Hyphenated Analytical Techniques for Studying the Speciation and Fate of Contaminants and Nanoparticles in Waste Treatment and Bioenergy Processes

The widespread use of nanoparticles (NPs) and other potentially ecotoxic chemical compounds to enhance the quality of consumer products has raised concern about their fate in the environment. Indeed, those products have to be ultimately disposed of and along with them also NPs and contaminants could end up in landfills or in facilities where waste and nano-waste, as well as biomass products, are stored and/or treated. Among the possible pathways involving their release in the environment, this thesis' focus is in particular on gaseous emissions during two main applications, namely waste treatment and bioenergy generation. In this frame, the effect of contaminants is considered not only in terms of their toxicity but also in terms of their effect on energy efficiency or potential damages caused to the facilities along the process chain. For this purpose, new online and offline methods were developed by using hyphenated analytical techniques to achieve complementary and superior power of investigation. Firstly, the speciation of siloxane compounds were studied during bio-methane production from manure and agricultural waste. The samples were collected using a liquid quench (LQ) sampling system that concentrates condensable and non-condensable compounds in a liquid solvent in continuous contact with the gas probed, for an improved time resolution. The offline investigation required a complete method development for the combination of a separation technique, such as gas chromatography (GC), and detectors able to provide chemical information. The novelty was represented by the simultaneous use of GC with a flame ionization detector (FID) and inductively coupled plasma mass spectrometry (ICP-MS), which could fulfill the requirements of recent regulations for the specific application, with lower detection limits compared to existing methods. Secondly, the fate of zinc oxide (ZnO) NPs were investigated during the combustion of impregnated wood, as a model of nano-waste. ZnO was specifically considered because of its use in paints and waterproofing agents. The potential release of NPs during nano-waste treatment was investigated with an online method that combines an RDD (rotating disk diluter) used as conditioning and dilution unit, an SMPS (scanning mobility particle sizer) providing the particle size distribution and ICP-MS used as a multi-elemental analytical technique. An initial assessment of the performances of the RDD-SMPS-ICP-MS was required, to correct some major assumptions used in the SMPS data treatment. The technique was successfully applied even to heterogeneous matrices. The particular capability of performing online sampling and simultaneous size-resolved and elemental analysis on the off-gases produced during wood combustion was providing the needed insights to verify the predicted mechanism of reduction and further re-oxidation of ZnO nano-objects. Thanks to the calibration strategy coupling a TGA (thermogravimetric analyzer) with RDD-ICP-MS, a successful determination of their concentration was also possible. In conclusion, the development of specific hyphenated techniques was proven to be crucial to improve the capabilities of the already existent state-of-the-art methods and to develop new ones that could give more insight on the two main scientific questions that were the driving force of this thesis.

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

Prechamber autoignition in natural gas engines

Daniel Favrat, Stefan Heyne, Jan-Bernhard Vos

Unscavanged prechamber ignition has been developed at the Laboratory of Industrial Energy Systems to reduce the emissions from cogeneration spark ignition gas engines, operating with both natural gas and biogas. Demonstration has been made that a lean burn engine unit equipped with optimized prechambers allows efficient operation, while remaining below the Swiss limits [1,2]. Further development aims at using prechambers operating in autoignition mode similar to HCCI (Homogeneous charge compression ignition). The advantages are on the one hand that there is no need for maintenance and replacement of the spark plugs which usually have a limited life time while on the other hand we are expecting to benefit from the HCCI characteristics, e.g. low NOx emission levels. The prechamber configuration though should be a system easier to control than an engine operating completely in HCCI mode. The investigation of the applicability of this technique for engines used in the transport sector with rapidly changing operating conditions might be a further step in the development. In order to better understand the phenomena, simulations are done taking into account both fluid dynamics and chemical kinetics. Ignition delay measurements with mixtures of methane, ethane and propane have been conducted at the Rapid compression machine facility at the University of Lille at varying stoichiometric ratios. These measurements are used as a basis to choose an appropriate chemical mechanism for combustion simulation. The kinetic solver CHEMKIN has been used for zero-dimensional simulations at TDC conditions of the rapid compression machine to reproduce the ignition delays. Several detailed combustion mechanisms have been applied for these simulations, e.g. GRI 3.0 + RAMEC, n-Heptane and PRF mechanisms (LLNL) and Konnov’s mechanism. The aim is to obtain a reduced mechanism that will be used in combination with computational fluid dynamics. In order to do this, sensitivity and reaction pathway analysis is performed, as well as multi- objective optimization of the kinetic parameters. In cooperation with CFS engineering a coupling between the CFD code NSMB (Navier Stokes Multi Block) and the chemical solver CHEMKIN has been established enabling a simulation of the experiments conducted with the rapid compression machine. Further steps will be the design of a prechamber to be used with an experimental mono-cylinder engine and the simulation of the in-cylinder flow with prechamber to determine the influencing factors for controlling the autoignition event. Behaviour at part load as well as in transient conditions will also be investigated.

2005

Evaluation of the State-of-the-art of Biomass gasification for heat and electricity production

In the order to produce energy for the large amount of people still currently out of the national girds, different possibilities exist. For practical and economic reasons, the most popular one is the use of Diesel engines coupled with generator sets. Petrol reserves being not infinite, renewable solutions have to be found to insure a sustainable development of the poorest areas in the world. One of those could be the gasification of biomass. The latter has two advantages: Biomass is a renewable energy source and is present almost everywhere in the world: the gas produced can have various applications among them fuel for unmodified Diesel engines. Unfortunately, things are not so simple: the gas produced has a low heating value, its use in an internal combustion engine requires cleaning, biomass is not uniform through the world and technology has to be adapted for each properties, biomass supplying can product to environmental hazards if it is not strictly controlled, etc. Moreover, no standardization exists currently for the development of the technology. However, positive results have been obtained and it seems that interesting opportunities exist for the future. It requires further investments and global communication between the protagonists. The present study tries to give a complete overview of the current biomass gasification field. Some important results obtained on existing gasification plants, as well as problems encountered on technical, social, environmental and economic point of view, are also presented. Finally, some promising alternatives are proposed, as well as the main required research.