Time Varying Optimization for Monitoring Multiple Contaminants under Uncertain Hydrogeology

This study presents a method for identifying cost effective sampling designs for long-term monitoring of remediation of groundwater over multiple monitoring periods under uncertain flow conditions. A contaminant transport model is used to simulate plume migration under many equally likely stochastic hydraulic conductivity fields and provides representative samples of contaminant concentrations. Monitoring costs are minimized under a constraint to meet an acceptable level of error in the estimation of total mass for multiple contaminants simultaneously over many equiprobable realizations of hydraulic conductivity field. A new myopic heuristic algorithm (MS-ER) that combines a new error-reducing search neighborhood is developed to solve the optimization problem. A simulated annealing algorithm using the error-reducing neighborhood (SA-ER) and a genetic algorithm (GA) are also considered for solving the optimization problem. The method is applied to a hypothetical aquifer where enhanced anaerobic bioremediation of four toxic chlorinated ethene species is modeled using a complex contaminant transport model. The MS-ER algorithm consistently performed better in multiple trials of each algorithm when compared to SA-ER and GA. The best design of MS-ER algorithm produced a savings of nearly 25% in project cost over a conservative sampling plan that uses all possible locations and samples.     

Field Note: Phytoremediation of Chlorinated Ethenes in Seepline Sediments: Tree Selection

Phytoremediation of chlorinated ethene (CE)-contaminated water was investigated at the Savannah River Site in Aiken, SC, USA. Perchloroethylene (PCE) and trichloroethylene (TCE) are present where CE-contaminated groundwater currently outcrops in seepline soils. Results of constructed and planted test cells, filled with soil from a noncontaminated seepline area and supplied with CE-contaminated groundwater (48 ppb) in the field for one season are presented. These test cells were planted with loblolly pines, hybrid poplars, coyote willow, and sweet gum. Cis-dichloroethylene (cDCE), a byproduct from rhizosphere microbial activity, was detected in the soils as well as some tree tissues. All trees tested were found to uptake both PCE and TCE (5–50 pbb/gm dry wt).     

Enhanced dechlorination of chloroethenes by granular sludge under microaerophilic conditions

This study investigates an innovative dechlorination process using anaerobic granular sludge that was partially exposed to oxygen. The exposure supported a synchronously anaerobic and aerobic bioconversion process that combined reductive dechlorination with aerobic co-oxidation in a sludge granule. Experimental results showed that the highest dechlorination rates of tetrachloroethene, trichloroethene, cis-dichloroethene and vinyl chloride were 6.44, 2.98, 1.70 and 0.97 nmol/gVS day, at initial O₂ concentrations of 10, 100, 5 and 0%, respectively. Strictly anaerobic conditions favored the dechlorination of vinyl chloride while absolutely aerobic conditions were preferred for trichloroethene dechlorination. Microaerophilic conditions are suggested to ensure the overall biodegradation of the chlorinated ethenes present in groundwater as a mixture.     

The role of microbial reductive dechlorination of TCE at a phytoremediation site

In April 1996, a phytoremediation field demonstration site at the Naval Air Station, Fort Worth, Texas, was developed to remediate shallow oxic ground water (< 3.7 m deep) contaminated with chlorinated ethenes. Microbial populations were sampled in February and June 1998. The populations under the newly planted cottonwood trees had not yet matured to an anaerobic community that could dechlorinate trichloroethene (TCE) to cis-1,2-dichloroethene (DCE); however, the microbial population under a mature (approximately 22-year-old) cottonwood tree about 30 m southwest of the plantings had a mature anaerobic population capable of dechlorinating TCE to DCE, and DCE to vinyl chloride (VC). Oxygen-free sediment incubations with contaminated groundwater also demonstrated that resident microorganisms were capable of the dechlorination of TCE to DCE. This suggests that a sufficient amount of organic material is present for microbial dechlorination in aquifer microniches where dissolved O2 concentrations are low. Phenol, benzoic acid, acetic acid, and a cyclic hydrocarbon, compounds consistent with the degradation of root exudates and complex aromatic compounds, were identified by gas chromatography/mass spectrometry (GC/MS) in sediment samples under the mature cottonwood tree. Elsewhere at the site, transpiration and degradation by the cottonwood trees appears to be responsible for loss of chlorinated ethenes.     

地下水脱卤过程中的微生物种间代谢互作：提高原位氯代烯烃厌氧脱氯效能的有效途径

有机卤呼吸细菌(organohalide-respiring bacteria, OHRB)在氯代烯烃污染地下水的原位生物修复中扮演着关键性的角色,提高其丰度及活性对氯代烯烃的完全去除具有重要意义。在实际环境中,有机卤呼吸细菌往往与多种微生物共存,微生物种间代谢互作现象十分普遍,有机污染物的完全无害化往往需要通过微生物菌群的协同代谢作用来实现。因此,本文围绕微生物种间代谢互作进行综述,对目前获得的脱氯微生物菌种资源及脱氯机理进行了回顾,重点阐述了专性OHRB、非专性OHRB和非OHRB的种间代谢互作行为及机制,并提出以种间代谢互作为指导进行合成微生物群落的构建来有效提高氯代烯烃厌氧生物降解效率,为实现环境氯代烯烃类有机污染物的快速、彻底无害化提供理论指导。     

Modeling Chlorinated Solvent Bioremediation Using Hydrogen Release Compound (HRC)

Chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE) are common groundwater contaminants. One approach that has been used to manage these contaminants is in situ bioremediation, where an electron donor is added to contaminated groundwater to stimulate indigenous bacteria to degrade the chlorinated compounds. A technique that is increasingly being used to supply electron donor to the subsurface involves application of a commercial product with the trade name Hydrogen Release Compound (HRC). HRC is a viscous fluid that releases lactic acid, which subsequently is metabolized to provide molecular hydrogen as an electron donor. This study investigates application of HRC to remediate a site contaminated with TCE. A user-defined dual-Monod biodegradation reaction module was developed for the RT3D-reactive transport code to simulate in situ biodegradation of TCE by reductive dehalogenation stimulated by release of molecular hydrogen in the subsurface as a result of HRC injection. The model was used to show how a remediation system using HRC to stimulate reductive dehalogenation could be designed, and how mixing, as quantified by hydraulic conductivity and dispersivity, impacts the system design.     

Biotransformation of Trichloroethylene Using Butane-Oxidizing Bacteria

Mixed butane-utilizing cultures were obtained through sequential batch enrichment under 6% (vol/vol) butane in air using one sediment and four different soil samples with varying histories of contamination as inocula. Subsamples of each environmental sample were subjected to one of three pretreatments prior to inoculation: saturation with 30% ethanol, a 15-min exposure to 60°C, or no treatment. Thirteen of the 14 mixed cultures that were obtained appeared to cometabolize trichloroethylene (TCE) while growing at the expense of butane. All 13 caused a loss of at least one-third of TCE from initial aqueous levels between 4 and 25?µg/ml during 6 days of growth on butane provided at initial aqueous concentrations between 90 and 160?µg/ml. Two cultures cometabolized essentially all the available TCE during this test. One culture, which was obtained from an ethanol-pretreated inoculum, vigorously consumed butane while leaving TCE levels essentially unchanged. However, two other mixed cultures originally derived from the same environmental sample as the ineffective culture were moderately active in TCE cometabolism. Thus, TCE-cometabolizing butane oxidizers appeared to be present in all five of the environmental samples used in these studies.     

Intrinsic bioremediation in a solvent-contaminated alluvial groundwater

An industrial site contaminated with a mixture of volatile organic compounds in its subsurface differed from previously reported locations in that the contamination consisted of a mixture of chlorinated, brominated, and non-halogenated aromatic and aliphatic solvents in an alluvial aquifer. The source area was adjacent to a river. Of the contaminants present in the aquifer, benzene, toluene, and chlorobenzene (BTC) were of primary concern. Studies of the physical, chemical, and microbiological characteristics of site groundwater were conducted. The studies concentrated on BTC, but also addressed the fate of the other aquifer VOCs. Gas chromatographic analyses performed on laboratory microcosms demonstrated that subsurface microorganisms were capable of BTC degradation. Mineralization of BTC was demonstrated by the release of ¹⁴CO₂ from radiolabelled BTC. In the field, distribution patterns of nutrients and electron acceptors were consistent with expression of in situ microbial metabolic activity: methane, conductivity, salinity and o-phosphate concentrations were all positively correlated with contaminant concentration; while oxidation-reduction potential, nitrate, dissolved oxygen and sulfate concentrations were negatively correlated. Total aerobes, aerotolerant anaerobes, BTC-specific degraders, and acridine orange direct microscopic microorganism counts were strongly and positively correlated with field contaminant concentrations. The relative concentrations of benzene and toluene were lower away from the core of the plume compared to the less readily metabolized compound, chlorobenzene. Hydrodynamic modeling of electron-acceptor depletion conservatively estimated that 450 kg of contaminant have been removed from the subsurface yearly. Models lacking a biodegradation term predicted that 360 kg of contaminant would reach the river annually, which would result in measurable contaminant concentrations. River surveillance, however, has only rarely detected these compounds in the sediment and then only at trace concentrations. Thus, the combination of field modeling, laboratory studies, and site surveillance data confirm that significant in situ biodegradation of the contaminants has occurred. These studies establish the presence of intrinsic bioremediation of groundwater contaminants in this unusual industrial site subsurface habitat. Received 01 December 1995/ Accepted in revised form 27 July 1996     

Modeling of a Field Experiment on Bioremediation of Chlorobenzenes in Groundwater

The aquifer below an abandoned chemical plant in Hamburg, Germany, is heavily contaminated with chlorinated aromatic compounds, mainly chlorobenzenes. Preliminary evaluations made evident that pump-and-treat remediation of the site would be inefficient due to adsorption of the contaminants and the possible presence of dense nonaqueous phase liquid (DNAPL) in the aquifer. Other preliminary studies indicated that benzenes with a low degree of chlorination, which account for the bulk of the contamination in the aquifer, were aerobically degradable. Thus, in situ bioremediation using dissolved oxygen as an oxidant was proposed as an alternative to pump-and-treat remediation.

To assess the feasibility of bioremediation at this site, a pilot study was conducted on a 55 m x 30 m test plot that was equipped with two injection wells, six extraction wells, and 18 observation wells. Water saturated with oxygen using pure oxygen gas was injected for a period of 433 days.

Application of the three-dimensional reactive transport model, Transport, Biochemistry, and Chemistry (TBC), allowed the distinction between transport and reactive processes and the evaluation of oxygen consuming processes. Preliminary mass balance considerations had indicated that a significant portion of the injected oxygen was used for oxidation of inorganic compounds instead of the contaminants. The model calculations allowed quantification of these effects. Simulation results suggested that in situ bioremediation occurred at the site, but with an unacceptably low efficiency. Only 2% of the injected oxygen was used for contaminant degradation, while 63% was consumed by inorganic reductants, presumably mainly pyrite. Approximately 32% of the injected oxygen was extracted by the extraction wells and approximately 3% remained in the aquifer after the pilot study was completed.     

异养同化降解氯代烃的研究现状、微生物代谢特性及展望

氯代烃(Chlorinated hydrocarbons,CAHs)污染遍布全球,其三致效应和遗传毒性对人类健康和生态环境构成重大威胁。CAHs异养同化具有降解彻底、无二次污染和降解效率高的特点,全面认识CAHs异养同化过程,对于强化和应用异养同化降解,扩大CAHs的修复途径具有重要的推动作用。文中首先分析了微生物细胞异养同化降解CAHs主要方式,阐述了异养同化的两大优势;针对CAHs异养同化的研究现状进行了系统性的总结,明确了可发生异养同化作用的CAHs种类及特征;基于氯代烷烃、氯代烯烃和氯代芳烃分类,概述了异养同化微生物的主要菌属及代谢特征;针对典型氯代烃,系统分析了参与代谢过程关键酶及特征基因,归纳了异养同化代谢途径;最后,根据当前研究现状对异养同化研究存在的问题进行了综述并对未来的发展方向进行了展望。     

Phreatophyte influence on reductive dechlorination in a shallow aquifer contaminated with trichloroethene (TCE)

Phytoremediation uses the natural ability of plants to degrade contaminants in groundwater. A field demonstration designed to remediate aerobic shallow ground‐water contaminated with trichloroethene began in April 1996 with the planting of cottonwood trees, a short‐rotation woody crop, over an approximately 0.2‐ha area at the Naval Air Station, Fort Worth, Texas. The project was developed to demonstrate capture of contaminated groundwater and degradation of contaminants by phreatophytes. Analyses from samples of groundwater collected from July 1997 to June 1998 indicate that tree roots have the potential to create anaerobic conditions in the groundwater that will facilitate degradation of trichloroethene by microbially mediated reductive dechlorination. Organic matter from root exudates and decay of tree roots probably stimulate microbial activity, consuming dissolved oxygen. Dissolved oxygen concentrations, which varied across the site, were smallest near a mature cottonwood tree (about 20 years of age and 60 meters southwest of the cottonwood plantings) where degradation products of trichloroethene were measured. Oxidation     

Selecting Remediation Goals by Assessing the Natural Attenuation Capacity of Groundwater Systems

Remediation goals for the source areas of a chlorinated ethene-contaminated groundwater plume were identified by assessing the natural attenuation capacity of the aquifer system. The redox chemistry of the site indicates that sulfate-reducing (H₂ ∼ 2 nanomoles [nM]) per liter conditions near the contaminant source grade to Fe(III)-reducing conditions (H₂ ∼ 0.5 nM) downgradient of the source. Sulfate-reducing conditions facilitate the initial reduction of perchloroethene (PCE) to trichloroethene (TCE), cis-dichloroethene (cis-DCE), and vinyl chloride (VC). Subsequently, the Fe(III)-reducing conditions drive the oxidation of cis-DCE and VC to carbon dioxide and chloride. This sequence gives the aquifer a substantial capacity for biodegrading chlorinated ethenes. Natural attenuation capacity (the slope of the steady-state contaminant concentration profile along a groundwater flowpath) is a function of biodegradation rates, aquifer dispersive characteristics, and groundwater flow velocity. The natural attenuation capacity at the Kings Bay, Georgia site was assessed by estimating groundwater flowrates (∼0.23±0.12 m/d) and aquifer dispersivity (∼1 m) from hydrologic and scale considerations. Apparent biodegradation rate constants (PCE and TCE ∼0.01 d^-1; cis-DCE and VC ∼0.025 d^-1) were estimated from observed contaminant concentration changes along aquifer flowpaths. A boundary-value problem approach was used to estimate levels to which contaminant concentrations in the source areas must be lowered (by engineered removal), or groundwater flow velocities lowered (by pumping) for the natural attenuation capacity to achieve maximum concentration limits (MCLs) prior to reaching a predetermined regulatory point of compliance.     

Role of sulfate in microbial transformations of environmental contaminants: Chlorinated aromatic compounds

Despite recent progress made in describing microbial transformations that occur under anaerobic conditions, our understanding of the role sulfate‐reducing bacteria may play in the remediation of environmental contaminants is still very limited. The objective of this mini‐review is to summarize what is currently known of the metabolism of chlorinated aromatic compounds in the presence of sulfate. Sulfidogenic processes are discussed with respect to the thermodynamics of haloaromatic oxidation and to their potential use in the in situ bioremediation of hazardous organic wastes. A comprehensive listing is made of anaerobic transformations that involve both halogenated and nonhalogenated monoaromatic substrates by denitrifiers, dissimilatory iron‐reducing bacteria, and methanogenic consortia. In contrast to other anaerobic processes, studies involving sulfate‐mediated metabolism of hazardous organic compounds have been neglected; however, the recent success in defining methanogenic transformations, in particular, has enhanced expectations of defining an analogous role for sulfate‐reducing microbial communities in low redox environments that have become contaminated with hazardous substances.     

Metabolic indicators for detecting in situanaerobic alkylbenzene degradation

Monitoring programs for intrinsic bioremediation of fuel hydrocarbonsrequire indicators that can convincingly demonstrate in situ metabolism. In this evaluation of potential indicators of in situ anaerobic alkylbenzene metabolism, laboratory and field data are reviewed for two classes of aromatic acids: (i) benzylsuccinate, E-phenylitaconate, and their methyl homologs, and (ii) benzoate, and methyl-, dimethyl-, and trimethylbenzoates. The review includes previously unpublished field data from a hydrocarbon-contaminated site in Fallon (Nevada), at which both classes of metabolites were detected in groundwater. The two classes of compounds were evaluated with respect to specificity (i.e., unique biochemical relationship to a specific alkylbenzene), stability, and generation as degradation intermediates versus dead-end products; recent developments in the biochemistry of anaerobic toluene and xylene degradation were incorporated in this evaluation. In general, benzylsuccinates/E-phenylitaconates are superior to benzoates in terms of their very high specificity to their parent hydrocarbons and their lack of commercial and industrial sources. They are also uniquely indicative of anaerobic conditions. All of the benzoates, benzylsuccinates, and E-phenylitaconates are relatively stable chemically and (with the exceptionof benzoate) biologically under anaerobic conditions, based on the limited data available. Although benzoate, benzylsuccinate, and E-phenylitaconate are intermediates of anaerobic toluene mineralization to carbon dioxide, their methyl homologs can be either mineralization intermediates or cometabolic dead-end products of alkylbenzenes, depending on the bacteria involved. Benzoates are far more commonly reported in field studies of hydrocarbon-contaminated aquifers than are benzylsuccinates and E-phenylitaconates, although it is not clear whether this is an accurate representation of the relative occurrenceof these metabolites at contaminated sites, or whether it instead reflects the limited range of target analytes used in most field studies to date.     

专一营养与兼性甲烷氧化菌降解氯代烃的研究现状、动力学分析及展望

生物修复技术被认为是氯代烃类污染物处理处置的最有效途径之一,而甲烷氧化菌在该领域表现出较大的应用潜力。近期研究发现,突破了仅能利用单碳化合物的局限,兼性甲烷氧化菌能够利用多种底物降解氯代烃,这一独特的新陈代谢特性,使其在污染物生物处置领域逐渐受到关注。结合本课题组研究成果,对甲烷氧化菌降解氯代烃进行了全面总结,主要包括:分析了不同菌株(纯菌株和混合菌株)对不同氯代烃的降解效果;比较了不同类型甲烷单加氧酶在不同底物体系中的活性表达和催化特性;总结了模型菌株甲基弯菌Methylosinus trichosporium OB3b降解氯代烃的动力学特性;概述了兼性甲烷氧化菌株降解氯代烃的特性及其应用潜力;最后讨论了甲烷氧化菌降解氯代烃存在的问题及未来发展方向。     

Design and Validation of ureC-based Primers for Groundwater Detection of Urea-Hydrolyzing Bacteria

Polymerase chain reaction primers based on the ureC gene are described for use in detecting diverse groundwater urea-hydrolyzing bacteria. Six degenerate primers were designed and evaluated for their ability to detect the gene encoding the large catalytic subunit of urease, ureC. Five combinations of these primers were tested pair-wise and displayed an overlapping detection range for bacterial isolates. Pair L2F/L2R exhibited the greatest detection range for described bacterial species and for bacterial isolates from groundwater samples belonging to the bacterial divisions Firmicutes, Actinobacteria, and the α , β , and γ subdivisions of Proteobacteria. Primers L2F/L2R exhibited a greater detection range than previously described ureC-specific primers, and amplified novel ureC sequences from groundwater isolates in the genera Hydrogenophaga, Acidovorax, Janthinobacterium, and Arthrobacter. A comparative phylogenetic analysis of ureC and 16S rRNA genes was performed to determine the utility of groundwater ureC sequence information as a phylogenetic marker for ureolytic species. Our results were consistent with previous analyses of urease genes which demonstrated that the ureC gene has undergone lateral transfer and is not a robust phylogenetic marker. However, the ureC-specific primers, L2F/L2R, demonstrate a broad detection range for ureolytic species, and can serve to enhance functional diversity analyses of ureolytic bacteria.