Assainissement de la décharge de Colliare à Penthaz – Etude de variantes

The landfill of Colliare is situated on the left bank of the river « la Venoge », at the place of a former gravel pit in the municipality of Penthaz. It was exploited until 1995 and many different wastes were deposited in it, such as incineration slag of household waste, grinding of cars, residues of biostabilizer, waste of construction site and materials of excavation. A water pollution due to the presence of this landfill was noticed at the beginning of the nineties, mainly by ammonium and nitrite. In one measure chromium was also found in rather important concentration. The presence of these compounds in water reflects the existence of biodegradation of the organic matter present in the mass of waste. The concentration of ammonium being higher than the limit imposed by Swiss law, a remediation is necessary. Various projects of remediation were made during the last twenty years, the main being to clean up this former landfill in order to have the possibility of creating a new one for bioactive wastes. This project was rejected by the « Grand Conseil » and the remediation of the landfill was set aside during several years. Today, the question is to study various variants of remediation to define which one would be the best for Colliare. The choice of the variants was limited either to a containment of the landfill’s surface or to bioventing. This work studies the possible implantation of these two variants, by analysing their advantages and disadvantages so as to facilitate the choice of the final solution. For that purpose, laboratory analyses were made to define the list of contaminants present in the mass of waste that risk to contaminate the water near the landfill. It was demonstrated that beside the already turn out organic pollution, the landfill contains a huge quantity of PCB and PAH as well as several heavy metals such as chromium, lead or copper. Furthermore analyses to obtain information on the quantity of biodegradable organic matter were made. It was shown that organic matter constitues only a small percentage of the mass of waste. Landfill containment is not considered as a real remediation because the contaminants stay in the site. The solution is studied here because of the various types of contaminants present in the waste. Furthermore the time it takes to implement is relatively short and it is possible to put vegetation on the site just after the installation of the mineral cover. There are thus few impacts on the fauna and the flora and the contaminants are normally not a risk anymore for the water during all the life of the containment. Bioventing has as main advantage to be a real method of remediation. The problem of its implementation in the case of Colliare is the presence of PCB and PAH in the mass of waste. Indeed biodegradation would have no effect on these compounds and the risk of water contamination would not decrease thanks to bioventing. Furthermore the small percentage of organic matter does not justify the implementation of such an installation. Finally the costs of both variants were compared. Containment costs less than bioventing. Thus the cost of bioventing is too high to implement it in addition to containment except if the decrease of greenhouse gases emissions is enough important for being exchanged on the market of carbon. The solution chosen here is landfill containment, although it is not ideal for a real remediation of the site.

Recyclage des eaux usées en irrigation

Yeli Mariam Sou

The present study takes place in Ouagadougou (Burkina Faso), a typical Sub-Saharan city where water shortage and food crisis necessitate wastewater reuse in urban agriculture. Different issues linked to this practice were studied in two components separated in two experimental sites. The first part treats about agronomic and sanitary aspects and take place in the 2iE (International Institute for Water and Environmental Engineering) experimental site of Ouagadougou. The second component was emphasised on industrial effluents impacts on irrigated soil quality and takes place in Kossodo, an industrial suburb of Ouagadougou. The 2iE site is supply with treated wastewater from domestic origin. The effluent was used to realise the following objectives: (1) managed wastewater fertilizers to fit the plant needs; (2) assess different crops sanitary quality and the effectiveness of methods used for this assessment. Three treatments were tested: (i) irrigation with the treated wastewater (ii) irrigation with the treated wastewater and fertilizers management, adjusted to plant needs and (iii) conventional treatment i.e. fresh water irrigation and total doses of commercial fertilizers. Each treatment was tested on three different crops: lettuce (Lactuca sativa), carrot (Daucus carota) and eggplant (Solanum melongena). The first objective was achieved by comparing crops yields (on basis of wet and dry matter) obtained with the different treatments. The three crops, irrigated with only wastewater, led to yield reduction between the first and the second year. At the contrary, the adjusted treatment showed higher yield for lettuce, with comparable values to conventional treatment yield. However, the effects on carrot and eggplant did not demonstrate better results; indicating that further investigations must be completed for crops with longer growing periods. Most likely, the fertilizers management should better correspond to the crop period demand. The sanitary assessment (second objective) was performed by measuring the heavy metals concentration (Cd, Cu, Pb, Ni, Cr) and the faecal levels (faecal coliform, Escherichia coli and four pathogens among which Salmonella typhimirium and Vibrio cholerae). Chromocult Coliform Agar medium was used for simultaneous detection of faecal coliform and Escherichia coli whereas pathogens were analysed by Polymerase Chain Reaction (PCR). From methodological point of view, faecal coliform were not sufficiently discriminatory in the case of this study since they were naturally present in the soil as well as in the fresh water. At the contrary, Escherichia coli were better linked to wastewater contamination. However, some "false positive" results were detected meaning that each presumptive colony of Escherichia coli must be confirmed. Nevertheless, microbial quality assessment indicated no Escherichia coli on edible parts of carrot or eggplant irrigated with wastewater. Carrots were expected to have the poorest microbiological quality. Therefore carrot root bacterial quality must be further examined. Results on eggplant are not surprising as these vegetables are somewhat far from the ground and they receive significant solar radiation which acts like a disinfectant. Lettuce from wastewater treatment plots, however, exhibited presence of Escherichia coli, meaning that lettuce is likely to be contaminated by pathogens. However, no pathogens were detected neither on crops irrigated with fresh water nor on those irrigated with wastewater. Heavy metals results demonstrated that the crop's consumption did not involve higher risk for consumers when the vegetables were irrigated with domestic wastewater, in comparison with fresh water irrigation. Kossodo treatment plant receives mainly industrial wastewater, which are characterized by high levels of sodium and bicarbonates. The treated wastewater supplies a market garden in which space has been defined for the study of this second component. The main objective was to assess the impact of treated wastewater on soil quality during two years of irrigation. Early in the second year, the presence of black spots, suspected to be black alkali (dissolved organic matter), appeared at the surface of plots irrigated with treated wastewater. These indications led to put forward the hypothesis of alkalinisation/sodisation on soil receiving wastewater. The methodological approach used was based on in situ measurement of infiltration at the end of the second year of irrigation, supplemented by shrinkage curve modelling and chemical analysis. The hypothesis of an alkalinization/sodisation and dissolved organic matter (black alkali) presence in plots irrigated with treated wastewater were validated by the chemical analysis. Shrinkage curve modelling showed a reduction of the structural porosity on wastewater irrigated plots. The reduction was more marked in the subsurface horizons than in surface, which is probably caused by dispersed clay leached in depth. These structural changes were confirmed in situ by an infiltration capacity greatly reduced on plots irrigated with treated wastewater, compared to control plots (irrigated with fresh water) where the infiltration capacity is higher and comparable to that of non-irrigated soil. The study confirmed the fertilizing value of domestic wastewater while emphasizing the need to concentrate future investigations on sustainable effluent/fertilizers management. The sanitary assessment with different crops regarding their respective distances to the soil was very useful since it showed the strong interaction of soil microbial community on the crop microbial quality. It also revealed the importance to determine a faecal indicator for the crop, specifically related to wastewater contamination. Soil quality assessment reiterated the necessity to verify wastewater quality before its reuse in agriculture. In the case of this study, the sodic and alkaline properties of the industrial effluents make them definitively unfit for irrigation.

EPFL2009

Fate of volatile fluorinated compounds in the subsurface

Christian Balsiger

Since their discovery around 1930, the synthetic compounds of the class of chlorofluorocarbons (CFCs) have been produced and used worldwide at very large scale. Their physico-chemical properties (non-flammability, chemical inertia, miscibility with water and oil, compatibility with many metals and plastics, solvent capacity) have made them ideal candidates for several applications, such as refrigerant fluids, aerosol propellants, foam blowing agents, or as solvents or intermediates of chemical synthesis. In the 70', it was demonstrated that following their release in the atmosphere, they are implicated in the process leading to the commonly called stratospheric ozone hole. The governments of several industrialised country have thus signed a protocol with the objective to stop the production and use of CFCs. CFCs have been increasingly replaced by compounds with similar structure, the hydrochlorofluorocarbons (HCFCs), but whose reactivity in the lower layers of the atmosphere is quite different from that of CFCs. Due to their chemical inertia, CFCs has been used as tracers for surface and groundwater datation. During such investigations, the biodegradability of these compounds and the existence of punctual pollution sources in soil and groundwater have been evidenced. It has been demonstrated that some of these compounds can be dechlorinated under anoxic conditions producing other compounds with sometimes higher toxicity and higher water solubility, and resulting in a risk linked to the consumption of natural groundwater. The goal of this thesis was to get indications about reductive transformations of CFCs and especially HCFCs in Swiss aquifers and landfills, on the potential of different microbial communities to reductively dechlorinate certain compounds, and under which redox conditions the transformations occur in aquifer systems. Data concerning the production, use, emission, regulation, as well as the biodegradability and toxicity of these compounds are presented in chapter 1 and in the appendix. The analytical methods developed and used during this work are presented in chapter 2. Particularly, a versatile analytical system allowing the measure of trace but also higher concentrations in different media, solid or aqueous, has been set up and used during this work. CFCs and HCFCs were analyzed at 3 sites in Switzerland. Samples were collected from a natural groundwater in which a chloroethene plume had been observed, from an old landfill closed in 1980, and from a more recent bioactive landfill constructed in horizontal layers. In addition, the behaviour of different CFCs and HCFCs was studied in microcosms inoculated with sludge originating from several sewage treatment plants in the canton of Vaud, and with a sediment originating from a contaminated aquifer in Holland. The studied CFCs and HCFCs were furthermore injected at the inlet of a 1.2 m height column filled with the aquifer sediment from Holland. In this quasi natural aquifer, the oxido-reductive conditions were modified during the experiment in order to investigate the conditions at which the biodegradation occurred. The field studies showed that CFCs and HCFCs are present in aquifers and landfills, and there were indications that their transformation also occurs there. Estimations of half-life times indicated that the reductive dechlorination occurred at slow rates. This could be due to the low temperatures of natural groundwater systems and other factors linked to the hydro-geological properties of the natural environment such as dispersion, sorption or partitionning. In the microcosms inoculated with sludge, CFC-11 was transformed to HCFC-21, the latter being further dechlorinated to HCFC-31. HCFC-123a and chlorotrifluoroethene (CTFE) were produced simultaneously from CFC-113. Inhibition of methanogesis with 2 bromoethane sulfonate decreased significantly the degradation rate of CFC-11, emphasizing the importance of the role of methanogens in the degradation process. In the microcosms inoculated with the contaminated sediment, the transformation of CFC-11 also occurred, but was not accompanied with methane production, as it was the case in the suldge microcosms. Moreover, the presence of acetate, lactate and butyrate in the microcosms containing CFC-11 suggested that methanogens were inhibited in the presence of CFC-11. CFC-113 was transformed in the same way as in the microcosms inoculated with the sludge; however, the produced CTFE was further transformed to trifluoroethene (TFE). Production of HCFC-151b from HCFC-141b was also observed. In the column filled with aquifer material, only the transformations of CFC-11 and CFC-113 were observed, which is probably due to the short residence time in the column (~10 days), during which the transformation of the other compounds was not sufficiently pronounced. The increasingly reducing conditions in the column were accompanied with an increase of the degradation rates of CFC-11 and CFC-113, with a maximum reached in presence of methanogenesis. The addition of sulfate in the artificial groundwater decreased the biodegradation rates of the two compounds, and the concentration of their transformation products was simultaneously increased. This suggests that these products become more persistent under sulfate-reducing conditions. Natural attenuation designates all the processes leading to the decrease of the concentration of organic compounds migrating from a pollution source throughout a natural environment. Whereas natural attenuation or enhanced natural attenuation seem adequate for several classes of compounds, the absence of defluorination reaction of CFCs and HCFCs reported in this work suggests the use of other remediation techniques for the decontamination of sites polluted with these compounds. Indeed, the transformation products of CFCs and HCFCs still contain a fluorine atom and are not less harmfull to the environment than the parent compounds. In addition, the use of CFCs as age-dating tracers in groundwater is not recommended under anoxic conditions, as it was demonstrated here that they are not stable in such environments. The HCFCs on the other hand seem to be more persistent, and it is primordial to decrease rapidly their production and release in the environment.

EPFL2004

Advancements in heavy metals removal from effluents employing nano-adsorbents: Way towards cleaner production

Edgard Gnansounou, Baskar Gurunathan

Due to the development in science field which gives not only benefit but also introducesundesirable pollution to the environment. This pollution is due to poor discharge activities of industrial effluents into the soil and water bodies, surface run off from fields of agricultural lands, dumping of untreated wastes by municipalities, and mining activites, which deteriorates the cardinal virtue of our environment and causes menace to human health and life. Heavy metal(s), a natural constituent on earth's crust and economic important mineral, due to its recalcitrant effects creates heavy metal pollution which affects food chain and also reduces the quality of water. For this, many researchers have performed studies to find efficient methods for wastewater remediation. One of the most promising methods from economic point of view is adsorption, which is simple in design, but leads to use of a wide range of adsorbents and ease of operations. Due to advances in nanotechnology, many nanomaterials were used as adsorbents for wastewater remediation, because of their efficiency. Many researchers have reported that nanoadsorbents are unmitigatedly a fruitful solution to address this world's problem. This review presents a potent view on various classes of nanoadsorbents and their application to wastewater treatment. It provides a bird's eye view of the suitability of different types of nanomaterials for remediation of wastewater and Backspace gives up-to-date information about polymer based and silica-based nanoadsorbents.