Natural attenuation of chloroethenes: identification of sequential reductive/oxidative biodegradation by microcosm studies

A different lines of evidence approach for investigation of biodegradation processes at a chloroethene contaminated site showed well corresponding results of pollutant profiles, redox zonation, characterisation of autochthonic microflora and microcosm studies. In particular microcosm studies allowed identification of the predominating degradation pathways. Perchloroethene and trichloroethene are reductively chlorinated to mainly cis-1,2-dichloroethene (cDCE) under anaerobic conditions. Further reductive degradation to vinyl chloride (VC) is restricted to a distinct strongly anaerobic zone in the plume. Addition of high amounts of sediment material (80 vol%) to groundwater microcosms enabled reductive dechlorination without amendment with further auxiliary substrates. Reductive dechlorination was not irreversibly hindered by initially high nitrate concentrations and initially high oxidation-reduction potential. The products of anaerobic degradation cDCE and VC are subsequently aerobically mineralised, even when only low oxygen concentrations are available. Anaerobic oxidative degradation could not be proven in this study.     

Synergetic degradation of Fe/Cu/C for groundwater polluted by trichloroethylene

This study investigated the enhancement of synergetic degradation of Fe/Cu/C (Fe: commercial iron, Cu: solid product of Fe reacted with CuSO(4), C: carbon powder) for simulated groundwater contaminated by trichloroethylene (TCE). Zero valent iron (ZVI) as a reducing agent was proved to be effective for TCE removal. The Fe/Cu/C system resulted in higher reduction efficiency as a result of the synergetic role of Fe/Cu and Fe/C microelectrode than the Fe (ZVI) or Fe/Cu system, and the half-life was only about 0.4 h. When m(Fe) achieved 12.5 g L(-1), the residual concentration of TCE almost leveled off. Fe:Cu = 10:1 or m(C) = 0.0086 g can induce the optimum function for TCE degradation. A neutral condition was appropriate for TCE degradation, and an acidic system slightly favored TCE dechlorination compared with an alkaline system. GC/MS analysis indicated that TCE was dechlorinated to 1,1-dichloroethene (1,1-DCE), cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC), and 1,1-DCE might be the precursor. Fe/Cu/C reduction is a highly promising technique for TCE removal, and it is an excellent alternative to enhance TCE reductive dechlorination.     

Stimulation of reductive dechlorination for in situ bioremediation of a soil contaminated with chlorinated ethenes

A soil from a former chemical redistribution company, contaminated with mainly chlorinated aliphatics, was studied for bioremediation purposes. Groundwater analyses revealed that the original pollutants, i.e. tetrachloroethene (PCE) and trichloroethene (TCE), were present at levels ranging from 2.3 to 122 mg/L. Dichloroethene (DCE), vinylchloride (VC), ethene and ethane were also detected at significant concentrations although they had never been introduced to the soil. Relatively high concentrations of cisDCE as compared to trans-DCE and 1,1-DCE indicated that a slow in situ biodegradation had taken place by reductive dechlorination. Laboratory experiments with flow-through soil columns were performed to determine the optimal conditions for the enhancement of reductive dechlorination by the indigenous dechlorinating population. The addition of single electron donors to artificial groundwater resulted in the dechlorination of PCE to TCE and cis-DCE, whereas complete dechlorination to ethene was solely achieved with compost extract added to native groundwater.     

Coupled reduction of chlorinated hydrocarbons and heavy metals by zerovalent silicon.

The feasibility of using zerovalent silicon (Si0) as a novel reductant to remove chlorinated compounds and heavy metals in contaminated sites was investigated. The kinetics and degradation mechanism of carbon tetrachloride (CT) by Si0 were also examined. Results showed that zerovalent silicon could effectively dechlorinate the chlorinated compounds. A nearly complete dechlorination of CT by Si0 was obtained within 14 h. The produced concentrations of chloroform (CF) accounted for 71-88% loss of CT, showing that reductive dechlorination is the major degradation pathway for the degradation of chlorinated hydrocarbons by Si0. The degradation followed pseudo first-order kinetics and the normalized surface reaction rate constant (k(sa)) for CT dechlorination ranged between 0.0342 and 0.0454 L m(-2) h(-1) when CT concentrations were in the range of 3-20 microM. A linear relationship between the k(sa) and pH value was also established. In addition, zerovalent silicon has a high capability in the removal of heavy metals. 83% of Cr(VI) was removed by 0.5g Si0 within 5 h, which is higher than that by Fe0. The removal efficiency of divalent metal ions by Si0 followed the order of Cu(II) > Pb(II) > Ni(II). This indicates that zerovalent silicon is an alternative reductant and can undergo coupled reduction of heavy metals and chlorinated hydrocarbons in contaminated groundwater.     

Reductive dechlorination of 1, 2-dichloroethane using anaerobic sequencing batch reactor (ASBR)

The objective of this research was to study the dechlorination of 1,2-dichloroethane (1,2-DCA) in a synthetic wastewater with lab-scale anaerobic sequencing batch (ASBR) reactors. Anaerobic sludge was used as a biocatalyst. Sodium acetate and dextrose served as the main methanogenic substrate. Experimental studies were conducted at wide-range of volumetric (0.25-1.25 g COD/L.d) and specific (0.0362-0.181 g COD/ g VSS.d) loading rates and influent wastewater CODs (500-2500 mg/L). During 266 days of reactor operation, the mixed culture degraded 1,2 dichloroethane at concentrations of up to 50 mg/L, with an HRT of 48 hrs. No chlorinated intermediates or residues were found. 1,2-DCA degradation resulted in ethene and ethane formation. Acetate was the most effective electron donor for dechlorination, although, dextrose was also effective, but to a lesser extent. The mixed culture degraded 1,2 Dichloroethane in the temperature range of 28+/-4 degrees C, with the pH range of 7.25 to 7.95. The 1,2-DCA removal rates achieved, and the safe nature of the end products, signify the anaerobic sequencing batch (ASBR) reactor technology for practical decontamination of waters containing such types of organochlorines. The COD removal efficiencies were in the range of 95 to 98% depending on volumetric and specific loading rates applied.     

Reduction of bromate in groundwater with an ex situ suspended growth bioreactor.

A potential remediation technique for groundwater contaminated by bromate has been investigated, utilising biological bromate reduction to bromide by augmentation of indigenous microbial populations. This technique, involving addition of a carbon source to contaminated groundwater, is being developed as an ex-situ methodology analogous to commercial denitrification systems, but may also have in-situ applications. Trials have focussed on a laboratory-scale anaerobic suspended growth chemostat system, investigating glucose addition to real groundwater supplies. Steady states for a range of glucose and bromate concentrations demonstrated bromate reduction up to 700 microgl(-1) (50% of 1400 microgl(-1) influent) with glucose excess (above 52 mgl(-1)), but specific reduction rates (up to 2.83 micromol Br.g dry wt(-1) hr(-1) for 1400 microgl(-1) bromate influent) were low compared to denitrification (up to 305 micromol N g dry wt(-1) hr(-1)). More recent enrichment trials have demonstrated reduction of 32 mgl(-1) bromate within a 40 hour residence time with specific reduction rates of up to 160.48 micromol Br.g dry wt(-1) hr(-1), suggesting the presence of high rate bromate reducing bacterial strains.     

Removal of arsenic from groundwater by arsenite-oxidizing bacteria

The presence of arsenic in groundwater has been of great public concern because of its high toxicity. For purification of arsenic-contaminated groundwater, bacterial oxidation of arsenite, As(III), with a chemical adsorption process was examined in this study. After As(III) oxidation to arsenate, As(V), arsenic is easily removable from contaminated groundwater because As(V) is more adsorptive to absorbents than As(III). By acclimation to As(III) of high concentrations, a mixed culture of heterotrophic bacteria with high As(III)-oxidizing activity was obtained from a soil sample that was free from contamination. With initial concentration up to 1,500 mg l(-1) As(III), the mixed culture showed high As(III)-oxidizing activity at pH values of 7-10 and at temperatures of 25-35 degrees C. The mixed culture contained several genera of heterotrophic As(III)-oxidizing and arsenic-tolerant bacteria: Haemophilus, Micrococcus, and Bacillus. Activated alumina was added to the basal salt medium containing 75 mg l(-1) As(III) before and after bacterial oxidation. Arsenic removal by activated alumina was greatly enhanced by bacterial oxidation of As(III) to As(V). The isotherms of As(III) and As(V) onto activated alumina verified that bacterial As(III) oxidation is a helpful pretreatment process for the conventional adsorption process for arsenic removal.     

Biodegradation of chlorobenzene in a constructed wetland treating contaminated groundwater.

Monochlorobenzene (MCB) is an important groundwater contaminant world-wide. In this study, a horizontal subsurface flow constructed wetland with an integrated water compartment was fed with MCB contaminated groundwater originating from the local aquifer. Analysis of spatial concentration dynamics of MCB and oxygen was combined with isotope composition analysis of MCB for assessing in situ biodegradation. Removal of MCB was most effective in the upper layer of the soil filter, reaching up to 77.1%. Trace oxygen concentrations below 0.16 mg L(-1) were observed throughout the wetland transect, suggesting a considerable limitation of aerobic microbial MCB degradation. Enrichment of 13C in the residual MCB fraction at increasing distance from the inflow point indicated microbial MCB degradation in the wetland. The observed isotope shift was higher than expected for aerobic MCB degradation and thus pointed out a significant contribution of an anaerobic degradation pathway to the overall biodegradation.     

The use of a mathematical model to evaluate mercury accumulation in sediments and recovery time in a coastal lagoon (Ria de Aveiro,Portugal)

The urge of restoration and management of vital ecosystems (mainly those that affect directly human health) has become one of the most requested priorities. Ria de Aveiro (a lagoon on the north-western coast of Portugal) has an important economic role in local and surrounding areas due to its variety of resources. Studies have shown that there is an effective risk of hindering traditional activities due to high levels of mercury. Mercury concentrations in 1985 ranged from 0.7 μg g⁻¹ to 850 μg g⁻¹ in surface sediments and concentrations up to 25 μg g⁻¹ fresh weight in fishes. A mathematical model (ECoS) was used to perform a simulation of mercury accumulation in surface sediments along the most contaminated channel from the beginning of the industrial discharges (in the 50's) until present days and recovery time for a zero mercury discharge from 1995 until 2045. The model shows that the amount of mercury in the surface sediments would decrease exponentially due to both deposition of mercury free particles and ressuspension of less and less contaminated particles. The model estimated levels actually measured along the channel and evaluated that, even after 40 years, mercury concentration would be approximately 50 μg g⁻¹ in the most contaminated section of that channel if the discharges were discontinued now.     

PCB Congeners and Dechlorination in Sediments of Upper Sheboygan River,Wisconsin

Nine hand-collected sediment cores were obtained for PCB concentration analysis and dating from the Upper Sheboygan River, Wisconsin, USA. The primary PCB Aroclors in the Upper Sheboygan River were 1248 (50%) and 1254 (50%). The total PCB concentrations in the sediments ranged from 0.1–104 ppm (based on dry weight). The PCB data obtained from the sampling were analyzed using a factor analysis (FA) model with non-negative constraints in order to identify PCB sources and congener patterns. The factor loadings obtained from the FA model represent a general dechlorination profile common to most of the higher concentration samples and another associated with contamination from upstream dredging during 1989–1991. Anaerobic dechlorination is occurring in Upper Sheboygan River sediments and is most significant at high concentrations (≥ 20 ppm). Observation of elevated amounts of lower chlorinated congeners such as congeners 4 (2-2), 8 (2-4), 25 (24-3), and 26 (25-3) indicates the presence of anaerobic dechlorination activities. Based on the data from the FA model, anaerobic dechlorination was occurring according to dechlorination activities M and P. All possible dechlorination pathways involving marker congeners were considered. A significant improvement (86–91%) in similarity between the original Aroclor profile and the altered ones was found.     

In situ source zone sediment mixing coupled to groundwater biostimulation to enhance phenol natural attenuation

Phenol is an industrially key compound that has a wide range of applications and also one of the most commonly found toxic pollutants in wastewaters and groundwater. This paper demonstrates the applicability of in situ remediation at a deactivated industrial site using source zone excavation and sediment mixing associated with nutrients delivery into groundwater. Sediment excavation and mixing displaced the entrapped source zone enhancing mass transfer into groundwater and contaminant bioavailability. A nutrient solution prepared with nitrate, phosphate, sodium hydroxide and hydrogen peroxide was continuously delivered into groundwater to stimulate biodegradation and restrict plume migration. The observed correlation between phenol-dependent Enterobacteriaceae concentrations throughout the remediation time frame supported circumstantial evidence of biodegradation. Phenol concentration in groundwater (up to 1,300 mg/L) was reduced >99% after 5 months following remediation and remained under the established site specific target level (4 mg/L). Nitrate and phosphate concentrations returned to background concentrations levels at the end of the remediation. Overall, the proposed in situ remediation scheme was effective to remediate this particular aquifer contaminated with phenol for over 20 years.     

基于特定污染场地的蒸汽入侵健康风险评估案例

对某汽车零部件厂搬迁后的场地环境调查结果显示, 该场地浅层地下水中存在氯乙烷、 1, 1 2二氯乙烯和 1, 12 二氯乙烷三种氯代烃污染, 且可能存在通过挥发进入室内对人体造成健康危害的风险。该场地浅层地下水平均水 位 0182 m, 地下室埋深3166 m, 地下水水位在地下室底板以上, 现有导则中基于地下室在地下水水位以上的蒸汽入 侵模型不适用于该场地。构建了适用于实际场地的地下室渗水蒸汽入侵模型, 并利用该模型和现有蒸汽入侵模型 分别进行了致癌健康风险评价, 完成了地下水污染物风险控制值计算。对比不同模型计算结果发现, 现有模型计算 所得的健康风险水平均比地下室渗水模型小 250 倍以上, 远远低估了健康风险。     

南水北调中线沿线劣质地下水对输水水质的潜在风险分析

确保南水北调中线工程供水水质安全是工程运行成功的关键。现通过对中线工程总干渠沿线地下水进入渠道可能性分析的基础上，建立典型渠段数值模型定量计算地下水与渠系水在水量与水质的转化。研究结果表明：工程内排排水的布设使地下水与渠系水存在水量与水质的紧密联系；地下水向渠道的排入量取决于地下水水位与总干渠渠道水位之间水位差的变化情况以及区域水文地质条件；根据现有资料基础上的河北磁县境内渠段模拟计算结果，即使在假定的污染风险达到极大的情况下，排入渠道的劣质地下水对渠系水水质基本不构成影响。     

Biological treatment of toluene contaminated wastewater by Alcaligenese faecalis in an extractive membrane bioreactor; experiments and modeling

Conventional wastewater treatment methods are not efficient in treating wastewaters contaminated with volatile hydrocarbons such as benzene, toluene and xylenes (BTX). The aim of this study is to enhance the efficiency of an extractive membrane bioreactor (EMBR) in treating toluene contaminated wastewater by usage of pure culture of Alcaligenese faecalis. Toluene was used as a model of toxic contaminant because of its wide presence in wastewaters contaminated with petrol derivatives. The Haldane kinetic model adequately described the dynamic behavior of the toluene biodegradation by the strain of A. faecalis over a wide range of initial toluene concentrations (50-1,000 mg L(-1)) with kinetic constants micro(max) = 0.066 h(-1), k(s) = 91.7 mg/L and k(I) = 278.2. Overall mass transfer coefficient has been measured and described as resistance in the series model. No biofilm formed on the exterior surface of the membrane; however in previous works the layer of the biofilm on the exterior surface of the membrane acts as a mass transfer resistance. A mathematical model was developed to predict the pollutant concentration profile along the tube side of the membrane modules.     

Runoff and windblown vehicle spray from road surfaces, risks and measures for soil and water.

Soil and surface water along roads are exposed to pollution from motorways. The main pollutants are polycyclic aromatic hydrocarbons (PAH), mineral oil, heavy metals and salt. These pollutants originate from vehicles (fuel, wires, leakage), wear and degradation of road surfaces and road furniture (i.e. crash barriers) and the application of de-icing salts. Runoff, vehicle spray and dry deposition disperse these contaminants into the soft shoulder (verges) of the roads and surface water to a measurable distance of about 50 up to more then 150 m from the road. Despite many monitoring programs, little is known about the risks of this diffuse pollution for soil and water quality and the geochemical and physical factors which determine these risks. Also little is known about the effects of possible measures. Therefore, extensive research has been carried out at two local motorways. Specific measurements on runoff, vehicle spray and effects of measures have been carried out for one year (13 months). This resulted in several new insights. The pollutants appear to adsorb effectively to natural soils. In vulnerable areas groundwater can be protected by adjusting the policy to removing the contaminated upper topsoil of the verges. Discharges of runoff into local surface water are not recommended.     

Characterization of microbial community structures and their activities in single anaerobic granules by beta imaging, microsensors and fluorescence in situ hybridization

The spatial distribution of microorganisms and their in situ activities in anaerobic granules were investigated by fluorescence in situ hybridization (FISH), beta imaging and microsensors. FISH results revealed a layered structure of microorganisms in the granule, where Chloroflexi was present in the outermost layer, Smithella spp. and Syntrophobacter spp. were found in a depth of ca. 100 μm, and Archaea was restricted to the inner layer (below ca. 300 μm from the surface). Substrate uptake patterns elucidated by beta imaging demonstrated that glucose uptake was highest at 50 μm depth, whereas propionate uptake had a peak at 200 μm depth. In addition, microsensor measurements revealed that acid was produced mainly at 100 μm depth and H(2) production was detected at a depth from 100 to 200 μm. H(2) consumption and corresponding CH(4) production were found below 200 μm from the surface. Direct comparison of these results implied sequential degradation of complex organic compounds in anaerobic granules; Chloroflexi contributed to fermentation of organic compounds and acid production in the outermost layer, volatile fatty acids were oxidized and H(2) was produced mainly by Smithella spp. and Syntrophobacter spp. at a depth from 100 to 200 μm, and Archaea produced CH(4) below ca. 300 μm from the surface.     

Absorption of Hydrophobic Contaminants from Ingested Chlamydomonas rheinhardtii and Chlorella vulgaris by Zebra Mussels,Dreissena polymorpha

The zebra mussel, Dreissena polymorpha, has the potential to influence contaminant cycling in freshwater systems because of its large population density, high lipid content, and high filtering rate. Ingestion of contaminated particles such as algae dominates exposure routes for the zebra mussel for strongly particle-associated contaminants. However, the data on absorption efficiency are limited and models to predict contaminant accumulation for the lower food web have identified the absence of such data as limiting and necessary to improve predictions. Accumulation of 2,2′,4,4′-tetrachlorobiphenyl (TCBP), 3,3′,4,4′,5-pentachlorobiphenyl (PCBP), 2,2′,4,4′,5,5′-hexachlorobiphenyl (HCBP) and 1,1- dichloro-2,2-bis[4-chlorophenyl] ethylene(DDE) was determined at two algal concentrations from exposures to contaminated Chlamydomonas rheinhardtii and Chlorella vulgaris. The contaminant absorption efficiencies were determined based on a chemical-mass-balance model. Mussel absorption efficiencies for the four chemicals at the two different algal concentrations for the two algal species ranged from 68.3% to 95.4% and were independent of algal concentrations and algal species for the same chemical.     

广西姚村地下河水化学特征及其时空变化

以广西黎塘姚村地下河为研究对象,通过对丰水期(6月份)、平水期(9月份)、枯水期(12月份)各采样点的地下水进行水化学研究,揭示了姚村地下河的水化学组成,探讨其水化学性质时空变化。结果表明:在空间上,电导率、Ca²⁺ 和Mg²⁺ 浓度自地下河上游至下游逐步升高,地下河出口处(3^#采样点)电导率远高于其他点(丰水期589 μS/cm、平水期634 μS/cm、枯水期614 μS/cm);在时间分布上,pH值,SO₄^2-,NO₃^-浓度季节变化明显,地下河出口处(3^#采样点)的NO₃^- 浓度在枯水期有明显升高;研究区地下水的化学性质受岩溶作用的强弱程度以及农业活动的影响。     

Sediment Contamination in the St. Lawrence River Along the Cornwall,Ontario Waterfront

Studies from 1970 to 1997 repeatedly showed that sediment was contaminated with mercury and zinc and, to a lesser extent, lead and copper in the north channel of the St. Lawrence River along the Cornwall, Ontario waterfront. Mercury contamination was greatest at two depositional zones: downstream of the Cornwall canal discharge near Lamoureux Park boat launch (maximum 18.0 μg/g, 1975) and downstream of Windmill Point (maximum 44.0 μg/g, 1975). Contaminant concentrations decreased with increasing distance from local point sources. The latter depositional zone extended approximately 2 km downstream and had the highest concentrations of mercury as well as high zinc, copper, and lead concentrations. Concentrations of As, Fe, Mn, Cd, Ni, Cr, TP, TKN, and TOC showed no significant local enrichment. Patterns of sediment contamination suggest local sources of PAHs; however, concentrations were not high enough to be of concern. The studies indicated that mercury and zinc were primarily from local industrial sources, a conclusion supported by patterns of contamination in the north versus south channels and downstream into Lake St. Francis. Although mercury concentrations in surface sediment appear to be decreasing over time, contaminants remain at high concentrations in Cornwall waterfront sediment. The two major local point sources of mercury closed their Cornwall industrial operations in the 1990s, but contaminated sediment can act as an important long-term source of mercury to the aquatic food chain. Conclusions drawn from this review will be used in the development of a strategy for managing contaminated sediment in Cornwall and may be applicable to other areas of contaminated sediment for which similar assessments are required.     

River, reservoir and lake sediment contamination by heavy metals downstream from urban areas of Switzerland

This paper quantifies sediment contamination by heavy metals in four reservoirs and one lake located downstream from major urban areas in Switzerland. The waterbodies include the Wettingen Reservoir (located on the Limmat River downstream from Zürich), the Klingnau Reservoir (on the lower Aare River), the Wohlen Reservoir (downstream from Berne), the Verbois Reservoir (downstream from Geneva) and Vidy Bay (Lake Geneva, city of Lausanne). For all sediment cores and contaminants, a trend is observed from high contaminant values in the lower part of the cores, decreasing to lower concentrations in the upper part of the cores. However, for each site and each element, specific features are recognized. Applying the criteria of the Swiss ordinance on soil protection, all sediment cores must be classified as contaminated by one or more contaminants and at variable levels. From these data, it is concluded that: reservoirs and lakes located downstream from major urban centres in Switzerland have accumulated significant volumes of contaminated sediments in the past, representing the largest, but not the most intensely, contaminated sites on a national scale; the main environmental risk is remobilization of the contaminants and their return to the food chain, particularly by infiltration into the groundwater; and although the processes of remobilization are identified, the conditions of occurrence and the amplitude of the processes are still poorly known. Different options of reservoir and lake sediment management also are discussed and further research topics defined.