Bioremediation of TCE in a fractured limestone aquifer using a novel horizontal passive biobarrier

This article discusses a project demonstrating the successful use of a novel horizontal biobarrier approach to protect a fractured limestone aquifer from continuing contamination while passive bioremediation of the overlying clay till source area is in progress. The emplacement of the biobarrier has significantly reduced the concentrations of chlorinated ethenes and dechlorination activity in the limestone aquifer, promoting complete reductive dechlorination of the trichloroethene plume. The biobarrier strategy has thus met the challenge of protecting the limestone from the overlying overburden. Direct GeoProbe injections performed in the source area, which consist of a clay till overburden, have also reduced the contaminant concentrations in the clay till due to enhanced dechlorination activity; however, repeat injections may be required to address the areas of the till in which the injectate has not yet been distributed. The time frame for remediating the source area in the till is expected to be on the order of a decade. © 2010 Wiley Periodicals, Inc.     

The toxicity of composted sediments from Mediterranean ports evaluated by several bioassays

This work investigates the ecotoxicological evaluation of contaminated dredged sediments from French Mediterranean navy harbour (A), commercial port (B) and two composite specimens (C) and (D) coming from the mixture of A and B with other port sediments. The toxicity of elutriates from these sediments is estimated using embryo-toxicity test, Microtox® solid phase test, LuminoTox, phytotoxicity tests and genotoxicity test. Bioassay responses are not clearly correlated with chemical contamination in the whole sediment and vary as a function of tested organisms. The highest contaminated samples (A and C) are almost always more toxic than the less contaminated samples (B and D). Among composite sediments, the mixture effect with other sediments is not efficient to decrease toxicity in sample C, suggesting that other parameters influence toxicity level such as particle size or organic matter content. These parameters should be taken into consideration in order to improve the efficiency of the mixture process and produce composite sediments with low toxicity.     

Gas production, composition and emission at a modern disposal site receiving waste with a low-organic content

AV Miljø is a modern waste disposal site receiving non-combustible waste with a low-organic content. The objective of the current project was to determine the gas generation, composition, emission, and oxidation in top covers on selected waste cells as well as the total methane (CH₄) emission from the disposal site. The investigations focused particularly on three waste disposal cells containing shredder waste (cell 1.5.1), mixed industrial waste (cell 2.2.2), and mixed combustible waste (cell 1.3). Laboratory waste incubation experiments as well as gas modeling showed that significant gas generation was occurring in all three cells. Field analysis showed that the gas generated in the cell with mixed combustible waste consisted of mainly CH₄ (70%) and carbon dioxide (CO₂) (29%) whereas the gas generated within the shredder waste, primarily consisted of CH₄ (27%) and nitrogen (N₂) (71%), containing no CO₂. The results indicated that the gas composition in the shredder waste was governed by chemical reactions as well as microbial reactions. CH₄ mass balances from three individual waste cells showed that a significant part (between 15% and 67%) of the CH₄ generated in cell 1.3 and 2.2.2 was emitted through leachate collection wells, as a result of the relatively impermeable covers in place at these two cells preventing vertical migration of the gas. At cell 1.5.1, which is un-covered, the CH₄ emission through the leachate system was low due to the high gas permeability of the shredder waste. Instead the gas was emitted through the waste resulting in some hotspot observations on the shredder surface with higher emission rates. The remaining gas that was not emitted through surfaces or the leachate collection system could potentially be oxidized as the measured oxidation capacity exceeded the potential emission rate. The whole CH₄ emission from the disposal site was found to be 820 ± 202 kg CH₄ d⁻¹. The total emission rate through the leachate collection system at AV Miljø was found to be 211 kg CH₄ d⁻¹. This showed that approximately ¼ of the emitted gas was emitted through the leachate collections system making the leachate collection system an important source controlling the overall gas migration from the site. The emission pathway for the remaining part of the gas was more uncertain, but emission from open cells where waste is being disposed of or being excavated for incineration, or from horizontal leachate drainage pipes placed in permeable gravel layers in the bottom of empty cells was likely.     

Batch and column studies of the stabilization of toxic heavy metals in dredged marine sediments by hematite after bioremediation

The management of dredged sediments is an important issue in coastal regions where the marine sediments are highly polluted by metals and organic pollutants. In this paper, mineral-based amendments (hematite, zero-valent iron and zeolite) were used to stabilize metallic pollutants (As, Cd, Cu, Mo, Ni, Pb, and Zn) in a contaminated marine sediment sample. Mineral-based amendments were tested at three application rates (5 %, 10 %, and 15 %) in batch experiments in order to select the best amendment to perform column experiments. Batch tests have shown that hematite was the most efficient amendment to stabilize inorganic pollutants (As, Cd, Cu, Mo, Ni, Pb, and Zn) in the studied sediment. Based on batch tests, hematite was used at one application rate equal to 5 % to conduct column experiments. Column tests confirmed that hematite was able to decrease metal concentrations in leachates from stabilized sediment. The stabilization rates were particularly high for Cd (67 %), Mo (80 %), and Pb (90 %). The Microtox solid phase test showed that hematite could decrease significantly the toxicity of stabilized sediment. Based on batch and column experiments, it emerged that hematite could be a suitable adsorbent to stabilize metals in dredged marine sediment.     

Spatial Variability of Different Fractions of Particulate Matter within an Urban Environment and between Urban and Rural Sites

ABSTRACT

The spatial variability of different fractions of particulate matter (PM) was investigated in the city of Basel, Switzerland, based on measurements performed throughout 1997 with a mobile monitoring station at six sites and permanently recorded measurements from a fixed site. Additionally, PM₁₀ measurements from the following year, which were concurrently recorded at two urban and two rural sites, were compared.

Generally, the spatial variability of PM₄, PM₁₀, and total suspended particulates (TSP) within this Swiss urban environment (area = 36 km²) was rather limited. With the exception of one site in a street canyon next to a traffic light, traffic density had only a weak tendency to increase the levels of PM. Mean PM₁₀ concentration at six sites with different traffic densities was in the range of less than ±10% of the mean urban PM₁₀ level. However, comparing the mean PM levels on workdays to that on weekends indicated that the impact of human activities, including traffic, on ambient PM levels may be considerable.

Differences in the daily PM₁₀ concentrations between urban and more elevated rural sites were strongly influenced by the stability of the atmosphere. In summer, when no persistent surface inversions exist, differences between urban and rural sites were rather small. It can therefore be concluded that spatial variability of annual mean PM concentration between urban and rural sites in the Basel area may more likely be caused by varying altitude than by distance to the city center.     

Biodegradation of Trace Gases in Simulated Landfill Soil

Abstract

The attenuation of methane and seven volatile organic compounds (VOCs) was investigated in a dynamic methane and oxygen counter gradient system simulating a landfill soil cover. The VOCs investigated were: Tetrachloromethane (TeCM), trichloromethane (TCM), dichloromethane (DCM), trichloroethylene (TCE), vinyl chlo-ride (VC), benzene, and toluene. Soil was sampled at Skellingsted landfill, Denmark. The soil columns showed a high capacity for methane oxidation, with oxidation rates up to 184 g/m²/d corresponding to a 77% reduction of inlet methane. Maximal methane oxidation occurred at 15–20 cm depth, in the upper part of the column where there were overlapping gradients of methane and oxygen. All the chlorinated hydrocarbons were degraded in the active soil columns with removal efficiencies higher than 57%. Soil gas concentration profiles indicated that the removal of the fully chlorinated compound TeCM was because of anaerobic degradation, whereas the degradation of lower chlorinated compounds like VC and DCM was located in the upper oxic part of the column. Benzene and toluene were also removed in the active column. This study demonstrates the complexity of landfill soil cover systems and shows that both anaerobic and aerobic bacteria may play an important role in reducing the emission of trace components into the atmosphere.     

Economic incentives drive the conversion of agriculture to aquaculture in the Indian Sundarbans: Livelihood and environmental implications of different aquaculture types

Expansion of aquaculture in the Sundarbans Biosphere Reserve (SBR) is irreversibly replacing agricultural land and the drivers of this change are disputed. Based on in-depth interviews with 67 aquaculture farmers, this paper characterizes major aquaculture types in the SBR, their impacts, and identifies drivers of conversion from agricultural land. Aquaculture types included traditional, improved-traditional, modified-extensive, and semi-intensive systems. Extensive capture of wild shrimp larvae is environmentally harmful but constitutes an important livelihood. Semi-intensive aquaculture of exotic shrimp (Litopenaeus vannamei) has much higher unit-area profitability than other types but involves greater financial risk. Profitability is the main driver for the transition from agriculture, but environmental factors such as lowered crop yields and cyclone impacts also contributed. Many conversions from agriculture to aquaculture are illegal according to the stakeholders. Existing legislation, if enforced, could halt the loss of agriculture, while the promotion of improved-traditional aquaculture could reduce the demand for wild seed.     

Air pollution and diseases of the respiratory tracts in pre-school children: A transfer function model

The purpose of the present statistical analysis was the assessment of the relation between time series of environmental factors and of frequencies of diseases of the respiratory system in pre-school children. During about one year, daily measurements of air pollutants and climatic variables were taken. During the same period of time two series of medical data were collected: (i) The daily relative number of pre-school children, exhibiting diseases of the respiratory tracts who either came to the outpatients' clinic of the children's hospital or were reported by paediatricians in Basle (ENTRIES). (ii) The daily relative frequency of symptoms of the respiratory tracts observed in a group of randomly selected pre-school children (SYMPTOMS).By means of transfer function models the relation between the two target variables and the explaining variables was analysed. Several practical problems did arise: Choice of the appropriate transformation of the different series, interpretation of the crosscorrelation function using different methods of prewhitening, time splitting and nonstationarity of the crosscorrelation structure. In particular, it was found that after prewhitening the crosscorrelation function between the explanatory series SO₂ and the response series SYMPTOMS changes with time. While during the winter period an instantaneous relation between these two series (and to a lesser extent between NO₂ and SYMPTOMS) was identified, no such relation was found for the other seasons.