Volatile Chlorinated Hydrocarbons Research Articles

Enhancement of gaseous chlorobenzene biodegradation and power generation in a microbial fuel cell by bifunctional Acinetobacter sp. HY-99C

The efficient biodegradation of volatile chlorinated hydrocarbons using microbial fuel cells (MFCs) offers a feasible approach for purifying waste gas and alleviating energy crises. However, power generation is limited by poor pollutant biodegradation and slow electron transfer. The bifunctional bacterium Acinetobacter sp. HY-99C was screened and used to improve the performance of a conventional MFC. The inoculation of strain HY-99C into the conventional MFC promoted the formation of a compact biofilm with high metabolic activity and an enriched bifunctional genus (Acinetobacter), which resulted in the accelerated decomposition of chlorinated aromatic compounds into biodegradable organic acids. This led to efficient chlorobenzene removal and power generation from the MFC, with a chlorobenzene elimination capacity of 70.8 g m−3 h−1 and power density of 89.6 mW m−2, which are improved over those of previously reported MFCs. This study provides novel insights into enhancing pollutant removal and power generation in MFCs.

Quantitative analysis of TCE biodegradation pathway in landfill cover utilizing continuous monitoring, droplet digital PCR and multi-omics sequencing technology

The remediation of volatile chlorinated hydrocarbons in the quasi-vadose zone has become a significant challenge. We applied an integrated approach to assess the biodegradability of trichloroethylene to identify the biotransformation mechanism. The formation of the functional zone biochemical layer was assessed by analyzing the distribution of landfill gas, physical and chemical properties of cover soil, spatial-temporal variations of micro-ecology, biodegradability of landfill cover soil and distributional difference metabolic pathway. Real-time online monitoring showed that trichloroethylene continuously undergoes anaerobic dichlorination and simultaneous aerobic/anaerobic conversion-aerobic co-metabolic degradation on the vertical gradient of the landfill cover system and reduction in trans-1,2-dichloroethylene in the anoxic zone but not 1,1-dichloroethylene. PCR and diversity sequencing revealed the abundance and spatial distribution of known dichlorination-related genes within the landfill cover, with 6.61 ± 0.25 × 104–6.78 ± 0.09 × 106 and 1.17 ± 0.78 × 103–7.82 ± 0.07 × 105 copies per g/soil of pmoA and tceA, respectively. In addition, dominant bacteria and diversity were significantly linked with physicochemical factors, and Mesorhizobium, Pseudoxanthomonas and Gemmatimonas were responsible for biodegradation in the aerobic, anoxic and anaerobic zones. Metagenome sequencing identified 6 degradation pathways of trichloroethylene that may occur in the landfill cover; the main pathway was incomplete dechlorination accompanied by cometabolic degradation. These results indicate that the anoxic zone is important for trichloroethylene degradation.

A starch-based controlled-release targeted nutrient agent to stimulate the activity of volatile chlorinated hydrocarbon-degrading indigenous microflora present in groundwater

Volatile chlorinated hydrocarbons (VCHs) contaminated groundwater has a low indigenous microorganism population, and lack of nutrient substrates involved in degradation reactions, resulting in a weak natural remediation ability of groundwater ecosystems. In this study, based on the principle of degradation of VCHs by indigenous microorganisms in groundwater, and combined with biostimulation and controlled-release technology, we developed a starch-based encapsulated targeted bionutrient (YH-1) with easy uptake, good stability, controllable slow-release migration, and long timeliness for the remediation of groundwater contaminated by VCHs by indigenous microorganisms. The results showed that YH-1 is easily absorbed by microorganisms and can rapidly initiate itself to stimulate the microbial degradation of VCHs, and the degradation rate of various VCH components within 7 days was 82.38–92.38 %. The release rate of nutrient components in YH-1 increases with increasing VCH concentrations in groundwater; this could effectively prolong the action time of nutrient components, while also improving the degradation efficiency of pollutants with a sustained effect of more than 15 days. Simultaneously, owing to the fluidity, water solubility, and biodegradability of YH-1 in lithologic media, YH-1 injection did not cause blockage of the lithologic media in the aquifer. Through YH-1 stimulation, indigenous microorganisms grew rapidly in the underground environment, the diversity of microbial communities and the total number of species increased, and the correlation between genera strengthened. Simultaneously, YH-1 improved the ability of microbial community to convert inorganic electron donors/acceptors, thereby strengthening the co-metabolic mechanism between microorganisms. Additionally, there was a significant increase in the percentage of many microorganisms (e.g., Sphingomonas, Janthinobacterium, Duganella, etc.) that mediated the reductive dechlorination process and were redox inorganic electron donors/acceptors. This was conducive to the reductive dechlorination process of VCHs and achieved the efficient degradation of VCHs.

Needle extraction device for rapid and quantitative gas chromatographic determination of volatile chlorinated hydrocarbons and benzene in soil

A rapid and quantitative analytical method for volatile chlorinated hydrocarbons and benzene, such as chloroethylene, dichloromethane, and carbon tetrachloride, in soil samples was developed using a needle-type extraction device packed with activated carbon-based adsorbents. The soil sample of 10 g was placed in a glass cartridge and fixed with quartz wool to make sure not to move during the extraction process. After the internal standard solution was spiked into the soil sample, the cartridge was sealed with a polytetrafluoroethylene adapter, and the needle extraction device was used to collect the headspace gas. Analytes were purged from the soil sample and collected on the adsorbent, while pure nitrogen gas was introduced to the soil sample during the sample collection. The sampling time was approximately 10 min for 100 mL of gas sampling. After the sampling process, the extraction needle was directly inserted into a heated injection port of gas chromatography equipped with flame ionization detector (GC-FID) or that hyphenated to mass spectrometry (GC–MS). The extracted VOCs were thermally desorbed and simultaneously introduced to a GC capillary column for subsequent separation and determination. The limit of detection and limit of quantification of all the examined analytes was less than 20 and 60 ng/10 g soil in GC-FID and less than 2.5 and 7.5 ng/10 g soil in the case of GC–MS. Linear calibration curves were obtained up to 10 μg/10 g soil for all the analytes. The relative standard deviations of the ratio of analyte peak area and internal standard peak area were less than 10%. The recovery and sensitivity of analytes confirmed in the proposed method were compared with that obtained with a standard method conventionally employed.

Influence of nitrate concentration on trichloroethylene reductive dechlorination in weak electric stimulation system

The co-existence of volatile chlorinated hydrocarbons (VCHs) and nitrate pollution in groundwater is prominent, but how nitrate exposure affects weak-electrical stimulated bio-dechlorination activity of VCH is largely unknown. Here, by establishing weak-electrical stimulated trichloroethylene (TCE) dechlorination systems, the influence on TCE dechlorination by exposure to the different concentrations (25–100 mg L−1) of nitrate was investigated. The existence of nitrate in general decreased TCE dechlorination efficiency to varying degrees, and the higher nitrate concentration, the stronger the inhibitory effects, verified by the gradually decreased transcription levels of tceA. Although the TCE dechlorination kinetic rate constant decreased by 36% the most, under all nitrate concentration ranges, TCE could be completely removed within 32 h and no difference in generated metabolites was found, revealing the well-maintained dechlorination activity. This was due to the quickly enriched bio-denitrification activity, which removed nitrate completely within 9 h, and thus relieved the inhibition on TCE dechlorination. The obvious bacterial community structure succession was also observed, from dominating with dechlorination genera (e.g., Acetobacterium, Eubacterium) to dominating with both dechlorination and denitrification genera (e.g., Acidovorax and Brachymonas). The study proposed the great potential for the in situ simultaneous denitrification and dehalogenation in groundwater contaminated with both nitrate and VCHs.

Application Case of Accurate Site Investigation with Life-Cycle Conceptual Site Model Development

A life cycle conceptual site model (LC-CSM) can represent the actual spatial distribution and migration of pollution of a site very accurately and be beneficial in supporting decisions for accurate site remediation or risk management. A volatile chlorinated hydrocarbon contaminated site in the Beijing-Tianjin-Hebei region was chosen as the study case. LC-CSMs were established following the site assessment, preliminary investigation, detailed investigation, and supplementary investigation of each stage. The application of field screening tests such as a membrane interface probe and the multi-electrode resistivity method assisted in identifying potential pollution sources and hot points. Concurrently, a large amount of vinyl chloride, the end product of chlorinated hydrocarbon degradation, was detected in some boreholes, indicating that pollutant biodegradation had occurred at this site. Some typical boreholes and cross-sections were chosen to analyze the biodegradation indicators and chemical fingerprints, combining the results of the comprehensive score of chlorinated hydrocarbon anaerobic biodegradability in groundwater reaching 22. It is judged that the site has strong anaerobic biodegradability. This step-by-step optimization forms an LC-CSM for site investigation, which provides scientific support for accurate site characterization.

Development of VCHs Transfer Mechanism and Remediation Technology in Contaminated Sites

In recent years, with the adjustment of China’s economic structure and the acceleration of urbanization, a large number of heavily polluting enterprises are facing shutdown and relocation, the residual volatile chlorinated hydrocarbons (VCHs) in the site become the priority pollutants in soil and groundwater due to the great threat to human body and environment. How to accurately predict the occurrence state and pollution degree of VCHs in the polluted site and put forward reasonable and targeted effective prevention and control strategy has become an international problem to be solved. The remediation technology of volatile chlorinated hydrocarbons (VCHs) in contaminated sites is introduced systematically, which will provide scientific basis for the practical remediation of contaminated sites in the future.

Comparison of the health risks associated with different exposure pathways of multiple volatile chlorinated hydrocarbons in contaminated drinking groundwater

A total of 152 groundwater samples were collected around a contaminated site to evaluate the carcinogenic and noncarcinogenic risks of exposure to twelve volatile chlorinated hydrocarbons (VCHs) by oral ingestion, dermal contact and inhalation absorption during showering. Although toxicity data of some VCHs are fragmentary, the results showed that the carcinogenic and noncarcinogenic risks of exposure to VCHs in contaminated drinking groundwater for local residents needs immediate attention. The main risk contributors for the carcinogenic and noncarcinogenic risks are carbon tetrachloride and 1,1,2-trichloroethane through inhalation exposure pathway, respectively. The health risk contribution rates associated with three exposure pathways for a specific VCH were intrinsic to the compound, and the dermal contact corresponded to a negligible contribution for almost every VCH species. Although most of the evaluated VCHs had a higher risk contribution by inhalation than by oral ingestion pathway, the integrated multi-VCH health risk contributions of the three exposure pathways were mainly dependent on the VCH compositions. Drinking boiled water not only decreased the exposure risk but also affected the risk contribution rates of three exposure pathways, which indicates that it is feasible to reduce the risk of VCH exposure during daily activities based on the risk contribution of the exposure pathways. In addition to the VCHs included in the drinking water standards, species such as 1,1,2,2-tetrachloroethane and hexachloroethane also showed a remarkable exposure health risk according to the standardized health risk calculation, which implied that improved drinking water standards are urgently required.

Bioelectrochemical assisted dechlorination of tetrachloroethylene and 1,2-dichloroethane by acclimation of anaerobic sludge

Volatile chlorinated hydrocarbons (VCHs) are often found as a type of persistent and ubiquitous contaminant in groundwater. The feasibility, characteristics and microbial mechanism of acclimation of biodiversity-rich inoculation source for bioelectrochemical stimulated VCH dechlorination remain poorly understood. Here, the superior bioelectrochemical catalytic activities were observed for tetrachloroethylene (0.26 mM d−1) and 1,2-dichloroethane (2.20 mM d−1) dechlorination in anaerobic sludge-acclimated biocathodes with an optimal potential of −0.5 V, averaging 1.60–2.71 times higher than those reported in previous works on biocathodes. When the cathode was applied as the sole electron donor for dechlorination, columbic efficiencies reached the values greater than 80%. Tetrachloroethylene dechlorination showed a metabolic pathway with cis-1,2-dichloroethene as the main product, whereas 1,2-dichloroethane was dechlorinated entirely to the nontoxic ethene. The cathodic biofilms were highly abundant with the dechlorination and electro-active genera, while significant bacterial consortium variation was observed in response to the different VCH types and changes in cathodic potential. Bacillus, Pseudomonas and Lactococcus were mostly enriched for tetrachloroethylene dechlorination, and pceA, tceA and omcX were highly expressed. Geobacter was the most predominant during 1,2-dichloroethane dechlorination with rdhA, tceA and omcX highly expressed. In addition, although the impact of cathodic potentials was weaker than that of VCH types, the lower cathodic potentials, the more abundant of the electrode respiring populations and the higher expression of extracellular electron transfer related gene. This study demonstrated the great potential of acclimation of anaerobic sludge by electrical stimulation for accelerating VCH remediations and gave insights into its working molecular mechanisms.

1,4-Dioxane pollution at contaminated groundwater sites in western Germany and its distribution within a TCE plume

An effective and sensitive method for the analysis of 1,4-dioxane in water has been available since 2008 (EPA 522). This method is increasingly being applied to investigate the distribution of 1,4-dioxane in the aquatic environment. However, there is a need for more information about the possible occurrence of 1,4-dioxane in groundwater in Europe in general, and in Germany in particular, where virtually no data have been collected so far. The possible contamination of groundwater with 1,4-dioxane is of relevance to Germany because up to 70% of Germany's drinking water is obtained from groundwater and about 17% from river bank filtrate, which contains variable proportions of groundwater. The aim of the present study is to investigate selected and representative groundwater sites in Germany that have suspected occurrences of 1,4-dioxane. Five of the sites are well known for their volatile chlorinated hydrocarbon contamination, two sites have representative landfill leachate characteristics, and one site is negatively impacted by a detergent manufacturing plant. The presence of 1,4-dioxane was observed at each of these sites. Measured maximum concentration values ranged from 0.15μg/L to 152μg/L. An aquifer containing a trichloroethylene (TCE) plume with 1,4-dioxane as a co-contaminant was investigated in more detail. A perfect match was found between the concentrations of 1,4-dioxane and TCE in the vertical and horizontal distribution profiles. The results indicate the necessity for investigating groundwater contamination by 1,4-dioxane at sites with known 1,1,1-trichloroethane (TCA) and TCE contaminations, in landfill leachates, and at sites of detergent production.

Quicklime-induced changes of soil properties: Implications for enhanced remediation of volatile chlorinated hydrocarbon contaminated soils via mechanical soil aeration

Mechanical soil aeration is used for soil remediation at sites contaminated by volatile organic compounds. However, the effectiveness of the method is limited by low soil temperature, high soil moisture, and high soil viscosity. Combined with mechanical soil aeration, quicklime has a practical application value related to reinforcement remediation and to its action in the remediation of soil contaminated with volatile organic compounds. In this study, the target pollutant was trichloroethylene, which is a volatile chlorinated hydrocarbon pollutant commonly found in contaminated soils. A restoration experiment was carried out, using a set of mechanical soil-aeration simulation tests, by adding quicklime (mass ratios of 3, 10, and 20%) to the contaminated soil. The results clearly indicate that quicklime changed the physical properties of the soil, which affected the environmental behaviour of trichloroethylene in the soil. The addition of CaO increased soil temperature and reduced soil moisture to improve the mass transfer of trichloroethylene. In addition, it improved the macroporous cumulative pore volume and average pore size, which increased soil permeability. As soil pH increased, the clay mineral content in the soils decreased, the cation exchange capacity and the redox potential decreased, and the removal of trichloroethylene from the soil was enhanced to a certain extent. After the addition of quicklime, the functional group COO of soil organic matter could interact with calcium ions, which increased soil polarity and promoted the removal of trichloroethylene.

Treatability of volatile chlorinated hydrocarbon-contaminated soils of different textures along a vertical profile by mechanical soil aeration: A laboratory test

Mechanical soil aeration is a simple, effective, and low-cost soil remediation technology that is suitable for sites contaminated with volatile chlorinated hydrocarbons (VCHs). Conventionally, this technique is used to treat the mixed soil of a site without considering the diversity and treatability of different soils within the site. A laboratory test was conducted to evaluate the effectiveness of mechanical soil aeration for remediating soils of different textures (silty, clayey, and sandy soils) along a vertical profile at an abandoned chloro-alkali chemical site in China. The collected soils were artificially contaminated with chloroform (TCM) and trichloroethylene (TCE). Mechanical soil aeration was effective for remediating VCHs (removal efficiency >98%). The volatilization process was described by an exponential kinetic function. In the early stage of treatment (0–7hr), rapid contaminant volatilization followed a pseudo-first order kinetic model. VCH concentrations decreased to low levels and showed a tailing phenomenon with very slow contaminant release after 8hr. Compared with silty and sandy soils, clayey soil has high organic-matter content, a large specific surface area, a high clay fraction, and a complex pore structure. These characteristics substantially influenced the removal process, making it less efficient, more time consuming, and consequently more expensive. Our findings provide a potential basis for optimizing soil remediation strategy in a cost-effective manner.

Analysis of chlorinated hydrocarbons in gas phase using a portable membrane inlet mass spectrometer

A compact portable membrane inlet mass spectrometer (MIMS) has been used for the first time to detect and monitor, both qualitatively and quantitatively, volatile chlorinated hydrocarbons in the gaseous phase.

Determination of volatile chlorinated hydrocarbons in water samples by static headspace gas chromatography with electron capture detection.

A simple, efficient, solvent-free, and commercial readily available approach for determination of five volatile chlorinated hydrocarbons in water samples using the static headspace sampling and gas chromatography with electron capture detection has been described. The proposed static headspace sampling method was initially optimized and the optimum experimental conditions found were 10 mL water sample containing 20% w/v sodium chloride placed in a 20 mL vial and stirred at 50ºC for 20 min. The linearity of the method was in the range of 1.2-240 μg/L for dichloromethane, 0.2-40 μg/L for trichloromethane, 0.005-1 μg/L for perchloromethane, 0.025-5 μg/L for trichloroethylene, and 0.01-2 μg/L for perchloroethylene, with coefficients of determination ranging between 0.9979 and 0.9990. The limits of detection were in the low μg/L level, ranging between 0.001 and 0.3 μg/L. The relative recoveries of spiked five volatile chlorinated hydrocarbons with external calibration method at different concentration levels in pure, tap, sea water of Jiaojiang Estuary, and sea water of waters of Xiaomendao were in the range of 91-116, 96-105, 86-112, and 80-111%, respectively, and with relative standard deviations of 1.9-3.6, 2.3-3.5, 1.5-2.7, and 2.3-3.7% (n = 5), respectively. The performance of the proposed method was compared with traditional liquid-liquid extraction on the real water samples (i.e., pure, tap, and sea water, etc.) and comparable efficiencies were obtained. It is concluded that this method can be successfully applied for the determination of volatile chlorinated hydrocarbons in different water samples.

Effect of Soil Water Content on the Removal of Volatile Chlorinated Hydrocarbons from Soil by Mechanical Soil Aeration

Mechanical soil aeration is an easy, effective, and low-cost soil remediation technology; in particular, it is suitable for large sites contaminated by volatile chlorinated hydrocarbons (VCHs). Mechanical soil aeration encourages the volatilization of soil contaminants, but soil moisture, which reduces the amount of open pores, may hinder this process. The present study examined the remediation of silty soil containing 1,2-dichloroethane (1,2-DCA), chloroform (TCM), trichloroethylene (TCE), and tetrachloroethylene (PCE) using mechanical soil aeration and evaluated the influence of soil water content on the efficiency of the process. For artificially contaminated soil, the following conclusions were reached: (i) moisture undermines the volatilization of contaminants. When the soil water content increased from 5% to 20%, the residual concentrations of 1,2-DCA, TCM, TCE, and PCE in the soil increased from 0.08, 0.10, 0.09, and 0.48 mg/kg to 1.43, 0.81, 1.16, and 1.43 mg/kg, respectively. The effective diffusion coefficients also decreased from 1.88×10-2, 1.43×10-2, 1.88×10-2, and 1.30×10-2 cm2/s to 1.71×10-6, 1.30×10-6, 1.71×10-6, and 1.18×10-6 cm2/s, respectively. (ii) Residual contaminants are related to the octanol-water partition coefficient. The soil-water distribution coefficient of PCE was highest among the hydrocarbons (3.72), and the residual contaminants were mainly adsorbed on soil particles. The soil-water distribution coefficient of DCA was lowest (0.42), and the residual contaminants were mainly dissolved in the soil water.

Low-concentration tailing and subsequent quicklime-enhanced remediation of volatile chlorinated hydrocarbon-contaminated soils by mechanical soil aeration

Mechanical soil aeration has long been regarded as an effective ex-situ remediation technique and as suitable for remediation of large-scale sites contaminated by volatile organic compounds (VOCs) at low cost. However, it has been reported that the removal efficiency of VOCs from soil is relatively low in the late stages of remediation, in association with tailing. Tailing may extend the remediation time required; moreover, it typically results in the presence of contaminants residues at levels far exceeding regulations. In this context, the present study aimed to discuss the tailing that occurs during the process of remediation of soils contaminated artificially with volatile chlorinated hydrocarbons (VCHs) and to assess possible quicklime-enhanced removal mechanisms. The results revealed the following conclusions. First, temperature and aeration rate can be important controls on both the timing of appearance of tailing and the levels of residual contaminants. Furthermore, the addition of quicklime to soil during tailing can reduce the residual concentrations rapidly to below the remedial target values required for site remediation. Finally, mechanical soil aeration can be enhanced using quicklime, which can improve the volatilization of VCHs via increasing soil temperature, reducing soil moisture, and enhancing soil permeability. Our findings give a basic understanding to the elimination of the tailing in the application of mechanical soil aeration, particularly for VOCs-contaminated soils.

Trends of volatile chlorinated hydrocarbons and trihalomethanes in Antarctica

In order to understand behaviour and environmental fate of manmade chemicals in remote and cold areas, during the XXVII Italian Expedition carried out in Antarctica throughout the austral summer 2011/2012, superficial snow and lake water were sampled along the Ross Sea's South coast and their content of some low-molecular weight volatile halogenated hydrocarbons was evaluated. In consideration of their important role in stratospheric ozone chemistry, some volatile chlorinated hydrocarbons (VCHCs) and trihalomethanes (THMs) were investigated. The analyses were realised with a dedicated system composed by a purge-and-trap injector coupled to a gas chromatograph with a mass spectrometer (PTI-GC-MS) operating in SIM mode. The investigated VCHCs (chloroform; 1,1,1-trichloroethane; tetrachloromethane; trichloroethylene and tetrachloroethylene) were present in all analysed samples, and concentration levels ranged from units to hundreds of ng L−1 according to considered matrix. For the first time, THMs (bromoform; dibromochloromethane; bromodichloromethane), were measured in Antarctic lake waters and freshly deposited snow; their concentration levels ranged from units to tens of ng L−1. In order to assess eventual temporal variations, VCHC content in aqueous Antarctic matrices was compared with levels occurring in the past Italian Antarctic expeditions: for some banned substances, a decrease in concentration was observed, probably due to worldwide use restrictions. Finally, current Antarctic and Italian VCHC and THM levels in snow and lake water samples were compared and were found to be quite similar, differing at most by one order of magnitude, corroborating the hypothesis of an accumulation of halogenated compounds in Antarctic aqueous matrices.

Removal of hazardous chlorinated VOCs from aqueous solutions using novel ZSM-5 loaded PDMS/PVDF composite membrane consisting of three hydrophobic layers

Hydrophobic polymer possesses significant potential for selective separation of volatile organic compounds (VOCs) from their aqueous solutions by pervaporation (PV). In the present study mixed matrix hydrophobic membranes of polydimethylsiloxane (PDMS) supported on polyvinylidenefluoride (PVDF) substrate were synthesized by incorporating hydrophobic inorganic ZSM-5 filler. The indigenous membranes were crosslinked with tetraethylorthosilicate (TEOS) for the extraction of volatile chlorinated hydrocarbons such as dichloromethane (DCM), trichloromethane (TCM), 1,2-dichloroethane (DCE), and 1,1,2,2-tetrachloroethane (TeCE), which pose serious environment threat and health hazard. Thermal stability, crosslinking, crystallinity, surface morphology and swelling characteristics of the indigenously developed membranes were determined by TGA, FTIR, XRD, SEM and sorption studies, respectively. Effect of operating parameters such as feed composition and filler concentration on separation performance in terms of flux and selectivity were determined. Flux of DCM, TCM, DCE and TeCE was found to be 0.166, 0.146, 0.141 and 0.06kgm−2h−1 with selectivity of 541, 1068, 917 and 15,000, respectively, for 20% ZSM-5 filled PDMS membrane for aqueous feeds containing 1.33% (w/v) DCM, 0.8% (w/v) TCM, 0.84% (w/v) DCE and 0.28% (w/v) TeCE in water. The membrane exhibited considerable feasibility for scale-up with significant potential for removal of hazardous chlorinated VOCs from aqueous solutions.

(Bio-)remediation of VCHC contaminants in a Technosol under unsaturated conditions

The remediation of dense non-aqueous phase liquids has always been a concern of both public and scientific interest groups. In this research work a modified physical concept of (bio)remediation of a volatile chlorinated hydrocarbon (VCHC) contamination was elaborated under laboratory conditions and modeled with HYDRUS-2D. In field dechlorination is influenced by both physicochemical and hydraulic properties of the substrate, e.g. texture, pore size distribution, pore liquid characteristics, e.g. viscosity, pH, surface tension, and dependent on the degree of saturation of the vadose zone. Undisturbed soil cores (100cm³) were sampled from a Spolic Technosol. Considering hydraulic properties and functions, unsaturated percolation was performed with vertically and horizontally structured samples. VCHC concentrations were calculated prior, during, and after each percolation cycle. According to laboratory findings, microemulsion showed the most efficient results with regard to flow behavior in the unsaturated porous media and its accessibility for bacteria as nutrient. The efficiency of VCHC remediation could be increased by the application of a modified pump-and-treat system: the injection of bacteria Dehalococcoides ethanogenes with microemulsion, and extraction at a constant matric potential level of -6kPa. Achieved data was used for HYDRUS-2D simulations, modeling in situ conditions, demonstrating the practical relevance (field scale) of performed unsaturated percolation (core scale), and in order to exclude capillary barrier effects.

Quantifying reduction in ecological risk in Penrhyn Estuary, Sydney, Australia, following groundwater remediation

The environmental risk associated with discharge of contaminated groundwater containing a complex mixture of at least 14 volatile chlorinated hydrocarbons (VCHs) to Penrhyn Estuary, Sydney, Australia has previously been assessed. That probabilistic ecological risk assessment (ERA) was undertaken using surface water monitoring data from 2004 to 2005. Subsequently, in 2006, a groundwater remediation system was installed and commissioned to prevent further discharge of VCHs into the estuary. The present study assessed the ecological risk posed to the estuary after 2006 to evaluate the success of the remediation system. The ERA was undertaken using toxicity data derived from direct toxicity assessment (DTA) of preremediation contaminated groundwater using indigenous species, exposure data from surface water monitoring between 2007 and 2008 and the joint probability curve (JPC) methodology. The risk posed was measured in 4 zones of the entire site: source area (2), tributary (2), the inner estuary and outer estuary at high, low, and a combination of high and low tides. In the 2 source areas, risk decreased by over 2 and over 1 orders of magnitude to maximum values of less than 0.5%. In 1 estuary, risk decreased by over 1 order of magnitude, from a maximum of 36% to a maximum of 2.3%. At the other tributary and both the inner and outer estuaries, the risk decreased to less than 1%, regardless of the tide. This analysis revealed that the remediation system was very effective and that the standard level of protection required for slightly to moderately affected ecosystems (95% of species) by the Australian and New Zealand Guidelines for Fresh and Marine Water Quality was met postremediation.