In situ measurements of volatile aromatic hydrocarbon biodegradation rates in groundwater

Benzene and alkylbenzene biodegradation rates and patterns were measured using an in situ microcosm in a crude-oil contaminated aquifer near Bemidji, Minnesota. Benzene-D6, toluene, ethylbenzene, o-, m- and p-xylenes and four pairs of C₃- and C₄-benzenes were added to an in situ microcosm and studied over a 3-year period. The microcosm allowed for a mass-balance approach and quantification of hydrocarbon biodegradation rates within a well-defined iron-reducing zone of the anoxic plume. Among the BTEX compounds, the apparent order of persistence is ethylbenzene > benzene > m,p-xylenes > o-xylene ≥ toluene. Threshold concentrations were observed for several compounds in the in situ microcosm, below which degradation was not observed, even after hundreds of days. In addition, long lag times were observed before the onset of degradation of benzene or ethylbenzene. The isomer-specific degradation patterns were compared to observations from a multi-year study conducted using data collected from monitoring wells along a flowpath in the contaminant plume. The data were fit with both first-order and Michaelis-Menten models. First-order kinetics provided a good fit for hydrocarbons with starting concentrations below 1 mg/L and Michaelis-Menten kinetics were a better fit when starting concentrations were above 1 mg/L, as was the case for benzene. The biodegradation rate data from this study were also compared to rates from other investigations reported in the literature.     

芳香类污染物的厌氧生物降解研究

综述了国内外芳香类污染物厌氧降解的研究进展,详细阐述了含氮芳香类、氯代芳香类和酚类污染物厌氧降解的微生物类群与机理.提出了芳香类污染物生物降解今后发展方向的重点是共基质条件下生物降解性研究、厌氧-好氧条件下的生物降解性研究、高效工程菌和固定化细胞技术应用研究、构建基因工程菌和遗传学研究等技术领域.     

Transport of reactive colloids and contaminants in groundwater: effect of nonlinear kinetic interactions

Transport of reactive colloids in groundwater may enhance the transport of contaminants in groundwater. Often, the interpretation of results of transport experiments is not a simple task as both reactions of colloids with the solid matrix and reactions of contaminants with the solid matrix and mobile and immobile colloids may be time dependent and nonlinear. Further colloid transport properties may differ from solute transport properties. In this paper, a one-dimensional model for coupled and contaminant in a porous medium (COLTRAP) is presented together with simulation results. Calculated breakthrough curves (BTC's) during contamination and decontamination show systematically the effect of nonlinear and kinetic interactions on contaminant transport in the presence of reactive colloids, and the effect of colloid transport properties that differ from solute transport properties. It is shown that in case of linear kinetic reactions, the rate of exchange of mobile and immobile colloids have a large impact on the shape of BTC's even if the solid matrix is saturated with respect to colloids. BTC's during the contamination and decontamination phase have identical shapes in this case. Moreover, the slow reactions of contaminants and colloids may lead to unretarded breakthrough of contaminants. Independent of reaction rates, nonlinear reactions lead to BTC's that are steeper during contamination than in the linear case. A characteristic aspect of nonlinear sorption is that shapes of BTC's differ during the contamination and decontamination phase. It has been observed that shapes of some of the simulated adsorption and desorption curves are similar as shapes found in experiments reported in literature. This stresses the importance of incorporating both kinetics and nonlinearity in models for coupled colloid and contaminant transport and the capability of COLTRAP to interpret experimental results. Finally, to figure out whether nonlinear processes play a role, it is very important to consider both contamination and decontamination in transport experiments.     

Levels of major organochlorine contaminants in sequentially - laid Herring Gull eggs

Sequentially laid eggs of Herring Gulls in Lake Erie and the Detroit River (Ontario) were found to contain increasingly higher levels of organochlorine contaminants. The reason for this was not determined but a depletion of lipid pools during the egg laying period and a rapid equilibrium between body and egg burdens may explain the results. It is recommended that, for long term toxic residue monitoring, eggs at the same position in the order of laying be taken from all sampled clutches.     

Modelling of physical and reactive processes during biodegradation of a hydrocarbon plume under transient groundwater flow conditions

Numerical experiments of non-reactive and reactive transport were carried out to quantify the influence of a seasonally varying, transient flow field on transport and natural attenuation at a hydrocarbon-contaminated field site. Different numerical schemes for solving advective transport were compared to assess their capability to model low transversal dispersivities in transient flow fields. For the field site, it is shown that vertical plume spreading is largely inhibited, particularly if sorption is taken into account. For the reactive simulations, a biodegradation reaction module for the geochemical transport model PHT3D was developed. Results of the reactive transport simulations show that under the site-specific conditions the temporal variations in groundwater flow do, to a modest extent, affect average biodegradation rates and average total (dissolved) contaminant mass in the aquifer. The model simulations demonstrate that the seasonal variability in groundwater flow only results in significantly enhanced biodegradation rates when a differential sorption of electron donor (toluene) and electron acceptor (sulfate) is assumed.     

In situ sequenced bioremediation of mixed contaminants in groundwater

A mixture of chlorinated solvents (about 0.5-10 mg/l), including tetrachloroethene (PCE) and carbon tetrachloride (CT), together with a petroleum hydrocarbon, toluene (TOL), were introduced into a 24 m long x 2 m wide x 3 m deep isolated section (henceforth called a gate) of the Borden aquifer and subjected to sequential in situ treatment. An identical section of aquifer was similarly contaminated and allowed to self-remediate by natural attenuation, thus serving as a control. The control presents a rare opportunity to critically assess the performance of the treatment systems, and represents the first such study for sequenced in situ remediation. The first treatment step was anaerobic bioremediation. This was accomplished using a modified nutrient injection wall (NIW) to pulse benzoate and a nutrient solution into the aquifer, maximizing mixing by dispersion and minimizing fouling near the injection wells. In the anaerobic bioactive zone that developed, PCE, CT and chloroform (CF), a degradation product of CT, degraded with a half-lives of about 59, 5.9 and 1.7 days, respectively. The second step was aerobic bioremediation, using a biosparge system. TOL and cis-1,2 dichloroethene (cDCE), from PCE degradation, were found to degrade aerobically with half-lives of 17 and 15 days, respectively. Compared to natural attenuation, PCE and TOL removal rates were significantly better in the sequenced treatment gate. However, CT and CF were similarly and completely attenuated in both gates. It is believed that the presence of TOL helped sustain the reducing environment needed for the reduction of these two compounds.     

地下水中污染物运移过程数值模拟算法的比较

数值模拟已成为目前地下水有机污染现场中,预测和评价溶解相有机污染物运移的主要手段.自从MT3D问世以来,它在地下水溶质运移的模拟中得到了广泛的应用.MT3D中包含有4种不同的数值算法--MOC,MMOC,HMOC和UFDM.利用Processing MODFLOW Pro.7.0.5建立了均质一维流动的地下水数学模型,考虑溶解相有机污染物在地下水中运移时的4个主要影响因素--对流、弥散、吸附和降解,设定了14种代表性的情形,模拟了等浓度污染源条件下污染物的运移,并将不同数值算法的计算结果与理论解进行比较,从而研究不同数值算法的优缺点,为实际数值模拟时算法的选择提供依据.     

Pilot-scale demonstration of a two-stage methanotrophic bioreactor for biodegradation of trichloroethylene in groundwater

A two-stage methanotrophic bioreactor system was developed for remediation of water contaminated with TCE and other chlorinated, volatile, aliphatic hydrocarbons. The first stage of the reactor was a suspended-growth culture vessel using a bubbleless methane-transfer device. The second stage was a plug-flow bioreactor supplied with contaminated groundwater and cell suspension from the culture vessel. The test objectives were to determine the applicability of microbial culture conditions reported in the literature for continuous, pilot-scale TCE treatment; the technical feasibility of plug-flow bioreactor design for treatment of TCE; and the projected economic competitiveness of the technology considering the cost of methane for growth of methanotrophs. The methanotrophic organism used in the study was Methylosinus trichosporium OB3b. Information on system operation was obtained in bench tests prior to conducting the pilot tests. In bench- and pilot-scale tests, variability in the degree of TCE degradation and difficulty in maintaining the microbial culture activity led to short periods of satisfactory biotreatment. Further development of the microbial culture system will be required for long-term operation. During transient periods of high TCE degradation activity, the bioreactor concept proved feasible by exhibiting both a high degree of TCE biodegradation (typically about 90% at influent TCE concentrations of 0.5-4 ppm) and a close approximation to first-order reactor kinetics throughout the length of the reactor. Actual methane usage in the pilot-scale reactor resulted in projected methane costs of $0.33 per 1000 gallons of water treated. This cost theoretically would be reduced by system modifications. The theoretical minimum methane cost was approximately $0.05 per 1000 gallons.     

Analytical solutions for multiple species reactive transport in multiple dimensions

Many numerical computer codes used to simulate multi-species reactive transport and biodegradation have been developed in recent years. Such numerical codes must be validated by comparison of the numerical solutions with an analytical solution. In this paper, a method for deriving analytical solutions of the partial differential equations describing multiple species multi-dimensional transport with first-order sequential reactions is presented. Although others have developed specific solutions of multi-species transport equations, here a more general analytical approach, capable of describing any number of reactive species in multiple dimensions is derived. A substitution method is used to transform the multi-species reactive transport problem to one that can be solved using previously published single-species solutions for various initial and boundary conditions. One- and three-dimensional examples are presented to illustrate the steps involved in extending single-species solutions to a four-species system with sequential first-order reactions.     

Metals and emerging contaminants in groundwater and human health risk assessment

Environmental Science and Pollution Research - Groundwaters are normally consumed without previous treatment and therefore the monitoring of contaminants in order to guarantee its safety is...     

一种新嗜冷菌JLNY02降解地下水中阿特拉津的研究

从某农药厂排污口采集污泥样品，通过富集培养，从中分离筛选出一株阿特拉津高效降解菌JLNY02，并进一步对其降解的影响因素进行研究。在10℃的条件下降解阿特拉津，其降解率可达81.8%，而在高温下的降解率较低，仅31．4％。     

Dimension reduction and source identification for multispecies groundwater contamination

Assessment of chemical contamination at large industrial complexes with long and sometimes unknown histories of operation represents a challenging environmental problem. The spatial and temporal complexity of the contaminant may be due to changes in production processes, differences in the chemical transport, and the physical heterogeneity of the soil and aquifer materials. Traditional mapping techniques are of limited value for sites where dozens of chemicals with diverse transport characteristics may be scattered over large spatial areas without documentation of disposal histories. In this context, a site with a long and largely undocumented disposal history of shallow groundwater contamination is examined using principal component analysis (PCA). The dominant chemical groups and chemical "modes" at the site were identified. PCA results indicate that five primary and three transition chemical groups can be identified in the space of the first three eigenvectors of the correlation matrix, which account for 61% of the total variance of the data. These groups represent a significant reduction in the dimension of the original data (116 chemicals). It is shown that each group represents a class of chemicals with similar chemo-dynamic properties and/or environmental response. Finally, the groups are mapped back onto the site map to infer delineation of contaminant source areas for each class of compounds. The approach serves as a preliminary step in subsurface characterization, and a data reduction strategy for source identification, subsurface modeling and remediation planning.     

Assessment of in situ biodegradation of monochlorobenzene in contaminated groundwater treated in a constructed wetland

The degradation of monochlorobenzene (MCB) was assessed in a constructed wetland treating MCB contaminated groundwater using a detailed geochemical characterisation, stable isotope composition analysis and in situ microcosm experiments. A correlation between ferrous iron mobilisation, decreasing MCB concentration and enrichment in carbon isotope composition was visible at increasing distance from the inflow point, indicating biodegradation of MCB in the wetland. Additionally, in situ microcosm systems loaded with 13C-labelled MCB were deployed for the first time in sediments to investigate the biotransformation of MCB. Incorporation of 13C-labelled carbon derived from the MCB into bacterial fatty acids substantiated in situ degradation of MCB. The detection of 13C-labelled benzene indicated reductive dehalogenation of MCB. This integrated approach indicated the natural attenuation of the MCB in a wetland system. Further investigations are required to document and optimise the in situ biodegradation of MCB in constructed and natural wetland systems treating contaminated groundwater.     

Bioavailability of contaminants estimated from uptake rates into soil invertebrates

It is often argued that the concentration of a pollutant inside an organism is a good indicator of its bioavailability, however, we show that the rate of uptake, not the concentration itself, is the superior predictor. In a study on zinc accumulation and toxicity to isopods (Porcellio scaber) the dietary EC(50) for the effect on body growth was rather constant and reproducible, while the internal EC(50) varied depending on the accumulation history of the animals. From the data a critical value for zinc accumulation in P. scaber was estimated as 53 microg/g/wk. We review toxicokinetic models applicable to time-series measurements of concentrations in invertebrates. The initial slope of the uptake curve is proposed as an indicator of bioavailability. To apply the dynamic concept of bioavailability in risk assessment, a set of representative organisms should be chosen and standardized protocols developed for exposure assays by which suspect soils can be evaluated.     

Estimating spatially-variable first-order rate constants in groundwater reactive transport systems

Numerical reactive transport models are often used as tools to assess aquifers contaminated with reactive groundwater solutes as well as investigating mitigation scenarios. The ability to accurately simulate the fate and transport of solutes, however, is often impeded by a lack of information regarding the parameters that define chemical reactions. In this study, we employ a steady-state Ensemble Kalman Filter (EnKF), a data assimilation algorithm, to provide improved estimates of a spatially-variable first-order rate constant λ through assimilation of solute concentration measurement data into reactive transport simulation results. The methodology is applied in a steady-state, synthetic aquifer system in which a contaminant is leached to the saturated zone and undergoes first-order decay. Multiple sources of uncertainty are investigated, including hydraulic conductivity of the aquifer and the statistical parameters that define the spatial structure of the parameter field. For the latter scenario, an iterative method is employed to identify the statistical mean of λ of the reference system. Results from all simulations show that the filter scheme is successful in conditioning the λ ensemble to the reference λ field. Sensitivity analyses demonstrate that the estimation of the λ values is dependent on the number of concentration measurements assimilated, the locations from which the measurement data are collected, the error assigned to the measurement values, and the correlation length of the λ fields.     

修复铬污染地下水的可渗透反应墙介质筛选

通过实验研究筛选出一种经济、高效的用于修复铬污染地下水的可渗透反应墙(PRB)介质。实验以铬污染地下水为研究对象,分别对Fe0、Fe0+石英砂和包覆型零价铁填料进行了筛选实验,选取处理效果好且经济可行的包覆型零价铁材料作为PRB反应介质。结果表明,以包覆型零价铁材料作为PRB反应介质,大大提高了铁粉的利用效率,且缓解了系统堵塞严重的问题。以包覆型零价铁材料作为PRB反应介质修复Cr(VI)污染地下水是可行的。     

Bioassay-directed identification of toxic organic compounds in creosote-contaminated groundwater

Despite the fact that creosote mainly consists of polycyclic aromatic hydrocarbons (PAHs), more polar compounds like phenolics, benzenes and N-, S-, O-heterocyclics dominate the groundwater downstream from creosote-contaminated sites. In this study, bioassay-directed fractionation, combined with fullscan GC-MS, identified organic toxicants in creosote-contaminated groundwater. An organic extract of creosote-contaminated groundwater was fractionated on a polar silica column using high performance liquid chromatography (HPLC), and the toxicity of the fractions was measured by the Microtox-bioassay. PAHs, which comprise up to 85% of pure creosote, accounted for only about 13% of total toxicity in the creosote-contaminated groundwater, while methylated benzenes, phenolics and N-heterocyclics accounted for ca. 80% of the measured toxicity. The fraction containing alkylated quinolines was the most toxic single fraction, accounting for 26% of the total measured toxicity. The results imply that focus on PAHs may underestimate risks associated with creosote-contaminated groundwater, and that environmental risk assessment should focus to a higher degree on substituted PAHs and phenolics because they are more toxic than the unsubstituted ones. Additionally, benzenes and N-heterocyclics (e.g., alkylated quinolines) should be assessed.     

污染土壤及地下水修复的PRB技术及展望

PRB技术是一类就地修复污染土壤及地下水的新型技术 ,主要由注入井、浸提井和监测井3部分所组成。污染地区的水文地质学研究 ,是实施该技术的关键 ;化学活性物质的筛选、注入的部位、浓度、速率以及是否均匀分布 ,是该技术是否有效的关键要素。胶态零价铁PRB技术 ,被证明是一项修复由卤代烃、卤代芳烃和有机氯农药以及一些有毒金属 (如铬、硒、铀、砷和锝等 )引起的土壤及地下水污染的有效技术。尽管这些技术存在一定的弊病 ,但与传统的处理方法相比 ,其技术上的优势是十分明显的。可以预料 ,这一技术在我国有良好的应用前景     

复合介质渗透反应格栅去除地下水中的氨氮

针对受低浓度氨氮污染的地下水,实验筛选组合了不同的反应介质,利用串联的多介质填充柱模拟渗透反应格栅,通过物理吸附及生物硝化-反硝化作用来实现氮的去除。结果表明,在进水氨氮浓度为10 mg/L、流速为0.5 m/d的条件下,模拟柱对氨氮的去除率达到98%以上,且不会出现亚硝酸盐及硝酸盐浓度的升高。水体经过释氧柱后溶解氧由2mg/L升高至10 mg/L以上,表明释氧材料可提供硝化细菌所需的好氧环境。好氧柱中填充易于生物挂膜的生物陶粒及对氨氮有较强吸附能力的沸石,二者联用通过生物硝化-物理吸附协同作用实现对氨氮的去除,其中生物作用实现的氨氮去除量占总去除量的50%左右。后续厌氧反应柱填充海绵铁除氧并利用松树皮颗粒作为碳源,创造反硝化菌生长条件,硝酸盐氮浓度可由10 mg/L降低至5 mg/L以下,实现对好氧反应阶段所产生的硝酸盐的去除,避免了地下水的二次污染。     

Sequential coupling of bio-augmented permeable reactive barriers for remediation of 1,1,1-trichloroethane contaminated groundwater

Sequential coupling of high-density luffa sponge (HDLS) immobilized microorganism and permeable reactive barriers (IM Bio-PRBs) was superior to intimate coupling of free microorganism and permeable reactive barriers (FM Bio-PRBs) for remediation of 1,1,1-trichloroethane contaminated groundwater. IM Bio-PRBs had much better performance to removal 1,1,1-trichloroethane (1,1,1-TCA) and prevent the transport of 1,1,1-TCA and inorganic ions (NO₃^?, PO₄^3?, and SO₄^2?). The majority of them were prevented and accumulated in upgradient of IM Bio-PRBs. 1,1,1-TCA and inorganic ions in there contributed to the much faster growth of microorganism in upgradient aquifer. Therefore, the removal of 1,1,1-TCA and consumption of inorganic ions in upgradient of Bio-PRBs played a constructive role in reducing the processing load of following zero-valent iron (ZVI) PRBs and the negative effect of free microorganism cells (biological clogging) and inorganic ions (chemical clogging) on Bio-PRB permeability. In addition, IM Bio-PRBs were more conducive to accelerate the removal of 1,1,1-TCA in long-term remediation and 1,1,1-TCA residual concentration significantly lower than the safety standard of 0.2 mg L^?1. The change of terminal by-products of 1,1,1-TCA contaminated groundwater in Bio-PRBs showed that 1,1,1-TCA could be effectively de-chlorinated and mineralized in Bio-PRBs. The reductant H₂S (prolong the service life of ZVI-PRBs) was much more produced and utilized in IM Bio-PRBs. Taken together, sequentially coupled IM Bio-PRBs had a better overall performance, and its service life could be prolonged. It was a different design and idea to update conventional PRB remediation technology and theory.