–13.6)×10⁻⁴ M and the intensities were varied from 14 to 50 W. The reaction rate was found to be zero-order and the rate constant for the degradation at 20 °C and 14W in air was 21.1 μM/min using the largest initial concentration range studied. At the same initial concentration range but at 50 W (39.47 W/m²) the degradation rate of CS₂ was 46.7 μM/min, more than two times that at 14 W (11.04 W/m²). The rate of CS₂ sonochemical degradation in the presence of the different gases was in the order of He>air≥N₂O>Ar; the rate with helium was found to be about three times that of argon. The formation of sulfate (SO₄²⁻) as reaction product with air as the irradiating gas was enhanced in the presence of hydrogen peroxide (H₂O₂) and inhibited in the presence of 1-butanol. The sonochemical oxidation of CS₂ may prove to be an efficient and environmentally benign way for the removal of this hazardous pollutant from natural water and wastewater.     

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.     

Application of surfactant enhanced permanganate oxidation and bidegradation of trichloroethylene in groundwater

The industrial solvent trichloroethylene (TCE) is among the most ubiquitous chlorinated solvents found in groundwater contamination. The main objectives of this study were to evaluate the feasibility of using non-ionic surfactant Simple Green™ (SG) to enhance the oxidative dechlorination of TCE by potassium permanganate (KMnO₄) employing a continuous stir batch reactor system (CSBR) and column experiments. The effect of using surfactant SG to enhance the biodegradation of TCE via aerobic cometabolism was also examined. Results from CSBR experiments revealed that combination of KMnO₄ with surfactant SG significantly enhanced contaminant removal, particularly when the surfactant SG concentrated at its CMC. TCE degradation rates ranged from 74.1% to 85.7% without addition of surfactant SG while TCE degradation rates increased to ranging from 83.8% to 96.3% with presence of 0.1 wt% SG. Furthermore, results from column experiments showed that TCE was degraded from 38.1 μM to 6.2 μM in equivalent to 83.7% of TCE oxidation during first 560 min reaction. This study has also demonstrated that the addition of surfactant SG is a feasible method to enhance bioremediation efficiency for TCE contaminated groundwater. The complete TCE degradation was detected after 75 days of incubation with both 0.01 and 0.1 wt% of surfactant SG addition. Results revealed that surfactant enhanced chemical oxidation and bioremediation technology is one of feasible approaches to clean up TCE contaminated groundwater.     

Removal of trichloroethylene in reduced soil columns

A continuous soil column experiment was conducted to investigate reductive dechlorination of trichloroethylene (TCE) in soil system reductively manipulated by three types of reductants (Fe(II), dithionite, and Fe(II) + dithionite (combined treatment of Fe(II) and dithionite)). The soil column reduced by Fe(II) + dithionite has the greatest bed volumes (51.8) treated to breakthrough indicating that the combined treatment of Fe(II) and dithionite is more effective for the reductive dechlorination of TCE in the reduced soil column than the separate treatment of Fe(II) or dithionite. The measured bed volumes to breakthrough in control and treated soil columns were similar to the estimated bed volumes based on the result of batch kinetic experiment, differing by a factor of 0.96-1.02. The relative concentration of bromide (non-reactive tracer) reached the approximate value of 1 between 0.87 and 1.03 bed volume. C2 hydrocarbons (acetylene, ethylene, and ethane) were observed as transformation products in the effluents of soil columns treated by the reductants. However, no chlorinated intermediates were observed at the concentrations above detection limits throughout the experiment. Chloride was observed in the effluents of soil columns reduced by dithionite and Fe(II) + dithionite.     

Sequencing batch reactor performance treating PAH contaminated lagoon sediments

The applicability of sediment slurry sequencing batch reactors (SBR) to treat Venice lagoon sediments contaminated by polycyclic aromatic hydrocarbons (PAHs) was investigated, carrying out experimental tests. The slurry, obtained mixing tap water and contaminated sediments with 17.1 mg kg(-1) TS total PAHs content, was loaded to a 8l lab-scale completely stirred reactor, operated as a sequencing batch reactor. Oxygen uptake rate exerted by the slurry, measured by means of a DO-stat titrator, was used to monitor the in-reactor biological activity and to select the optimal operating conditions for the sediment slurry SBR. The PAHs removal efficiency was evaluated in different operating conditions, obtained changing the hydraulic retention time (HRT) of the lab-scale reactor and adding an external carbon source to the slurry. HRT values used during the experiments are 98, 70 and 35 days, whereas the carbon source was added in order to evaluate its effect on the biological activity. The results have shown a stable degradation of PAHs, with a removal efficiency close to 55%, not dependent on the addition of carbon source and the tested HRTs.     

Application of the electrosorption technique to remove Metribuzin pesticide

The present work deals with the removal of Metribuzin from aqueous solutions in a batch and continuous mode using electrosorption technique. This technique is based on the combination of two processes: the adsorption of Metribuzin into activated granular carbon (GAC) column and the application of the electrochemical potential. The effects of various experimental parameters (electrochemical potential, volumetric flow rate and initial Metribuzin concentration) on the removal efficiency were investigated. The pesticide sorption capacity at the breakthrough point of the GAC column reached 22 mg(pesticide)g(GAC)(-1). It was increased by more than 100% when the desired electrical potential (-50 mV/SCE) was applied in comparison with the conventional GAC column in similar experimental conditions without electrical potential. Evenmore, the electrosorption technique reduced considerably the drastic decrease encountered when passing from batch mode to continuous column mode.     

Bioremediation of anthracene contaminated soil in bio-slurry phase reactor operated in periodic discontinuous batch mode

Bioremediation of soil-bound anthracene was studied in a series of bio-slurry phase reactors operated in periodic discontinuous/sequencing batch mode under anoxic-aerobic-anoxic microenvironment using native soil microflora. Five reactors were operated for a total cycle period of 144 h (6 days) at soil loading rate of 16.66 kg soil/m(3)/day at 30 +/- 2 degrees C temperature. The performance of the bioreactors was studied at various substrate loading rates (volumetric substrate loading rate (SLR), 0.1, 0.2 and 0.3g anthracene/kg soil/day) with and without bioaugmentation (domestic sewage inoculum; 2 x 10(6) CFU/g of soil). Control reactor (without microflora) showed negligible degradation of anthracene due to the absence of biological activity. The performance of the bio-slurry system with respect to anthracene degradation was found to depend on both substrate loading rate and bioaugmentation. Application of bioaugmentation showed positive influence on the rate of degradation of anthracene. Anthracene degradation data was analysed using different kinetic models to understand the mechanism of bioremediation process in the bio-slurry phase system. Variation in pH/oxidation-reduction potential (ORP), soil microflora and oxygen consumption rate correlated well with the substrate degradation pattern observed during soil slurry phase anthracene degradation.     

Abatement of phenolic mixtures by catalytic wet oxidation enhanced by Fenton's pretreatment: effect of H2O2 dosage and temperature

Catalytic wet oxidation (CWO) of a phenolic mixture containing phenol, o-cresol and p-cresol (500mg/L on each pollutant) has been carried out using a commercial activated carbon (AC) as catalyst, placed in a continuous three-phase reactor. Total pressure was 16 bar and temperature was 127 degrees C. Pollutant conversion, mineralization, intermediate distribution, and toxicity were measured at the reactor outlet. Under these conditions no detoxification of the inlet effluent was found even at the highest catalyst weight (W) to liquid flow rate (Q(L)) ratio used. On the other hand, some Fenton Runs (FR) have been carried out in a batch way using the same phenolic aqueous mixture previously cited. The concentration of Fe(2+) was set to 10mg/L. The influence of the H(2)O(2) amount (between 10 and 100% of the stoichiometric dose) and temperature (30, 50, and 70 degrees C) on phenols conversion, mineralization, and detoxification have been analyzed. Phenols conversion was near unity at low hydrogen peroxide dosage but mineralization and detoxification achieved an asymptotic value at each temperature conditions. The integration of Fenton reagent as pretreatment of the CWO process remarkably improves the efficiency of the CWO reactor and allows to obtain detoxified effluents at mild temperature conditions and relatively low W/Q(L) values. For a given phenolic mixture a temperature range of 30-50 degrees C in the Fenton pretreatment with a H(2)O(2) dosage between 20 and 40% of the stoichiometric amount required can be proposed.     

Effectiveness of UV-based advanced oxidation processes for the remediation of hydrocarbon pollution in the groundwater: a laboratory investigation

The effectiveness of advanced oxidation processes in a batch and a flow reactor was investigated for the remediation of hydrocarbon pollution in the groundwater underlying a petrochemical industrial site. The main organic contaminants present in the groundwater were MTBE, benzene, alkyl-benzenes and alkyl-naphthalenes. Experimental results with a batch reactor showed that for all the organic contaminants the removal efficiency order is UV/TiO2 approximately UV/H2O2>UV (medium-pressure) in a synthetic aqueous solution, compared to UV/H2O2>UV (medium-pressure)>UV/TiO2 for the real polluted groundwater. The much lower performance of UV/TiO2 with respect to UV/H2O2 was inferred to the matrix of the groundwater, i.e. the salt content, as well as the organic and particulate matter. In fact, it is likely that the salts and dissolved organic matter quench the superoxide anion O2(-) and hydroxyl radicals just formed at the surface of the TiO2 catalyst. MTBE was the hardest compound to remove with each of the investigated treatments. UV and UV/TiO2 treatments were not able to reach a residual concentration of 10 microg/L (set by Italian legislation) even after 180 min. As for the UV/H2O2 process, only the MTBE degradation rate resulted affected by the initial H2O2 concentration, while for other compounds a complete removal was obtained within 20 min even with the lowest H2O2 concentration used (0.13 g/L). Only after 120 min of treatment, with an initial H2O2 concentration of 0.13 g/L, did the residual MTBE concentration fall below the above reported maximum admissible concentration. Instead, by using an initial concentration of 2g/L a residual concentration lower than 5 microg/L was obtained after just 30 min of reaction. The UV/H2O2 process was also investigated with a flow reactor. Results showed that it was more efficient than the batch reactor for removing MTBE, in terms of reaction time and initial H2O2 concentration required. This is consistent with the higher power of the UV lamp and with the different geometry of the flow reactor, which has a much shorter optical path than the batch reactor. By-product characterisation was also performed showing that t-butyl-formate and low molecular weight organic acids are formed as intermediate and final by-products, respectively. Finally, a preliminary evaluation of the operational cost of the UV/H2O2 process showed a value of 1.7 euro/m3 under the optimised condition.     

Reaction efficiencies and rate constants for the goethite-catalyzed Fenton-like reaction of NAPL-form aromatic hydrocarbons and chloroethylenes

The contaminants present as nonaqueous phase liquids (NAPLs) in the subsurface are long-term sources for groundwater pollution. Fenton-like reaction catalyzed by natural iron oxides such as goethite in soils is one of the feasible in situ chemical reactions used to remediate contaminated sites. This research evaluated the Fenton-like reaction of five chlorinated ethylenes and three aromatic hydrocarbons using goethite as the catalyst. The reaction efficiencies and rate constants of these compounds in NAPL and dissolved forms were compared. The content of goethite used in batch experiments was in the range similar to those found in subsurfaces. Low H2O2 concentrations (0.05 and 0.1%) were tested in order to represent the low oxidant concentration in the outer region of treatment zone. The results showed that at the tested goethite and H2O2 ranges, the majority of contaminants were removed in the first 120 s. When aromatics and chloroethylenes were present as NAPLs, their removal efficiencies and reaction constants decreased. The removal efficiencies of 0.02 mmol NAPL contaminants were 26-70% less than those of the dissolved. The measured rate constants were in the order of 10(9) M(-1) s(-1) for dissolved chlorinated ethylenes and aromatic hydrocarbons, but were 25-60% less for their NAPL forms. The initial dosage of H2O2 and NAPL surface areas (18.4-38.2 mm2) did not significantly affect reaction efficiencies and rate constants of chlorinated NAPLs. Instead, they were related to the octanol-water partition coefficient of compounds. For both dissolved and NAPL forms, aromatic hydrocarbons were more reactive than chlorinated ethylenes in Fenton-like reaction. These results indicated that the decrease in reaction efficiencies and rate constants of NAPL-form contaminants would pose more negative impacts on the less reactive compounds such as benzene and cis 1,2-DCE during goethite-catalyzed Fenton-like reaction.     

Heterogeneous photocatalytic degradation of p-toluenesulfonic acid using concentrated solar radiation in slurry photoreactor

In this work, the photocatalytic degradation (PCD) of p-toluenesulfonic acid (p-TSA) in batch reactor using concentrated solar radiation was investigated. The effect of the various operating parameters such as initial concentration of substrate, catalyst loading, solution pH and types of ions on photocatalytic degradation has been studied in a batch reactor to derive the optimum conditions. The rate of photocatalytic degradation was found to be maximum at the self pH (pH 3.34) of p-TSA. It was also observed that in the presence of anions and cations, the rate of PCD decreases drastically. The kinetics of photocatalytic degradation of p-TSA was studied. The PCD of p-TSA was also carried at these optimized conditions in a bench scale slurry bubble column reactor using concentrated solar radiation.     

Complete degradation of Orange G by electrolysis in sub-critical water

Complete degradation of azo dye Orange G was studied using a 500 mL continuous flow reactor made of SUS 316 stainless steel. In this system, a titanium reactor wall acted as a cathode and a titanium plate-type electrode was used as an anode in a subcritical reaction medium. This hydrothermal electrolysis process provides an environmentally friendly route that does not use any organic solvents or catalysts to remove organic pollutants from wastewater. Reactions were carried out from 30 to 90 min residence times at a pressure of 7 MPa, and at different temperatures of 180-250°C by applying various direct currents ranging from 0.5 to 1A. Removal of dye from the product solution and conversion of TOC increased with increasing current value. Moreover, the effect of salt addition on degradation of Orange G and TOC conversion was investigated, because in real textile wastewater, many salts are also included together with dye. Addition of Na(2)CO(3) resulted in a massive degradation of the dye itself and complete mineralization of TOC, while NaCl and Na(2)SO(4) obstructed the removal of Orange G. Greater than 99% of Orange G was successfully removed from the product solution with a 98% TOC conversion.     

Conversion of hydrocarbon fuel in elements of thermal protection of a hypersonic flight vehicle

The problems of increasing the cooling capacity of hydrocarbon fuel by its thermochemical transformation in elements of thermal protection of a hypersonic flight vehicle and hydrogen production on board for providing stable burning in a scramjet are considered. A comparison of the chemical reactions of cracking and steam conversion of hydrocarbons, as regards the cooling capacity and amount of hydrogen in reaction products, is made. The process of steam conversion of methane in a thermochemical reactor and the factors influencing the conversion level of hydrocarbons are studied experimentally.     

Cometabolic degradation of TCE in enriched nitrifying batch systems

The aim of this study was to evaluate the effect of the trace pollutant trichloroethylene (TCE) on the nitrification process and to assess its cometabolic degradation. Nitrification was accomplished in batch suspended growth systems containing an enriched nitrifier culture. The presence of TCE resulted in both the inhibition of specific oxygen uptake rate (SOUR) and specific ammonium utilization rate (qNH(4)-N). In both SOUR and qNH(4)-N a 50% decrease was observed in a TCE concentration range of 1000-2000 ppb. TCE was cometabolically degraded by this enriched nitrifier culture. The cometabolic degradation of TCE was found to be dependent on initial TCE concentration. The results may be applicable in the treatment of TCE containing industrial wastewaters and contaminated groundwaters and soils.