Mass removal of chlorinated ethenes from rough-walled fractures using permanganate

In situ chemical oxidation (ISCO) employing permanganate is an emerging technology that has been successful at enhancing mass removal from DNAPL source zones in unconsolidated media at the pilot-scale. The focus of this study was to evaluate the applicability of flushing a permanganate solution across two single vertical fractures in a laboratory environment to remove free phase DNAPL. The fracture experiments were designed to represent a portion of a larger fractured aquifer system impacted by a near-surface DNAPL spill over a shallow fractured rock aquifer. Each fracture was characterized by hydraulic and tracer tests, and the aperture field for one of the fractures was mapped using a co-ordinate measurement machine. Following DNAPL emplacement, a series of water and permanganate flushes were performed. To support observations from the fracture experiments, a set of batch experiments was conducted. The data from both fracture experiments showed that the post-oxidation effluent concentration was not impacted by the oxidant flush; however, changes in the aperture distribution, flow field, and flow rate were observed. These changes resulted in a significant decrease to the mass loading from the fractures, and were attributed to the build-up of oxidation by-products (manganese oxides and carbon dioxide) within the fracture which was corroborated by the batch experiment data and visual examination of the walls of one fracture. These results provide insight into the potential impact that a permanganate solution and oxidation by-products can have on the aperture distribution within a fracture and on DNAPL mass transfer rates. A permanganate flush or injection completed within a fractured rock aquifer may lead to the development of an insoluble product adjacent to the DNAPL which results in the reduction or complete elimination of advective regions near the DNAPL and reduces mass transfer rates. This outcome would have significant implications on the plume generating potential of the remaining DNAPL.     

Push-pull tests evaluating in situ aerobic cometabolism of ethylene, propylene, and cis-1,2-dichloroethylene

In situ aerobic cometabolic transformations of ethylene, propylene, and cis-1,2-dichloroethylene (c-DCE), by microorganisms stimulated on propane, were examined in groundwater contaminated with c-DCE and trichloroethylene (TCE). In situ measurements were performed by conducting field push-pull tests, which consisted of injecting site groundwater amended with a bromide tracer and combinations of propane, dissolved oxygen (DO), nitrate, ethylene, propylene, c-DCE, and TCE into existing monitoring wells and sampling the same wells over time. Mass balance and transformation rate calculations were performed after adjusting for dilution losses using measured tracer concentrations. Initial rates of propane utilization were very low; rates increased substantially following sequential additions of propane and DO. Evidence that propane and DO additions had stimulated organisms expressing a propane monoxygenase enzyme system and that had the capability to transform chlorinated aliphatic hydrocarbons (CAHs) included: (1) the transformation of injected ethylene and propylene to the cometabolic byproducts ethylene oxide and propylene oxide, (2) the transformation of c-DCE, and (3) the inhibition of these transformations in the presence of coinjected acetylene, a known monoxygenase mechanism-based inactivator. These results suggest that a series of push-pull tests performed with nontoxic chemical probes can be useful for detecting and monitoring in situ aerobic cometabolism of CAHs.     

Single-well, gas-sparging tests for evaluating the in situ aerobic cometabolism of cis-1,2-dichloroethene and trichloroethene

This study developed single-well, gas-sparging tests for assessing the feasibility of in situ aerobic cometabolism of trichloroethene (TCE) and cis-1,2-dichloroethene (cis-DCE) using propane and methane as growth substrates. Tests were performed in groundwater contaminated with TCE (100-400 microg l(-1)) and cis-DCE (20-60 microg l(-1)). A series of gas-sparging tests was performed by first sparging ("bubbling") gas mixtures in a well fitted with a "straddle" packer and then periodically sampling groundwater from the same well to develop concentration profiles and to estimate transformation rate coefficients. Evidence that gas-sparging of propane (or methane) and oxygen had stimulated organisms expressing a propane (or methane) monooxygenase enzyme system and the capability to transform TCE and cis-DCE included: (1) the transformation of sparged ethylene and propylene to their corresponding cometabolic by-products, ethylene oxide and propylene oxide, (2) the transformation of both cis-DCE and TCE in the propane-sparged well, (3) the transformation of cis-DCE in the methane-sparged well, and (4) the inhibition of ethylene and propylene transformations in the presence of acetylene, a known monooxygenase inactivator. At a well sparged with propane, first-order rate coefficients for propane utilization and ethylene and propylene transformation were similar, ranging from 0.007 to 0.010 h(-1). At the well sparged with methane, the propylene first-order transformation rate coefficient was 0.028 h(-1), a factor of 1.8 and 1.6 greater than methane and ethylene, respectively. The results demonstrated that gas-sparging tests are a rapid, low-cost means of assessing the potential for the in situ aerobic cometabolism of cis-DCE and TCE.     

Abiotic degradation of chlorinated ethanes and ethenes in water

INTRODUCTION: Chlorinated ethanes and ethenes are among the most frequently detected organic pollutants of water. Their physicochemical properties are such that they can contaminate aquifers for decades. In favourable conditions, they can undergo degradation. In anaerobic conditions, chlorinated solvents can undergo reductive dechlorination. DEGRADATION PATHWAYS: Abiotic dechlorination is usually slower than microbial but abiotic dechlorination is usually complete. In favourable conditions, abiotic reactions bring significant contribution to natural attenuation processes. Abiotic agents that may enhance the reductive dechlorination of chlorinated ethanes and ethenes are zero-valent metals, sulphide minerals or green rusts. OXIDATION: At some sites, permanganate and Fenton's reagent can be used as remediation tool for oxidation of chlorinated ethanes and ethenes. SUMMARY: Nanoscale iron or bimetallic particles, due to high efficiency in degradation of chlorinated ethanes and ethenes, have gained much interest. They allow for rapid degradation of chlorinated ethanes and ethenes in water phase, but they also give benefit of treating dense non-aqueous phase liquid.     

Identification and reliability of microbial aerobic respiration and denitrification kinetics using a single-well push-pull field test

Methods to derive reaction rates of microbial processes are important since these processes are determining many chemical reactions influencing groundwater quality. Thereby, it is not only important to derive the parameters, but also to have a firm idea about the reliability with which these are determined. Analysis of residuals, sensitivity analyses and analysis of joint confidence intervals provide an interesting tool for this purpose. The method is illustrated in this paper using a push-pull test designed to derive aerobic respiration and denitrification. Therefore, a test solution containing dissolved oxygen and nitrate as reactive tracer and bromide as non-reactive tracer was injected in organic matter rich sediment. Afterwards, this test solution was extracted and water quality was monitored. ReacTrans, a finite-difference, axial-symmetric groundwater flow and solute transport model was developed to simulate the test and derive hydraulic, solute transport and chemical parameters. Aerobic respiration and denitrification were simulated with Michaelis-Menten kinetics. Maximum reaction rates (10.4 and 2.4 mmol/ld for aerobic respiration and denitrification respectively) and Michaelis constants (0.14 and 0.1 mmol/l for aerobic respiration and denitrification respectively) were determined. The reliability with which these parameters are derived is indicated by analysis of residuals, sensitivities and joint confidence intervals. This shows that the Michaelis-Menten parameters can be derived reliable with a push-pull test, whereas the test is insensitive to effective porosity and hydraulic conductivity. Because of the small scale of the test, longitudinal dispersivity was very small and therefore unidentifiable.     

以萘为共代谢的芘的好氧生物降解

为更好有效去除地下水中的常见污染物芘,以萘为降解基质,利用苍白杆菌降解芘,并对反应影响因素进行了研究,模拟了反应动力学。结果表明：浓度为100 mg·L-1、pH=7、25℃、萘的初始反应24 h后萘的去除率达到99.84%,芘的去除率达到37.5%。另外,菌株在萘初始浓度不同的条件下对萘的降解符合一级动力学,对芘的降解符合二级动力学。结果表明苍白杆菌在去除地下水中的萘和芘方面具有很大前景。     

苯为共代谢基质的1,1-二氯乙烯的好氧生物降解研究

为了更好地去除地下水中常见的共同存在且难降解的有机物苯与1,1-二氯乙烯（DCE）,研究了从苯与DCE驯化的活性污泥中筛选获得的菌株DB-TS对苯与DCE的降解特性。当苯初始浓度相同时,随着DCE初始浓度的增加,苯的降解率不断减少;而DCE的去除率先增加后降低。苯的降解符合一级反应动力学;DCE的降解符合Monod动力...     

Numerical simulations of radon as an in situ partitioning tracer for quantifying NAPL contamination using push-pull tests

Presented here is a reanalysis of results previously presented by [Davis, B.M., Istok, J.D., Semprini, L., 2002. Push-pull partitioning tracer tests using radon-222 to quantify non-aqueous phase liquid contamination. J. Contam. Hydrol. 58, 129-146] of push-pull tests using radon as a naturally occurring partitioning tracer for evaluating NAPL contamination. In a push-pull test where radon-free water and bromide are injected, the presence of NAPL is manifested in greater dispersion of the radon breakthrough curve (BTC) relative to the bromide BTC during the extraction phase as a result of radon partitioning into the NAPL. Laboratory push-pull tests in a dense or DNAPL-contaminated physical aquifer model (PAM) indicated that the previously used modeling approach resulted in an overestimation of the DNAPL (trichloroethene) saturation (S(n)). The numerical simulations presented here investigated the influence of (1) initial radon concentrations, which vary as a function of S(n), and (2) heterogeneity in S(n) distribution within the radius of influence of the push-pull test. The simulations showed that these factors influence radon BTCs and resulting estimates of S(n). A revised method of interpreting radon BTCs is presented here, which takes into account initial radon concentrations and uses non-normalized radon BTCs. This revised method produces greater radon BTC sensitivity at small values of S(n) and was used to re-analyze the results from the PAM push-pull tests reported by Davis et al. The re-analysis resulted in a more accurate estimate of S(n) (1.8%) compared with the previously estimated value (7.4%). The revised method was then applied to results from a push-pull test conducted in a light or LNAPL-contaminated aquifer at a field site, resulting in a more accurate estimate of S(n) (4.1%) compared with a previously estimated value (13.6%). The revised method improves upon the efficacy of the radon push-pull test to estimate NAPL saturations. A limitation of the revised method is that 'background' radon concentrations from a non-contaminated well in the NAPL-contaminated aquifer are needed to accurately estimate NAPL saturation. The method has potential as a means of monitoring the progress of NAPL remediation.     

In situ assessment of microbial sulfate reduction in a petroleum-contaminated aquifer using push-pull tests and stable sulfur isotope analyses

Anaerobic microbial activities such as sulfate reduction are important for the degradation of petroleum hydrocarbons (PHC) in contaminated aquifers. The objective of this study was to evaluate the feasibility of single-well push-pull tests in combination with stable sulfur isotope analyses for the in situ quantification of microbial sulfate reduction. A series of push-pull tests was performed in an existing monitoring well of a PHC-contaminated aquifer in Studen (Switzerland). Sulfate transport behavior was evaluated in a first test. In three subsequent tests, we injected anoxic test solutions (up to 1000 l), which contained 0.5 mM bromide (Br-) as conservative tracer and 1 mM sulfate (SO4(2-)) as reactant. After an initial incubation period of 42.5 to 67.9 h, up to 1100 l of test solution/groundwater mixture was extracted in each test from the same location. During the extraction phases, we measured concentrations of relevant species including Br-, SO4(2-) and sulfide (S(-II)), as well as stable sulfur isotope ratios (delta 34S) of extracted, unconsumed SO4(2-) and extracted S(-II). Results indicated sulfate reduction activity in the vicinity of the test well. Computed first-order rate coefficients for sulfate reduction ranged from 0.043 +/- 0.013 to 0.130 +/- 0.015 day-1. Isotope enrichment factors (epsilon) computed from sulfur isotope fractionation of extracted, unconsumed SO4(2-) ranged from 20.2 +/- 5.5@1000 to 22.8 +/- 3.4@1000. Together with observed fractionation in extracted S(-II), isotope enrichment factors provided strong evidence for microbially mediated sulfate reduction. Thus, push-pull tests combined with stable sulfur isotope analyses proved useful for the in situ quantification of microbial sulfate reduction in a PHC-contaminated aquifer.     

Nitrate-consuming processes in a petroleum-contaminated aquifer quantified using push-pull tests combined with 15N isotope and acetylene-inhibition methods

Nitrate consumption in aquifers may result from several biogenic and abiotic processes such as denitrification, assimilatory NO3- reduction, dissimilatory NO3- reduction to ammonium (DNRA), or abiotic NO3- (or NO2-) reduction. The objectives of this study were to investigate the fate of NO3- in a petroleum-contaminated aquifer, and to assess the feasibility of using single-well push-pull tests (PPTs) in combination with 15N isotope and C2H2 inhibition methods for the quantification of processes contributing to NO3- consumption. Three consecutive PPTs were performed in a monitoring well of a heating oil-contaminated aquifer in Erlen, Switzerland. For each test, we injected 500 l of test solution containing 0.5 mM Br- as conservative tracer and either 0.5 mM unlabeled NO3- or approximately 0.3 mM 15N-labeled NO3- as reactant. Test solutions were sparged during preparation and injection with either N2, Ar or 10% C2H2 in Ar. After an initial incubation period of 1.5-3.2 h, we extracted the test solution/groundwater mixtures from the same location and measured concentrations of relevant species including Br-, NO3-, NO2-, N2O, N2, and NH4+. In addition, we determined the 15N contents of N2, N2O, NH4+, and suspended biomass from 15N/14N isotope-ratio measurements. Average total test duration was 50.5 h. First-order rate coefficients (k) were computed from measured NO3- consumption, N2-15N production and N2O-15N production. From measured NO3- consumption we obtained nearly identical estimates of k for all PPTs with small 95% confidence intervals, indicating good reproducibility and accuracy for the tests. Estimates of k from N2-15N production and N2O-15N production indicated that denitrification accounted for only 46-49% of observed NO3- consumption. Production of N2-15N in the presence of C2H2 was observed during one of the tests, which may be an indicator for abiotic NO3- reduction. Moreover, 15N isotope analyses confirmed occurrence of assimilatory NO3- reduction (0.58 at.% 15N in suspended biomass) and to a smaller extent DNRA (up to 4 at.% 15N in NH4+). Our results indicated that the combination of PPTs, 15N-isotope and C2H2 inhibition methods provided improved information on denitrification as well as alternative fates of NO3- in this aquifer.     

Assessment of the natural attenuation of chlorinated ethenes in an anaerobic contaminated aquifer in the Bitterfeld/Wolfen area using stable isotope techniques, microcosm studies and molecular biomarkers

The in situ degradation of chlorinated ethenes was assessed in an anaerobic aquifer using stable isotope fractionation approaches, microcosm studies and taxon specific detection of specific dehalogenating groups of bacteria. The aquifer in the Bitterfeld/Wolfen region in Germany contained all chlorinated ethenes, benzene and toluene as contaminants. The concentrations and isotope composition of the chlorinated ethenes indicated biodegradation of the contaminants. Microcosm studies confirmed the presence of in situ microbial communities capable of the complete dechlorination of tetrachloroethene. Taxon specific investigation of the microbial communities indicated the presence of various potential dechlorinating organisms including Dehalococcoides, Desulfuromonas, Desulfitobacterium and Dehalobacter. The integrated approach, using metabolite spectra, molecular marker analysis and isotope studies, provided several lines of evidence for natural attenuation of the chlorinated ethenes.     

好氧微生物降解林丹过程中碳-氯二维稳定同位素的分馏特性

六氯环己烷 (HCH) 是一种持久性污染物,环境存量较大时会造成污染,定量研究其在环境中的迁移转化过程具有重要意义。研究了3种好氧微生物Sphingobium quisquiliarum P25、Sphingobium ummariense RL-3和Sphingobium sp. F2降解γ-HCH (林丹) 的过程,应用单体稳定同位素分析技术 (CSIA) 探究了不同微生物对HCH的降解效果,及其对HCH转化与迁移行为的影响。结果表明：1) 3种微生物降解γ-HCH的过程符合一级反应动力学原理;2) 降解过程中碳分馏系数 (ε_C) 分别为−(4.3±0.4)‰,−(1.6±0.1) ‰和−(5.7±0.5) ‰,氯同位素分馏系数 (ε_Cl) 分别为−(1.1±0.6) ‰,−(1.5±0.2) ‰和−(1.5±0.4)‰;3) 二维同位素分馏系数 (Λ_C-Cl) 分别为(3.0±0.3),(1.1±0.1)和(2.7±0.2)。本研究结果可为应用单体稳定同位素分析技术解析复杂环境中HCH的迁移转化过程并评估HCH污染场地修复效果提供参考。     

Comparison of an assay for Dehalococcoides DNA and a microcosm study in predicting reductive dechlorination of chlorinated ethenes in the field

The study aims to compare the detection of 16S rRNA gene of Dehalococcoides species and the microcosm study for biotransformation in predicting reductive dechlorination of chlorinated ethenes in ground water at hazardous waste sites. A total of 72 ground water samples were collected from 12 PCE or TCE contaminated sites in the United States. The samples were analyzed and used to construct microcosms in the laboratory. The results showed that the presence of Dehalococcoides DNA was well associated with dechlorination to ethene in the field. Nearly half of the wells where Dehalococcoides DNA was detected had ethene as a dechlorination end product. In comparison, for ground water samples of 16 wells where ethene was detected, ethene was produced in 11 of the corresponding microcosms. For most microcosms, during two years of incubation, dechlorination was less extensive than that observed in the field.     

An integrated anaerobic/aerobic bioprocess for the remediation of chlorinated phenol-contaminated soil and groundwater.

An investigation of biodegradation of chlorinated phenol in an anaerobic/aerobic bioprocess environment was made. The reactor configuration used consisted of linked anaerobic and aerobic reactors, which served as a model for a proposed bioremediation strategy. The proposed strategy was studied in two reactors before linkage. In the anaerobic compartment, the transformation of the model contaminant, 2,4,6-trichlorophenol (2,4,6-TCP), to lesser-chlorinated metabolites was shown to occur during reductive dechlorination under sulfate-reducing conditions. The consortium was also shown to desorb and mobilize 2,4,6-TCP in soils. This was followed, in the aerobic compartment, by biodegradation of the pollutant and metabolites, 2,4-dichlorophenol, 4-chlorophenol, and phenol, by immobilized white-rot fungi. The integrated process achieved elimination of the compound by more than 99% through fungal degradation of metabolites produced in the dechlorination stage. pH correction to the anaerobic reactor was found to be necessary because acidic effluent from the fungal reactor inhibited sulfate reduction and dechlorination.     

Determination of the aerobic biodegradability of polymeric material in aquatic batch tests

Results of an international ring-test of two laboratory methods are presented for investigating the biodegradability of organic polymeric test materials in aquatic test systems based on respirometry and the evolution of carbon dioxide. These methods are developed further from the well-known standardized biodegradation tests ISO 9408 (1999) and ISO 9439 (1999), which have been successfully used for many years. The most important improvements are the extension of the test period up to six months, the increase of the buffer capacity and nutrient supply of the inorganic medium, an optimization of the inoculation, and optionally, the possibility of a carbon balance. A ring test, organized by the International Biodeterioration Research Group (IBRG), was run using a poly(,-caprolactone)-starch blend and an aliphatic-aromatic co-polyester as test materials and a microcrystalline cellulose powder as a reference material. The test results and the experience gained by the participants showed that the methods are suitable and practicable. The test methods have been meanwhile established as standards ISO 14851 (1999) and ISO 14852 (1999).     

Assessing the transformation of chlorinated ethenes in aquifers with limited potential for natural attenuation: added values of compound-specific carbon isotope analysis and groundwater dating

The evaluation of biotransformation of chlorinated ethenes (CEs) in contaminated aquifers is challenging when variable redox conditions and groundwater flow regime are limiting factors. By using compound-specific stable carbon isotope analysis (C-CSIA) and ³H-³He based groundwater dating, we assessed three CE-contaminated field sites that differed in groundwater flow velocities, redox conditions, and level of contamination. CE isotopic signatures and carbon isotopic mass balances were applied to quantify CE transformation, whereas groundwater dating allowed determining degradation timescales and assessing hydrodynamic regimes. The combination of these techniques enabled at all field sites to indicate zones within the aquifers where CE dechlorination preferably occurred, sometimes even to metabolites of no toxic concern. However, the natural transformation processes were insufficient to mitigate the entire CE contamination at the studied sites. Such situations of limited transformation are worldwide far more common than sites where optimal natural (mainly redox) conditions are enabling complete CEs degradation. Despite such constraints for natural transformation, this study showed that even under non-favorable biogeochemical CEs degradation, the combination of CSIA and groundwater dating provide valuable information to the understanding of the fate of the CEs, thus, being an important contribution in the definition of efficient remediation measures at any given biogeochemical conditions.     

Evaluation of the mortality experience of workers exposed to the chlorinated dioxins

Mortality patterns were analyzed for the time period 1940 through 1979 of 2,189 men with potential occupational exposure to chlorinated dibenzo-p-dioxins. Special attention was directed toward 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and deaths due to soft-tissue sarcoma, non-Hodgkins lymphoma, Hodgkins disease, liver cancer, stomach cancer, and nasal or nasopharyngeal cancer. With United States white males as the comparison population for this employee cohort, the stadardized mortality ratio for all causes of death was 91 and for total malignant neoplasms, 96. Among the malignancy categories of particular interest, none demonstrated a significant deviation from expected. Nor were any significant trends noted for any specific cause of death category when analyzed by estimated cumulative exposure.     

Use of tracer tests to evaluate the impact of enhanced-solubilization flushing on in-situ biodegradation

Tracer tests were conducted to evaluate the effect of a complexing sugar flush (CSF) on in-situ biodegradation potential at a site contaminated by jet fuel, solvents, and other organic compounds. Technical-grade hydroxypropyl-beta-cyclodextrin was used during the CSF study, which was conducted in a hydraulically isolated cell emplaced in a surficial aquifer. In-situ biodegradation potential was assessed with the use of tracer tests, which were conducted prior to and immediately following the CSF study. Ethanol, hexanol, and benzoate were used as the biodegradable tracers, while bromide was used as a nonreactive tracer. The results indicate that the biodegradation of benzoate was similar for both tracer tests. Conversely, the biodegradation of ethanol (23% increase) and hexanol (41% increase) was greater for the post-CSF tracer test. In addition, analysis of core samples collected from within the test cell indicates that the population density of aerobic jet-fuel degraders increased in the vicinity of the injection wells during the CSF. These results indicate that the cyclodextrin flush did not deleteriously affect the indigenous microbial community. This study illustrates that tracer tests can be used to evaluate the impact of remediation activities on in-situ biodegradation potential.