Pollutant | EPFL Graph Search

A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oil) or anthropogenic in origin (i.e. manufactured materials or byproducts). Pollutants result in environmental pollution or become public health concerns when they reach a concentration high enough to have significant negative impacts. A pollutant may cause long- or short-term damage by changing the growth rate of plant or animal species, or by interfering with resources used by humans, human health or wellbeing, or property values. Some pollutants are biodegradable and therefore will not persist in the environment in the long term. However, the degradation products of some pollutants are themselves polluting such as the products DDE and DDD produced from the degradation of DDT. Pollution has widespread negative impacts on the environment.

Assessment of microbial community changes and limiting factors during bioremediation of hydrocarbon-polluted soil with new miniaturized physiological methods

Karin Kaufmann

Due to human activities, organic pollutants are spilled to the environment where they threaten public health, often as contaminants of soil or groundwater. Living organisms are able to transform or mineralize many organic pollutants, and bioremediation techniques have been developed to remove pollutants from a contaminated site. However, fast and easy methods to document both the efficacy of bioremediation and the changes in soil microbial communities during bioremediation are not well developed. The major aim of this thesis was to develop miniaturized methods targeting the physiology of microbial communities during pollutant degradation in soil and to assess pollution-induced community changes. Furthermore, the methods should identify factors limiting efficient pollutant biodegradation. Petroleum hydrocarbons have been chosen as pollutants because these compounds are frequently spilled, readily water-soluble, partly toxic and carcinogenic, and therefore undesirable in soils and drinking water supplies. The influence of petroleum hydrocarbons on a microbial community in the vadose zone was assessed under field conditions. An artificial hydrocarbon mixture consisting of volatile and semi-volatile compounds similar to jet-fuel was emplaced in a previously uncontaminated vadose zone in nutrient-poor glacial melt water sand. The experiment included monitoring of microbial parameters and CO2 concentrations in soil gas over 3 months, in- and outside the hydrocarbon vapor plume that formed around the buried petroleum. Microbial and chemical analyses of vadose zone samples were performed on material from 9 cores drilled on 3 days at 3 distances from the buried petroleum mass to 3.3 m depth. Significantly elevated CO2 concentrations were observed after contamination. Total cell numbers as determined by fluorescence microscopy were strongly correlated with soil organic carbon and nitrogen content but varied little with contamination. Redundancy analysis (RDA) allowed direct analysis of effects of selected environmental variables or the artificial contamination on microbiological parameters. Variation in biomass and CO2 production was to 46 % explained by soil parameters and to 39.8 % by the duration of contamination. The microbial community structure was assessed by community-level physiological profile analysis using BiologTM EcoPlates. Only 35.9 % of variation in BiologTM data could be attributed to soil parameters and contamination, however, the samples with greatest exposure to hydrocarbons grouped together on RDA plots. It is concluded that at this nutrient-poor site, the microbial community was dominated by the natural heterogeneity and that the influence of petroleum hydrocarbon vapor was weak. BiologTM Eco-Plates combined with RDA were able to distinguish between samples with high and low hydrocarbon exposure. However, the method was not sensitive enough to produce consistent patterns in three replicates when extracts from subsurface soils with low cell numbers were inoculated. A more sensitive, MPN-based system was therefore developed and its ability to provide information about specific pollutant degraders was tested in alluvial sand. Eight dilutions of sand extracts were inoculated on medium- and substrate-containing polypropylene deep-well plates. To keep the concentrations of the volatile substrates constant over several days of incubation without intoxicating the soil community, a substrate-containing organic carrier phase was applied to each vial. The biochemically inert 2,2,4,4,6,8,8-heptamethylnonane (HMN) was appropriate for this purpose. Thus, the volatile substrates partition from HMN into the microorganism-containing soil water where they achieve relatively low concentrations. The sensitive watersoluble tetrazolium dye (WST-1) was added to each well after 7 days incubation to detect dehydrogenase activity. A dark yellow signal was developed for the substrates toluene, n-octane, n-dodecane, 1,2,4-trimethylbenzene and methylcyclohexane but not for isooctane, being strongest in n-alkane amended wells. With this method, more hydrocarbon degrading bacteria were detected in an alluvial sand exposed to kerosene for 72 hours compared to the community in the pristine sand. Both communities were mainly composed of n-alkane degraders. Although encouraging results were achieved, we noticed that the tetrazolium reduction was inhibited in some cases. Wells with high cell numbers, in which obvious growth occurred, did not produce a signal. In a next step, the two-liquid phase system with HMN was applied to modify a miniaturized respiration detection system using whole soil samples instead of soil extracts (Campbell et al., AEM 69, p. 3593). Soil was incubated in deep-well plates in presence of single volatile organic hydrocarbons. The carrier phase was added to the interstitial space in a bead layer on the bottom of the well (below the soil sample), and the hydrocarbons diffused into the soil-water. The soil activity was determined by means of an agar plate containing a pH indicator, which changes color as a function of the produced CO2. Physiological profiles specific to petroleum hydrocarbons in pristine and contaminated soils were assessed. The substrate concentrations, which induced highest microbial activity, as well as concentrations causing inhibition, were determined with effect-concentration curves. Community-level physiological profiles based on hydrocarbon degradation were obtained by applying multivariate analysis on the CO2 yields. The first measurement period of 0-6 hours after addition of relatively high hydrocarbon concentrations to the system yields values, which best separated soil types as well as pristine and contaminated soils. If low concentrations were applied, we obtained only significant separations after 24 hours incubation, probably after a growth step. The same micro-respiration system equipped with a 14CO2 detection plate was applied to study N and P limitation of aerobic mineralization of 14C-toluene in a soil previously exposed to petroleum. Significant nutrient limitation during short-term tests (24-48 hours) was identified and the optimized combination of nutrient addition was determined. Conclusively, miniaturized physiological methods have been proven to detect soil microbial community changes in petroleum hydrocarbon-contaminated soils. Adding an organic carrier phase to the miniaturized systems allowed assuring a volatile organic hydrocarbon supply in non-toxic concentrations in the soil water or the medium for several days. Thus simple, cost-effective systems to investigate the soil community during bioremediation and to address questions of nutrient shortage in soils have been provided with this thesis.

EPFL2004

Mécanismes d'action du TiO2 illuminé sur Escherichia Coli

Gaëtan Gogniat

The increase of bacterial resistance against various disinfection processes is a worrying phenomenon. As a consequence, the search for alternative techniques for fighting micro-organisms has become one of the major issues of these last few years. In this domain, water treatment is an important preoccupation for many states, either to guarantee the quality of drinking water supply or to detoxify industrial effluents, charged with chemically or biologically pollutants. The financing of this thesis project was provided by the European project AQUACAT. This project aims at evaluating an emerging technology, the titanium dioxide (TiO2) photocatalysis, as an alternative to the traditional water treatments. This technique is based on the illumination of the catalyst, which thus generates reactive oxygen species (ROS), particularly hydroxyls radicals. TiO2 photocatalysis can be used as a water treatment by detoxifying organic compounds and inactivate micro-organisms. Moreover, its bactericidal activity have a promising biomedical future, by killing cancerous cells for example. Although the bactericidal action of the TiO2 photocatalysis is well documented, its mode of action on bacteria was not yet well defined. The objective of this thesis is to contribute to a better comprehension of the mode of action of the TiO2 photocatalysis on the bacterium Escherichia coli. Few microbiologists ever worked on this subject. A review of published articles on the mode of action of TiO2 photocatalysis showed some experimental failures. Moreover, dogmas related to TiO2 photocatalysis showed contradictions, which will be discussed in this thesis. This thesis is divided in four chapters, including two major sections: i) interaction between TiO2 particles, bacteria, biomolecules and salts and ii) the defence mechanisms of the bacterial cells against TiO2 photocatalysis. The first chapter shows that bacterial cells are adsorbed onto TiO2 particles. So as to demonstrate this feature, bacterial cells and TiO2 particles were mix in the presence of two salts affecting at different degrees the effectiveness of TiO2 photocatalysis rate. In the presence of NaCl-KCl, photocatalysis was very effective and the cultivability of the cells decreased at the beginning of the illumination phase. On the contrary, in a phosphate solution, a latency phase of 20 minutes was observed. Using flow cytometry and microscopic observations, we observed very distinctly that the bactericidal effect begun when the cells started to be adsorbed on TiO2 particles. Bacterial adsorption on TiO2 particles could be correlated to the loss of cell cultivability and also to the loss of membrane integrity, measured by flow cytometry. We then studied the interaction between biomolecules (proteins and DNA), bacterial cells and TiO2 particles. Biomolecules strongly adsorbed onto TiO2 particles in a NaCl-KCl solution (up to 60 µg protein per ml of catalyst). A desorption buffer composed of phosphate (50mM, pH 7.0) and SDS (0.1%) is able to desorb 12% only of the proteins. When bacterial cells were in presence of a cell crude extract corresponding to the quantity of proteins belonging to their population (equal to 12µg protein/ml for 2×107 bacteria /ml), it was observed that the effectiveness of the treatment was decreased, suggesting that cell crude extract protected bacterial cells from the photocatalytical treatment. So as to improve our understanding of the mode of action of the TiO2 on the bacterial cells, we compared the survival of E. coli mutants with the wild type one. Knowing that TiO2 generated ROS, we assayed mutant affected in their defence mechanisms against these molecules. Thus, the sensitivity of mutants defected in the induction of DNA repair and of DNA protection systems suggested the induction of cytoplasmic damage by the photocatalytical process. We could also highlight the importance of the Fenton reaction and the formation of hydroxyls radicals in this inactivation process. The hypothesis is that these hydroxyl radicals were also produced in the cells, following an increase in reactive iron and hydrogen peroxide. Interestingly, the loss of E. coli cultivability after TiO2 illumination appeared not only during the illumination, but also when cells were incubate on Petri plates, whereas TiO2 was not illuminated. Thus bacteria underwent a secondary stress, leading also to their loss of cultivability. Finally, we identified genes expressed in the response to the treatment (primary stress) and after a short incubation in a rich culture medium to 37 °C (secondary stress). Thus after an illumination time (100% of bacteria were cultivable) and an other one which show first signs of letality (80% of the cultivable bacteria), no difference in expression of the mRNA could be observed with the transcriptome analysis (DNA chips) of the E. coli genome. On the other hand, as soon as the cell were resuspended in a rich medium after the treatment during only 5 minutes, we could observe differences, by a factor higher than two, in the induction of certain genes. The totality of genes induced during the TiO2 photocatalysis were repressed by Fur and were implied in the iron transport.

EPFL2006

Helio-photocatalytic enhancement of the biodegradation of biorecalcitrant pollutants in water

Simeon Kenfack

The importance of the photocatalytic treatment of water is continuously growing since the 80s. In spite of the well management of the existing biological water treatment plants and the constant reinforcement of the wastewater discharge standards, the development of new water depolluting processes among which the photocatalysis is still relevant. It is recognized that certain chemicals mostly from the synthetic chemistry are not or could only be biodegradable under very critical conditions. When these "biorecalcitrant" pollutants are rejected in a biological wastewater treatment plant, they very often cross it without being degraded and thus, they accumulate in the environment and/or in the living beings. Some of them like the phthalates and the pesticides are known for their carcinogenic and mutagen effects or, they induce hormonal disruptions in the animals, including humans. In general, all the Advanced Oxidation Processes (AOP) whose characteristic is to generate hydroxyls radicals (OH) are able to degrade most of the organic molecules including the biorecalcitrant chemicals. As a technology using the photons emitted by a light source to excite a catalyst and facilitate the generation of the 'OH radicals, the photocatalysis would be a more environmental compatible and less expensive process for depolluting such chemicals, if the light source is natural: the sun. For the first time, a study of potential application in the field of helio- photocatalysis was explored in a sub-Saharan Africa country (Burkina Faso), making profitable the significant solar radiation present in that country, to validate certain results obtained using appropriated experimental and analytical methods at the Laboratory for Environmental Biotechnology (LBE) at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. The main objective of this thesis was to contribute to evaluate some physicochemical and technical rules which guide the scaling up processing of the helio-photo-Fenton process. To achieve this, the work was organized in several phases of laboratory work at the EPFL and field apply work at the Ecole Inter-Etats d'Ingénieurs de l'Equipement Rural (EIER) of Ouagadougou in Burkina Faso. To mitigate the deficit of sophisticated analytical material during the field work's periods, a simple analytical method requiring relatively modest equipment was developed and validated in the laboratory and on the field. This thesis is organized in 5 chapters of which the first focuses on the problems of this research and presents the fundamental principles of the photocatalytic processes. Chapter 2 presents the systematic development of a low cost analytical method built up and validated in the laboratory for field's applied studies on three phthalates: the dimethyl phthalate (DMP), the diethyl phthalate (DEP) and the Diallyl phthalate (DAP). The chapter 3 focuses on the study of the optimal parameters influencing the helio-photodegradation of the DEP. In the chapter 4, two case studies on the enhancement of the biodegradability of some biorecalcitrants wastewaters of which, the first evaluates the possibility of integrating the photocatalysis into a global strategy of managing the effluents of a chemical industry and the other treat problem of the depollution of the water polluted by a pesticide are presented. The last chapter presents some modelling approaches allowing to evaluate the solar UVA energy (needed for the helio-photocatalysis) basing on the equation of the solar UVA irradiation which was proposed and tested with the one year solar data of Ouagadougou.

EPFL2006

Assessment of microbial community changes and limiting factors during bioremediation of hydrocarbon-polluted soil with new miniaturized physiological methods

Karin Kaufmann

EPFL2004

Mécanismes d'action du TiO2 illuminé sur Escherichia Coli

Gaëtan Gogniat

EPFL2006

Helio-photocatalytic enhancement of the biodegradation of biorecalcitrant pollutants in water

Simeon Kenfack

EPFL2006