Mineralization Of Trichloroethylene Research Articles

Comparative studies of organic contaminant removal in different calcium sulfite-enhanced oxidant/Fe(II) systems: Kinetics, mechanisms, and differentiated degradation pathways

The application of S(IV) for the regeneration of Fe(II) has been widely investigated. As the common S(IV) sources, sodium sulfite (Na2SO3) and sodium bisulfite (NaHSO3) are soluble in the solution, resulting in excessive SO32− concentration and redundant radical scavenging problems. In this research, calcium sulfite (CaSO3) was applied as the substitution for the enhancement of different oxidant/Fe(II) systems. The advantages of CaSO3 could be summarized as follows: (1) it could sustainedly supplement SO32− for Fe(II) regeneration, preventing radical scavenging and unnecessary reagent waste; (2) the cost and toxicity of CaSO3 were extremely lower than that of other S(IV) sources; (3) the concentration of reactive species increased in the presence of CaSO3; and (4) after the reaction, SO42− would form CaSO4 precipitate, which would not increase the burden of SO42− in the solution. In the participation of CaSO3, the removal of trichloroethylene (TCE) and other organic contaminants were significantly promoted and different enhanced systems had high tolerance on complex solution conditions. The major reactive species in different systems were determined through qualitative and quantitative analyses. Eventually, the dechlorination and mineralization of TCE were measured and the differentiated degradation pathways in different CaSO3-enhanced oxidants/Fe(II) systems were elucidated.

Construction of mesoporous lanthanum orthovanadate/carbon nitride heterojunction photocatalyst for the mineralization of trichloroethylene

The search for stable, high-performance, and low-cost photocatalysts has received considerable interest. In this work, mesoporous LaVO4 nanoparticles were synthesized for the first time by applying the soft template, and g-C3N4 nanosheets were fabricated using a hard template to design mesoporous LaVO4/g-C3N4 heterostructures. The synthesized photocatalysts were assessed by the mineralization of trichloroethylene (TCE) in aqueous media during visible illumination. TEM and XRD measurements verified the existence of porous g-C3N4 with a high distribution of the monoclinic phase LaVO4 NPs (5 nm). The photocatalytic performance of the LaVO4/g-C3N4 heterojunction was much better than that of either LaVO4 or g-C3N4. 3%LaVO4/g-C3N4 exhibited the maximum photocatalytic ability, about 99% during a 3 h illumination at a degradation rate of 6.50 μmolL−1 min−1, which were ∼3.89- and ∼4.67-fold greater than parent LaVO4 and g-C3N4, respectively. The first-order kinetics calculations revealed that the 3% LaVO4/g-C3N4 heterostructure offered the highest rate constant of 0.0113 min−1, which estimated ∼8.7 and 4.9 folds larger than LaVO4 (0.0023 min−1) and g-C3N4 (0.0015 min−1), respectively. The importance of the LaVO4/g-C3N4 with superb photocatalytic efficiency was demonstrated based on the photoluminescence spectra, transient photocurrent curves, and UV–visible absorption spectra. The obtained LaVO4/g-C3N4 photocatalyst exhibited excellent regeneration and recyclability over five consecutive runs. The coupling of LaVO4 and g-C3N4 with matching alignment potentials and the synergetic effect were thought to be the most interesting processes to promote photocatalytic efficiency. The obtained LaVO4/g-C3N4 heterojunction possesses excellent photocatalytic efficiency and is a favorable candidate for potential applications in wastewater remediation using solar energy.

RuO2 nanoparticles-accommodated graphitic carbon nitride for significant enhancement in photocatalytic oxidation of trichloroethylene

It is greatly desired to construct bifunctional photocatalysts to achieve extremely effective photocatalytic ability. Herein, RuO2 nanoparticles (10 nm), accommodated in porous g-C3N4 to construct mesoporous RuO2/g-C3N4 heterojunctions, were prepared utilizing a modified sol-gel process in the existence of soft surfactant. The synthesized RuO2/g-C3N4 heterostructures were employed as photocatalysts in the mineralization of trichloroethylene (TCE) in an aqueous solution through visible light. The synthesized RuO2/g-C3N4 nanocomposites exhibited superior photocatalytic performance with 100% degradation of TCE within 150 min. The photodegradation rate of TCE of RuO2/g-C3N4 photocatalyst was remarkably promoted, compared with g-C3N4 and RuO2. The rate constant of 3%RuO2/g-C3N4 was determined to be 0.0127 min−1, which was 4.88 and 6.68 times higher than RuO2 (0.0026 min−1) and g-C3N4 (0.0019 min−1). This magnificent photocatalytic ability of RuO2/g-C3N4 nanocomposites can be interpreted to highly crystalline RuO2 NPs with small size, enhanced electron and mass transfer, visible light harvest and heterojunction structure with a synergistic effect. Furthermore, the synthesized photocatalyst could be recycled for five cycles with insignificant remarkable diminish in its photocatalytic ability. Fortunately, the photocatalytic ability of RuO2/g-C3N4 nanocomposites for TCE mineralization exhibited varied advances by utilizing visible light at room temperature without the employ of any oxidant.

Strategy for Modifying Layered Perovskites toward Efficient Solar Light-Driven Photocatalysts for Removal of Chlorinated Pollutants

We have explored an efficient strategy to enhance the overall photocatalytic performances of layered perovskites by increasing the density of hydroxyl group by protonation. The experimental procedure consisted of the slow replacement of interlayer Rb+ cation of RbLaTa2O7 Dion-Jacobson (DJ) perovskite by H+ via acid treatment. Two layered perovskites synthesized by mild (1200 °C for 18 h) and harsh (950 and 1200 °C, for 36 h) annealing treatment routes were used as starting materials. The successful intercalation of proton into D-J interlayer galleries was confirmed by FTIR spectroscopy, thermal analyses, ion chromatography and XPS results. In addition, the ion-exchange route was effective to enlarge the specific surface area, thus enhancing the supply of photocharges able to participate in redox processes involved in the degradation of organic pollutants. HLaTa_01 protonated layered perovskite is reported as a efficient photocatalyst for photomineralization of trichloroethylene (TCE) to Cl− and CO2 under simulated solar light. The enhanced activity is attributed to combined beneficial roles played by the increased specific surface area and high density of hydroxyl groups, leading to an efficiency of TCE mineralization of 68% moles after 5 h of irradiation.

Photocatalytic degradation of gaseous trichloroethylene on porous titanium dioxide pellets modified with copper(II) under visible light irradiation

Porous titanium dioxide pellets modified with copper(II) ion (Cu-TiO2) were synthesized by sol-gel method with dialysis for photocatalytic degradation of gaseous trichloroethylene (TCE) under visible light (VL) irradiation. TCE was completely degraded by passing the gas stream (mole fractions of oxygen and TCE were 0.2 and 1.75 × 10−4, respectively) at the flow rate of 25 mL min−1 through 0.2 g of the Cu-TiO2 pellets (Cu content: 0.1 atom%) calcined at 200 °C. TCE was converted mainly to carbon dioxide, dichloroacetic acid (DCAA), and inorganic chlorine species. Relatively small quantities of pentachloroethane (PCA) and trichloroacetaldehyde (TCAH) were detected as products on the Cu-TiO2 surface. Comparison with porous TiO2 pellets under ultraviolet irradiation revealed that more chlorinated products and less carbon dioxide were formed on Cu-TiO2 under VL irradiation. The mineralization of TCE to carbon dioxide was calculated to be only ca. 30.0%. It is noted that DCAA, PCA and TCAH were accumulated on the surface and were extracted with ethyl acetate. The porous Cu-TiO2 pellets show promise as the photocatalyst acting under VL irradiation for converting TCE gas to chlorinated compounds which can be used in industries.

Particularities of trichloroethylene photocatalytic degradation over crystalline RbLaTa2O7 nanowire bundles grown by solid-state synthesis route

This is the first report on synthesis and photocatalytic activity for trichloroethylene (TCE) degradation under simulated solar light over RbLaTa2O7 layered perovskites with predominant nanowire or platelet morphologies. SEM images witnessed that the one step thermal treatment at 1200 °C lead to formation of RbLaTa2O7 nanowires with diameter of 80–320 nm and several microns in length associated in bundles and sharp-edged, merged platelets (minor phase). The two-step annealing at 950 °C and 1200 °C resulted in decrease of wires bundle population and increase in that of platelets merged in facetted particles. The RbLaTa2O7 nanowires are made of by well-aligned atomic rows with preferred orientation toward the c-axis, relatively free of defect. High density of hydroxyl groups on the sample calcined in mild conditions (RbLaTa_01) favors the photo mineralization of TCE. In contrast, the activity of RbLaTa_02 annealed in harsh conditions (950 and 1200 °C), poor in surface hydroxyl groups, remained modest. The weak surface basicity directed the reaction mainly to generation of intermediate chlorinated compounds. Pd and Au were supported on RbLaTa2O7 perovskites as an alternative strategy to boost the removal of chlorinated pollutants by combining photocatalytic (mineralization) and catalytic (hydrodechlorination, HDC) processes. The mineralization of TCE to Cl− was drastically hindered in presence of methanol due to quenching of ⋅OH radicals by alcohol. The results suggested that the density of RbLaTa2O7 surface hydroxyl groups is essential for photo mineralization of TCE whereas the surface carbonate is beneficial for the formation of intermediate chlorinated product.

Enhancing surface corrosion of zero-valent aluminum (ZVAl) and electron transfer process for the degradation of trichloroethylene with the presence of persulfate

Though covered with a compact oxide film, unmodified zero-valent aluminum (ZVAl), showed a significant synergistic effect combined with persulfate (PS) for the degradation of trichloroethylene (TCE) over a wide initial pH range (3.00–10.00) without any induction period. In ZVAl/PS system, there are oxidizing species, including PS, O2, H2O and the target contaminant TCE, which will compete for electrons released from ZVAl corrosion. In order to really understand the reaction mechanism, in this work, the complicated surface corrosion and electron transfer processes for TCE degradation were deeply explored. Firstly, by the characterizations of SEM-EDS, TEM, size distribution, N2 adsorption–desorption isotherms, XRD and XPS, we found that pristine ZVAl was a core–shell structure and during the reaction the core was corroded and oxidized to Al-(hydr)oxide. After reaction, the oxide film was not directly removed, but became rougher, causing the increase of particle size, specific surface area, total pore volume and average pore size of ZVAl. The addition of PS can indeed activate ZVAl surface and accelerate ZVAl corrosion rate, and acidic environment is more conducive to the corrosion, which is opposite to the case without PS. Secondly, the dominant active species and electron transfer processes for TCE degradation were identified. SO4− was generated through electron transfer from ZVAl to PS directly. O2 may be involved in the process at acidic pH by forming O2− and H2O2. Hence, rather than the reductive removal by electron released from ZVAl, complete dechlorination and partial mineralization of TCE could be achieved, due to the high solubility and standard redox potential of PS which has more chance to capture electron and to the highly oxidative capacity of generated radicals.

Degradation of trichloroethylene in aqueous solution by rGO supported nZVI catalyst under several oxic environments

The reduced graphene oxide (rGO) supported nano zero-valent iron (nZVI) (nZVI-rGO) was synthesized successfully and applied in the several oxic environments to remove trichloroethylene (TCE). The nZVI-rGO had a better catalytic performance than bare nZVI for the TCE removal. Both aggregation of nZVI and agglomeration of rGO were in part prevented by loading the nZVI nanoparticles on the rGO sheet. Among all the oxic environments, the better removal of TCE was followed as the order of PMS > SPS > H2O2. Chemical scavenger tests were carried out to identify the reactive oxygen species (ROSs) generated in the removal of TCE, showing that in PMS and SPS systems, SO4− and HO were main radicals responsible for TCE removal, while HO and O2− were main radicals in H2O2 system. The possible mechanisms were proposed with nZVI-rGO under several oxic environments. The recyclability of nZVI-rGO, dechlorination and mineralization of TCE were investigated. These fundamental data confirmed the effectiveness of nZVI-rGO to remove TCE and could help selecting the suitable oxidants to use with nZVI-rGO in the actual field groundwater remediation.

Test of aerobic TCE degradation by willows (Salix viminalis) and willows inoculated with TCE-cometabolizing strains of Burkholderia cepacia.

Trichloroethylene (TCE) is a widespread soil and groundwater pollutant and clean-up is often problematic and expensive. Phytoremediation may be a cost-effective solution at some sites. This study investigates TCE degradation by willows (S. viminalis) and willows inoculated with three strains of B. cepacia (301C, PR1-31 and VM1330-pTOM), using chloride formation as an indicator of dehalogenation. Willows were grown in non-sterile, hydroponic conditions for 3weeks in chloride-free nutrient solution spiked with TCE. TCE was added weekly due to rapid loss by volatilization. Chloride and TCE in solution were measured every 2-3days and chloride and metabolite concentrations in plants were measured at test termination. Based on transpiration, no tree toxicity of TCE exposure was observed. However, trees grown in chloride-free solution showed severely inhibited transpiration. No or very little chloride was formed during the test, and levels of chloride in TCE-exposed trees were not elevated. Chloride concentrations in chloride containing TCE-free nutrient solution doubled within 23days, indicating active exclusion of chloride by root cell membranes. Only traces of TCE-metabolites were detected in plant tissue. We conclude that TCE is not, or to a limited extent (less than 3%), aerobically degraded by the willow trees. The three strains of B. cepacia did not enhance TCE mineralization. Future successful application of rhizo- and phytodegradation of TCE requires measures to be taken to improve the degradation rates.

Combination of non-thermal plasma and Pd/LaMnO3 for dilute trichloroethylene abatement

In this study, the oxidative abatement of dilute trichloroethylene (TCE) in humid air (RH=18%) was studied with combined use of a negative DC corona multi-pin-to-plate discharge and Pd/LaMnO3 catalyst downstream of the discharge. For this post-plasma catalytic (PPC) system the catalyst temperature was varied and the outcome on the TCE abatement and by-product distribution was investigated. The poor COx selectivity for the plasma system is attributed to the formation of unwanted polychlorinated by-products such as phosgene, dichloroacetylchloride (DCAC) and trichloroacetaldehyde (TCAD). At an energy density (ED) of 460J/L, the TCE abatement decreased as follows: PPC-150°C (96.2%)>PPC-200°C (91.7%)>PPC-100°C (89.1%)>NTP (82.3%). When the temperature of Pd/LaMnO3 was increased to 200°C the formation of DCAC was suppressed while the formation of phosgene was decreased in the order of 50% compared to the plasma alone system. For each PPC experiment, no ozone was detected in the outlet stream which proves that Pd/LaMnO3 is effective for ozone decomposition and substantially enhances the mineralization of TCE compared to the plasma alone system. Finally, XPS and ToF-SIMS studies have been performed after PPC experiments in order to investigate the possible surface modifications of the catalyst in the course of the reaction.

Trichloroethylene Degradation by Zero Valent Iron Activated Persulfate Oxidation

The present study describes the use of zero valent iron (Fe0 ) as a source for ferrous ion activated persulfate (PS) oxidation of trichloroethylene (TCE). The experimental results indicated that in the absence of TCE there was a lag time for persulfate decomposition when the reaction was activated by Fe0 . An initial pH drop in the Fe0 /PS system to acidic conditions was accompanied by the persulfate decomposition and a decrease in oxidation-reduction potential (ORP) values. Furthermore, in the TCE/Fe0 /PS system, the rapid TCE degradation was accompanied by the rapid persulfate decomposition and chloride ion formation as evidence of TCE mineralization. SEM images of Fe0 before and after persulfate oxidation exhibited significant corrosions of Fe0 . Acicular aggregate formation in the absence of TCE and coarse aggregate formation in the presence of TCE were observed. Moreover, the XRD spectrum revealed the formation of magnetite over the surface of Fe0 after contact with persulfate. Thus, Fe0 activated pe...

Reaction of Nonaqueous Phase TCE with Permanganate

Oxidative treatment of trichloroethylene (TCE) in the form of dense nonaqueous-phase liquid (DNAPL) by potassium permanganate (KMnO4) was investigated in a series of batch tests. The study focused on understanding the fundamental mechanisms of oxidative removal of DNAPL TCE by permanganate oxidation. Dissolution experiment for DNAPL TCE has been performed as a control experiment in the absence of KMnO4. DNAPL TCE dissolved into the aqueous phase until it reached the saturation concentration of 1200 mg/L (9.16 x 10(-3) M) at 20 degrees C. The rate of dissolution of DNAPL TCE was proportional to the volume of the DNAPL. In the presence of KMnO4, the experimental results showed that the amount of TCE oxidized during the reaction was increased continuously as [MnO4-] decreased even though the rate decreased as [MnO4-] decreased. It was apparent that more DNAPL TCE was removed with a faster rate for higher initial permanganate concentration. At high permanganate concentration, the aqueous concentration of TCE was kept low and practically constant by the chemical reaction between aqueous TCE and MnO4-. However, as MnO4- was consumed in the system, the aqueous concentration started to increase until it reached solubility. From experimental observation, 1.56-1.78 mol of MnO4- was consumed per mole of TCE oxidized. Furthermore, 2.85-2.98 mol of Cl- was released to the solution per mole of TCE oxidized. Since the complete mineralization of TCE requires 2.0 mol of MnO4- and releases 3 mol of Cl- per mol of TCE oxidized, the observed stoichiometric factors indicated incomplete mineralization of TCE, but nearly complete dechlorination. Enhancement factor due to chemical reaction was quantified experimentally. The enhancement factor was shown to be a function of the molar ratio of MnO4- to TCE in the system, and hence varied during the reaction period.

Photooxidation of aqueous trichloroethylene using a buoyant photocatalyst with reaction progress monitored via micro-headspace GC/MS

Although photooxidation has previously been shown to be successful in removing organic contaminants from water, methods combining the rapid photooxidation of the desired contaminant with easy catalyst manipulation and removal are few and far between. In the absence of an easy means of catalyst removal, the photooxidation process becomes more costly and time consuming, and photocatalysis cannot be employed as an in situ method for the remediation of aqueous organic contaminants. In this study, the photocatalyst was added to an aqueous trichloroethylene (TCE) solution in the form of TiO 2-coated buoyant microspheres. The solution, placed in a flow-cell photoreactor along with the buoyant catalyst, was irradiated with a UV-filtered Xenon light source. Limited sample sizes necessitated the development of a low-cost headspace GC/MS analysis method, utilizing a standard direct-injection autosampler. This analytical technique aptly monitored reaction progress and indicated that aqueous TCE concentration decreases by nearly 90% in the first hour of irradiation. Subsequent solvent extraction GC/MS analysis indicated that the TCE is initially sorbed by the photocatalyst spheres, but as irradiation continued, TCE is removed from the catalyst spheres surfaces. During the course of irradiation, the expected TCE mineralization product hydrochloric acid appeared, as indicated by a decrease in pH and ion chromatography analysis. The microsphere-born catalyst was easily removed from the treated solution by filtration. Thus, it is possible that a method for effective, low-cost in situ photooxidation of aqueous organic contaminants will be realized in the near future.

Degradation of trichloroethylene in a coupled anaerobic–aerobic bioreactor: Modeling and experiment

This work studied trichloroethylene (TCE) degradation in a single stage coupled anaerobic–aerobic granular biofilm reactor. The co-existence of aerobic methanotrophic and anaerobic methanogenic bacteria in this reactor was expected to allow for a combination of reductive and oxidative pathways of TCE degradation and result in mineralization of TCE. First, the anaerobic–aerobic coupling was simulated using a mathematical model. Simulations of TCE degradation under different operating conditions suggested the superiority of the coupled reactor system over either aerobic or anaerobic process alone. Next, the approach of combining aerobic–anaerobic TCE degradation was validated in a reactor experiment. The experiment confirmed degradation of TCE due to the co-existence of methanogenic and methanotrophic populations in a single reactor.

Microbial community structure and trichloroethylene degradation in groundwater

Trichloroethylene (TCE) is a prevalent contaminant of groundwater that can be cometabolically degraded by indigenous microbes. Groundwater contaminated with TCE from a US Department of Energy site in Ohio was used to characterize the site-specific impact of phenol on the indigenous bacterial community for use as a possible remedial strategy. Incubations of 14C-TCE-spiked groundwater amended with phenol showed increased TCE mineralization compared with unamended groundwater. Community structure was determined using DNA directly extracted from groundwater samples. This DNA was then analyzed by amplified ribosomal DNA restriction analysis. Unique restriction fragment length polymorphisms defined operational taxonomic units that were sequenced to determine phylogeny. DNA sequence data indicated that known TCE-degrading bacteria including relatives of Variovorax and Burkholderia were present in site water. Diversity of the amplified microbial rDNA clone library was lower in phenol-amended communities than in unamended groundwater (i.e., having Shannon-Weaver diversity indices of 2.0 and 2.2, respectively). Microbial activity was higher in phenol-amended ground water as determined by measuring the reduction of 2-(p-iodophenyl)-3(p-nitrophenyl)-5-phenyl tetrazolium chloride. Thus phenol amendments to groundwater correlated with increased TCE mineralization, a decrease in diversity of the amplified microbial rDNA clone library, and increased microbial activity.

Photocatalytic degradation of trichloroethylene in dry and humid atmospheres: role of gas-phase reactions

This study reports the role of the homogeneous photochemical oxidation (PCHO) reaction occurring in the gas-phase during heterogeneous photocatalytic degradation (PCTD) reaction of trichloroethylene (TCE) in humid and dry atmospheres. PCTD reaction was carried out in the presence of TiO2 glass fiber cloth (TiO2-GFC) while chlorine radicals generated from the exposure of chlorine gas to UV-illumination induced the PCHO reaction. The reaction profiles of the PCHO and PCTD reactions monitored independently in dry and humid atmospheres by in situ FTIR spectroscopy reveal the difference between the reaction pathways of phosgene formation and DCAC oxidation. Degradation of TCE to CO2 increased from 52% at 0% relative humidity (RH) to 71% at 100% RH during PCTD reactions while during PCHO reaction it decreased from 27% at 0% RH to 2% at 100% RH. Reactivity of both PCHO and PCTD reactions decreased with increasing RH. RH corresponding to ∼25% RH was found to be the most favorable condition for PCTD reactions because reasonably high reactivity and mineralization of TCE can be accomplished simultaneously.

Effects of aeration and organic loading rates on degradation of trichloroethylene in a methanogenic-methanotrophic coupled reactor

The effects of four aeration and four organic loading (OLR) rates on trichloroethylene (TCE) degradation in methanogenic-methanotrophic coupled reactors were studied using ethanol as the carbon source for the methanogens. Microcosm and PCR studies demonstrated that methanotrophs capable of mineralizing TCE and methanogens were present in the biomass throughout the study. The gene for the particulate form of methane monooxygenase (pMMO) was detected by PCR, but not that for the soluble form (sMMO). TCE mineralization by methanotrophs was therefore due primarily to pMMO activity. Low TCE concentrations were measured in effluent and off-gas samples in all cases. Volatilization losses were 0-5%. Dichloroethylene (DCE) was also observed, but vinyl chloride and ethylene were never detected. Changes in the aeration rate had no effect on TCE removal, but did influence DCE degradation. Reductive dechlorination of TCE to DCE was favored at low and no-aeration conditions, and DCE accumulation occurred due to slow DCE degradation. Low DCE levels were observed at the higher aeration rates, which indicated that conditions in these reactors were amenable to the aerobic co-metabolism of TCE and DCE. The OLR did have an effect on TCE removal. TCE and DCE removal were negatively affected when the OLR was increased. An OLR of 0.3 g COD l(rx)(-1)day(-1) or lower with an aeration rate of 3 l(O2 )l(rx)(-1)day(-1) and higher is the recommended operating condition of a coupled reactor for removal of TCE.

Gas-phase photocatalytic degradation of trichloroethylene on pretreated TiO2

This paper reports the effects of preillumination, prechlorination and prehydroxylation of TiO2 glass fiber cloth (TiO2-GFC) on the photocatalytic degradation (PCD) reaction of trichloroethylene (TCE) in gas–solid regime. The reaction was monitored in situ by FT-IR spectroscopy at room temperature (∼298K). Product analysis by gas chromatography–mass spectrometry (GC–MS) revealed the formation of a new by-product, 1,1-dichloroethane (1,1-DCE) in significant amount along with other known by-products. The photocatalytic activities of TiO2-GFC and the mineralization of TCE were dependent on preillumination, prehydroxylation and prechlorination while the product yield was significantly influenced by prehydroxylation and prechlorination of TiO2-GFC. Prechlorination increased the yields of phosgene (COCl2) and pentachloroethane (C2HCl5) while prehydroxylation decreased the yield of COCl2 with corresponding increases in the yield of oxalyl chloride (COClCOCl) and the mineralization of TCE, suggesting a possible surface-mediated hydrolysis of phosgene to COClCOCl in the latter case. Reaction schemes have been proposed to account for the formation of 1,1-DCE and COClCOCl. The photocatalytic activity of TiO2-GFC and the mineralization of TCE have been found to correlate with the concentration of HCl employed for the prechlorination of TiO2-GFC.

Aquifer Protist Response and the Potential for TCE Bioremediation with Burkholderia cepacia G4 PR1.

Bacterivorous protists have been recovered from pristine and contaminated aquifer environments, but the ecological role of these organisms in bioremediation strategies has not been well defined. Burkholderia cepacia G4 PR1 constitutively expresses a toluene ortho-monooxygenase (tom) due to a secondary transposition of a Tn5 transposable element in a trichloroethylene (TCE) degradative plasmid (TOM). Groundwater and sediment from a potential site for a TCE bioremediation field demonstration were used in laboratory microcosms to test the survival of this organism. In nonsterile aquifer sediment slurries, the bacterium was eliminated in a logrithmic decay concomitant with an increase in bacterivorous protists. A half-life for the organism calculated from extinction coefficients increased logarithmically with increasing inoculation density above 1 x 10(6) PR1 ml(-1). For inoculation densities below this level, the half-life of PR1 increased exponentially with decreasing inoculation density. The lowest half-lives corresponded to densities of bacteria that stimulate response of bacterivores. In a column system designed to incorporate aquifer flow, repeated addition of PR1 resulted in a buildup of bacterivore populations and reduced half-life of the bacterium. Addition of TCE and growth substrate in the eluent resulted in prolonged survival of PR1 and apparent mineralization of TCE. The results indicate significant but predictable losses due to native bacterivores would occur within and beyond a treatment zone where PR1 would be added to the aquifer, and mineralization of TCE in contaminated groundwater might be possible with repeated inoculation and addition of nutrients.

Mineralization of Trichloroethylene (TCE) by the White Rot Fungus Phanerochaete chrysosporium

Mineralization of Trichloroethylene (TCE) by the White Rot Fungus Phanerochaete chrysosporium