Feasibility of bioremediation of trichloroethylene contaminated sites by nitrifying bacteria through cometabolism with ammonia.

The autotrophic ammonia-oxidizing bacteria (Nitrosomonas sp.) are able to dechlorinate trichloroethylene (TCE) through cometabolism using ammonia (NH(3)) as a growth substrate. Cometabolic kinetics models suggest that TCE is a potent competitive inhibitor of NH(3) oxidation because it competes with NH(3) for oxidation by the enzyme of ammonia monooxygenase (AMO). In this study, an enriched culture of nitrifying bacteria was used to investigate the efficiencies of cometabolism of TCE by AMO. In addition, the relationships among specific growth substrate (NH(3)) utilization rate (qNH(3)), specific nongrowth substrate (TCE) cometabolic rate (qTCE), NH(3) and TCE concentrations, and NH(3)/TCE and TCE/NH(3) ratios were also analyzed. We found that the relationships between qNH(3) and NH(3) for the systems with and without TCE followed the Alvarez-Cohen competitive inhibition model and Monod model, respectively. Our results demonstrate that TCE could be cometabolized in a nitrification system when sufficient oxygen and NH(3)200 microg/l) were also found to show inhibitory effects towards NH(3) oxidation in enriched nitrifying culture. We also found that the NH(3)/TCE ratio rather than TCE concentrations alone exhibited strong correlation with qNH(3), much the same as the Ely activity recovery model presented. Our results suggest that the relationship between qTCE and TCE concentrations followed the Oldenhuis enzyme inactivation model for systems without NH(3).     

The effect of salinity conditions on kinetics of trichloroethylene biodegradation by toluene-oxidizing cultures

This study investigates the effect of salt (NaCl) conditions on the biodegradations of trichloroethylene (TCE) by mixed cultures enriched on toluene. Two cultures were separately cultivated in this investigation, involving culture LHTO4, cultivated with freshwater and culture HHTO4, cultivated with 3.5% (w/v) NaCl solution. Batch tests were conducted to elucidate the degradations of toluene, TCE and a mixture of toluene and TCE by cultures LHTO4 at salinities of 0, 2 and 3.5% and by HHTO4 at salinity of 3.5%. The measurements were analyzed with microbial kinetics. The results show that for culture LHTO4 in the resting cells, when the transient salinities increased from 0 to 3.5%, the maximum specific rate of TCE degradation, k(TCE), declined from 2.28 to 1.45 d(-1), and the observed TCE transformation capacity, T(c,obs), decreased from 0.060 to 0.036 mgTCE/mgVSS. In the presence of toluene, TCE degradation was more inhibited by toluene (inhibition coefficients, K(I,TOL) were 0.8, 2.2, and 0.96 mg/L for salinity 0, 2, and 3.5%, respectively) than toluene degradation was by TCE (K(I,TCE) were 14, 5.8, and 1000 mg/L for salinity 0, 2, and 3.5%, respectively). Under long-term salinity stress, the culture HHTO4 maintained its capacity to utilize toluene but lost its effectiveness in the cometabolic transformation of TCE: k(TCE) fell to 0.25 d(-1) and T(c,obs) dropped to 0.024 mgTCE/mgVSS. This work reveals that the degradation of TCE by toluene-oxidizing cultures under saline conditions can be best described by the chosen kinetic equations and experimentally estimated constants, which can thus be used to lay a foundation for the rational design of biological processes to remove TCE from saline solutions.     

Semicontinuous microcosm study of aerobic cometabolism of trichloroethylene using toluene

A semicontinuous slurry-microcosm method was applied to mimic trichloroethylene (TCE) cometabolic biodegradation field results at the Que-Jen in-situ pilot study. The microcosm study confirmed the process of aerobic cometabolism of TCE using toluene as the primary substrate. Based on the nucleotide sequence of 16S rRNA genes, the toluene-oxidizing bacteria in microcosms were identified, i.e. Ralstonia sp. P-10 and Pseudomonasputida. The first-order constant of TCE-degradation rate was 0.5 day(-1) for both Ralstonia sp. P-10 and P.putida. The TCE cometabolic-biodegradation efficiency measured from the slurry microcosms was 46%, which appeared pessimistic compared to over 90% observed from the in-situ pilot study. The difference in the TCE cometabolic-biodegradation efficiency was likely due to the reactor configurations and the effective time duration of toluene presence in laboratory microcosms (1 days) versus in-situ pilot study (3 days). The results of microcosm experiments using different toluene-injection schedules supported the hypothesis. With a given amount of toluene injection, it is recommended to maximize the effective time duration of toluene presence in reactor design for TCE cometabolic degradation.     

Degradation of phenol and TCE using suspended and chitosan-bead immobilized Pseudomonas putida

The degradability of phenol and trichloroethene (TCE) by Pseudomonas putida BCRC 14349 in both suspended culture and immobilized culture systems are investigated. Chitosan beads at a size of about 1-2mm were employed to encapsulate the P. putida cells, becoming an immobilized culture system. The phenol concentration was controlled at 100 mg/L, and that of TCE was studied from 0.2 to 20 mg/L. The pH, between 6.7 and 10, did not affect the degradation of either phenol or TCE in the suspended culture system. However, it was found to be an important factor in the immobilized culture system in which the only significant degradation was observed at pH >8. This may be linked to the surface properties of the chitosan beads and its influence on the activity of the bacteria. The transfer yield of TCE on a phenol basis was almost the same for the suspended and immobilized cultures (0.032 mg TCE/mg phenol), except that these yields occurred at different TCE concentrations. The transfer yield at a higher TCE concentration for the immobilized system suggested that the cells immobilized in carriers can be protected from harsh environmental conditions. For kinetic rate interpretation, the Monod equation was employed to describe the degradation rates of phenol, while the Haldane's equation was used for TCE degradation. Based on the kinetic parameters obtained from the two equations, the rate for the immobilized culture systems was only about 1/6 to that of the suspended culture system for phenol degradation, and was about 1/2 for TCE degradation. The slower kinetics observed for the immobilized culture systems was probably due to the slow diffusion of substrate molecules into the beads. However, compared with the suspended cultures, the immobilized cultures may tolerate a higher TCE concentration as much less inhibition was observed and the transfer yield occurred at a higher TCE concentration.     

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.     

Improving the performance of sequencing batch reactor (SBR) by the addition of zeolite powder

Two types of operation means "SBR reactor alone (control reactor)" and "adding zeolite powder into SBR reactor (test reactor)" were used to treat municipal wastewater. The test results revealed that zeolite powder addition could improve the activity of the activated sludge. It was investigated the specific oxygen utilization rate (SOUR) of the tested zeolite sludge were about double times that of the control activated sludge, and the nitrification rate and settling property of zeolite-activated sludge were both improved. Due to the combination of zeolite adsorption for NH(4)(+)-N and enhanced simultaneous nitrification and de-nitrification (SND), a higher nitrogen removal was observed in test reactor compared to the control reactor, and the addition of zeolite powder is helpful to inhabit sludge bulking. In addition, through long-term parallel shock load test, it was found that the zeolite powder addition could enhance the ability of activated sludge in resisting the shock load of organics and ammonium. Compared to the control activated sludge, zeolite powder added activated sludge could remove COD, NH(4)(+)-N, TN and TP significantly in a shorter cycle time. At the same operational time period, the test SBR could treat wastewater quantity 1.22 times that treated in control SBR.     

Effects of pH on dechlorination of trichloroethylene by zero-valent iron

The surface normalized reaction rate constants (k(sa)) of trichloroethylene (TCE) and zero-valent iron (ZVI) were quantified in batch reactors at pH values between 1.7 and 10. The k(sa) of TCE linearly decreased from 0.044 to 0.009l/hm(2) between pH 3.8 and 8.0, whereas the k(sa) at pH 1.7 was more than an order higher than that at pH 3.8. The degradation of TCE was not observed at pH values of 9 and 10. The k(sa) of iron corrosion linearly decreased from 0.092 to 0.018l/hm(2) between pH 4.9 and 9.8, whereas it is significantly higher at pH 1.7 and 3.8. The k(sa) of TCE was 30-300 times higher than those reported in literature. The difference can be attributed to the pH effects and precipitation of iron hydroxide. The k(sa) of TCE degradation and iron corrosion at a head space of 6 and 10ml were about twice of those at zero head space. The effect was attributed to the formation of hydrogen bubbles on ZVI, which hindered the transport the TCE between the solution and reaction sites on ZVI. The optimal TCE degradation rate was achieved at a pH of 4.9. This suggests that lowering solution pH might not expedite the degradation rate of TCE by ZVI as it also caused faster disappearance of ZVI, and hence decreased the ZVI surface concentration.     

Effects of n-hexadecane and PM-100 clay on trichloroethylene degradation by Burkholderia cepacia

Trichloroethylene (TCE) is a non-flammable, volatile organochlorine compound which was a widely used degreasing agent, anesthetic, and coolant prior to 1960, but has since been placed on the Environmental Protection Agency's (EPA) list of priority pollutants. The inadequate disposal practices for TCE have created numerous TCE-contaminated superfund sites. The most commonly employed practice for remediating TCE-contaminated sites is to purge the contaminant from the source and trap it onto an adsorbent which is disposed of in a landfill or by incineration. This investigation was undertaken to evaluate the effectiveness of Burkholderia cepacia strain G4 (G4) to regenerate used sorbents by degrading TCE from the sorbent directly or indirectly. The results of this investigation showed that G4 was capable of reducing TCE attached to PM-100 clay but at significantly reduced rate due to the slow desorption rate. Conversely, it was shown that G4 was capable of degrading TCE dissolved in n-hexadecane at the same rate as systems without n-hexadecane present. The reduction in TCE degradation when the TCE is attached to the PM-100 clay could be overcome by solvent rinsing the TCE from the clay with subsequent removal of the TCE from the n-hexadecane by G4.     

Effects of ferrous ions on the reductive dechlorination of trichloroethylene by zero-valent iron

The surface characteristics of zero-valent iron (ZVI) and the efficiency of reductive dechlorination of trichloroethylene (TCE) in the presence of ferrous ions were studied. The experimental results indicated that the acid-washing of a metallic iron sample enhanced the efficiency of TCE degradation by ZVI. This occurred because acid-washing changed the conformation of oxides on the surface of iron from maghemite (gamma-Fe(2)O(3)) to the more hydrated goethite (alpha-FeOOH), as was confirmed by XPS analysis. However, when ferrous ions were simultaneous with TCE in water, the TCE degradation rate decreased as the concentration of ferrous ion increased. This was due to the formation of passive precipitates of ferrous hydroxide, including maghemite and magnetite (Fe(3)O(4)), that coated on the surface of acid-washed ZVI, which as a result inhibited the electron transfer and catalytic hydrogenation mechanisms. On the other hand, in an Fe(0)-TCE system without the acid-washing pretreatment of ZVI, ferrous ions were adsorbed into the maghemite lattice which was then converted to semiconductive magnetite. Thus, the electrons were transferred from the iron surface and passed through the precipitates, allowing for the reductive dechlorination of TCE.     

Application of potassium permanganate as an oxidant for in situ oxidation of trichloroethylene-contaminated groundwater: a laboratory and kinetics study

The objectives of this bench-scale study were to (1) determine the optimal operational parameters and kinetics when potassium permanganate (KMnO4) was applied to in situ oxidize and remediate trichloroethylene (TCE)-contaminated groundwater and (2) evaluate the effects of manganese dioxide (MnO2) on the efficiency of TCE oxidation. The major controlling factors in the TCE oxidation experiments included molar ratios of KMnO4 to TCE (P value) and molar ratios of Na2HPO4 to Mn2+ (D value). Results show that the second-order decay model can be used to describe the oxidation when P value was less than 20, and the observed TCE decay rate was 0.8M(-1)s(-1). Results also reveal that (1) higher P value corresponded with higher TCE oxidation rate under the same initial TCE concentration condition and (2) higher TCE concentration corresponded with higher TCE oxidation rate under the same P value condition. Results reveal that significant MnO2 production and inhibition of TCE oxidation were not observed under acidic (pH 2.1) or slightly acidic conditions (pH 6.3). However, significant reduction of KMnO(4) to MnO2 would occur under alkaline condition (pH 12.5), and this caused the decrease in TCE oxidation rate. Results from the MnO2 production experiments show that MnO2 was produced from three major routes: (1) oxidation of TCE by KMnO4, (2) further oxidation of Mn2+, which was produced during the oxidation of TCE by KMnO4, and (3) reduction of MnO4(-1) to MnO2 under alkaline conditions. Up to 81.5% of MnO2 production can be effectively inhibited with the addition of Na2HPO4. Moreover, the addition of Na2HPO4 would not decrease the TCE oxidation rate.     

Photocatalysis of gaseous trichloroethylene (TCE) over TiO2: the effect of oxygen and relative humidity on the generation of dichloroacetyl chloride (DCAC) and phosgene

Batch photocatalytic degradation of 80+/-2.5 ppm V trichloroethylene (TCE) was conducted to investigate the effect of the oxygen and relative humidity (RH) on the formation of the dichloroacetyl chloride (DCAC) and phosgene. Based on the simultaneous ordinary differential equations (ODEs), the reaction rate constants of TCE ((2.31+/-0.28) approximately (9.41+/-0.63)x10(-2) min(-1)) are generally larger than that of DCAC ((0.94+/-1.25) approximately (9.35+/-1.71)x10(-3) min(-1)) by approximate one order. The phenomenon indicates the degradation potential of TCE is superior to that of DCAC. DCAC appreciably delivers the same degradation behavior with TCE that means there exists an optimum RH and oxygen concentration for photocatalysis of TCE and DCAC. At the time the peak yield of DCAC appears, the conversion ratio based on the carbon atom from TCE to DCAC is within the range of 30-83% suggesting that the DCAC generation is significantly attributed to TCE degradation. Regarding the phosgene formation, the increasing oxygen amount leads to the inhibitory effect on the phosgene yield which fall within the range of 5-15%. The formation mechanism of phosgene was also inferred that the Cl atoms attacking the C-C bond of DCAC results to the generation of phosgene rather than directly from the TCE destruction.     

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     

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.     

Enhanced dissolution of TCE in NAPL by TCE-degrading bacteria in wetland soils

The influence of trichloroethene (TCE) dechlorinating mixed cultures in dissolution of TCE in nonaqueous phase liquid (NAPL) via biodegradation was observed. Experiments were conducted in batch reactor system with and without marsh soils under 10 and 20 degrees C for 2 months. The dissolution phenomenon in biotic reactors containing mixed cultures was showed temporal increases compared to abiotic reactors treated with biocide. Effective NAPL-water transfer rate (K(m)) calculated in this study showed more than four times higher in biotic reactors than that in abiotic reactors. The results might be attributed to the biologically enhanced dissolution process via dechlorination in reactors. Temperature would be a factor to determine the dissolution rate by controlling bacterial activity. The TCE dechlorination occurred even in an interface of TCE-NAPL that demonstrated no previous TCE biodegradation, suggesting that microbes may be useful in developing source-zone bioremediation system. In conclusion, dechlorinating mixed culture could enhance dissolution in NAPL that may be useful in the application of source zone bioremediation.     

Synthesis and characterization of supported polysugar-stabilized palladium nanoparticle catalysts for enhanced hydrodechlorination of trichloroethylene

Palladium (Pd) nanoparticle catalysts were successfully synthesized within an aqueous phase using sodium carboxymethyl cellulose (CMC) as a capping ligand which offers a green alternative to conventional nanoparticle synthesis techniques. The CMC-stabilized Pd nanoparticles were subsequently dispersed within support materials using the incipient wetness impregnation technique for utilization in heterogeneous catalyst systems. The unsupported and supported (both calcined and uncalcined) Pd nanoparticle catalysts were characterized using transmission electron microscopy, energy dispersive x-ray spectrometry, x-ray diffraction, and Brunauer-Emmett-Teller surface area measurement and their catalytic activity toward the hydrodechlorination of trichloroethylene (TCE) in aqueous media was examined using homogeneous and heterogeneous catalyst systems, respectively. The unsupported Pd nanoparticles showed considerable activity toward the degradation of TCE, as demonstrated by the reaction kinetics. Although the supported Pd nanoparticle catalysts had a lower catalytic activity than the unsupported particles that were homogeneously dispersed in the aqueous solutions, the supported catalysts retained sufficient activity toward the degradation of TCE. In addition, the use of the hydrophilic Al(2)O(3) support material induced a mass transfer resistance to TCE that affected the initial hydrodechlorination rate. This paper demonstrates that supported Pd catalysts can be applied to the heterogeneous catalytic hydrodechlorination of TCE.     

Batch growth kinetics of an indigenous mixed microbial culture utilizing m-cresol as the sole carbon source

An indigenous mixed microbial culture, isolated from a sewage treatment plant located in Guwahati was used to study biodegradation of m-cresol in batch shake flasks. m-Cresol concentration in the growth media was varied from 100mg/L to 900mg/L. The degradation kinetics was found to follow a three-half-order model at all initial m-cresol concentrations with regression values greater than 0.97. A maximum observed specific degradation rate of 0.585h(-1) was observed at 200mg/L m-cresol concentration in the medium. In the range of m-cresol concentrations used in the study, specific growth rate of the culture and specific degradation rates were observed to follow substrate inhibition kinetics. These two rates were fitted to kinetic models of Edward, Haldane, Luong, Han-Levenspiel, and Yano-Koga that are used to explain substrate inhibition on growth of microbial culture. Out of these models Luong and Han-Levenspiel models fitted the experimental data best with lowest root mean square error values. Biokinetic constants estimated from these two models showed good potential of the indigenous mixed culture in degrading m-cresol in wastewaters.     

Bioremediation of endosulfan contaminated soil and water -- optimization of operating conditions in laboratory scale reactors

A mixed bacterial culture consisted of Staphylococcus sp., Bacillus circulans-I and -II has been enriched from contaminated soil collected from the vicinity of an endosulfan processing industry. The degradation of endosulfan by mixed bacterial culture was studied in aerobic and facultative anaerobic conditions via batch experiments with an initial endosulfan concentration of 50mg/L. After 3 weeks of incubation, mixed bacterial culture was able to degrade 71.58+/-0.2% and 75.88+/-0.2% of endosulfan in aerobic and facultative anaerobic conditions, respectively. The addition of external carbon (dextrose) increased the endosulfan degradation in both the conditions. The optimal dextrose concentration and inoculum size was estimated as 1g/L and 75mg/L, respectively. The pH of the system has significant effect on endosulfan degradation. The degradation of alpha endosulfan was more compared to beta endosulfan in all the experiments. Endosulfan biodegradation in soil was evaluated by miniature and bench scale soil reactors. The soils used for the biodegradation experiments were identified as clayey soil (CL, lean clay with sand), red soil (GM, silty gravel with sand), sandy soil (SM, silty sand with gravel) and composted soil (PT, peat) as per ASTM (American society for testing and materials) standards. Endosulfan degradation efficiency in miniature soil reactors were in the order of sandy soil followed by red soil, composted soil and clayey soil in both aerobic and anaerobic conditions. In bench scale soil reactors, endosulfan degradation was observed more in the bottom layers. After 4 weeks, maximum endosulfan degradation efficiency of 95.48+/-0.17% was observed in red soil reactor where as in composted soil-I (moisture 38+/-1%) and composted soil-II (moisture 45+/-1%) it was 96.03+/-0.23% and 94.84+/-0.19%, respectively. The high moisture content in compost soil reactor-II increased the endosulfan concentration in the leachate. Known intermediate metabolites of endosulfan were absent in all the above degradation studies.     

Waste green sands as reactive media for groundwater contaminated with trichloroethylene (TCE)

Waste green sands are byproducts of the gray iron foundry industry that consist of sand, binding agents, organic carbon, and residual iron particles. Because of their potential sorptive and reactive properties, tests were conducted to determine the feasibility of using waste green sands as a low cost reactive medium for groundwater treatment. Batch and column tests were conducted to determine the reactivity, sorptive characteristics, and transport parameters for trichloroethylene (TCE) solutions in contact with green sands. Normalized rate constants for TCE degradation in the presence of iron particles extracted from green sands were found to be comparable to those for Peerless iron, a common medium used to treat groundwater. Rate constants and partition coefficients obtained from the batch tests were found to be comparable to those from the column tests. Analytical modeling shows that reactive barriers containing green sand potentially can be used to treat contaminated groundwater containing TCE at typical concentrations observed in the field.     

The mechanism and applicability of in situ oxidation of trichloroethylene with Fenton's reagent

Fenton's reagent is the result of reaction between hydrogen peroxide (H(2)O(2)) and ferrous iron (Fe(2+)), producing the hydroxyl radical (-*OH). The hydroxyl radical is a strong oxidant capable of oxidizing various organic compounds. The mechanism of oxidizing trichloroethylene (TCE) in groundwater and soil slurries with Fenton's reagent and the feasibility of injecting Fenton's reagent into a sandy aquifer were examined with bench-scale soil column and batch experiment studies. Under batch experimental conditions and low pH values ( approximately 3), Fenton's reagent was able to oxidize 93-100% (by weight) of dissolved TCE in groundwater and 98-102% (by weight) of TCE in soil slurries. Hydrogen peroxide decomposed rapidly in the test soil medium in both batch and column experiments. Due to competition between H(2)O(2) and TCE for hydroxyl radicals in the aqueous solutions and soil slurries, the presence of TCE significantly decreased the degradation rate of H(2)O(2) and was preferentially degraded by hydroxyl radicals. In the batch experiments, Fenton's reagent was able to completely dechlorinate the aqueous-phase TCE with and without the presence of soil and no VOC intermediates or by-products were found in the oxidation process. In the soil column experiments, it was found that application of high concentrations of H(2)O(2) with addition of no Fe(2+) generated large quantities of gas in a short period of time, sparging about 70% of the dissolved TCE into the gaseous phase with little or no detectable oxidation taking place. Fenton's reagent completely oxidized the dissolved phase TCE in the soil column experiment when TCE and Fenton's regent were simultaneously fed into the column. The results of this study showed that the feasibility of injecting Fenton's reagent or H(2)O(2) as a Fenton-type oxidant into the subsurface is highly dependent on the soil oxidant demand (SOD), presence of sufficient quantities of ferrous iron in the application area, and the proximity of the injection area to the zone of high aqueous concentration of the target contaminant. Also, it was found that in situ application of H(2)O(2) could have a gas-sparging effect on the dissolved VOC in groundwater, requiring careful attention to the remedial system design.     

纳米材料TiO2光催化技术在空气净化中的应用

本文分析了纳米TiO2光催化处理室内VOC2的反应机理，以室内空气中常见的挥发性有机物为例，分析了单一初始浓度、室内湿度、紫外光强、迎面风速、温度等因素的影响，及其与反应速率的曲线关系，并与动力学模型L—H进行比较，趋势预测结果满意。