Estágio realizado na technische Universiteit Eindhoven e orientado pelo Prof. A. B. de Haan e Eng.º B. Burghoff / Tese de mestrado integrado. Engenharia Química. Faculdade de Engenharia. Universidade do Porto. 2008

ABSTRACT This study focuses on the dissolution and near-source attenuation of oxygenated gasoline hydrocarbons in groundwater from two gasoline residual sources: one containing gasoline with 9.8% methyl tert butyl alcohol (MTBE) and 0.2% tert-butyl alcohol (TBA) (GMT source) and the other containing gasoline with 10% ethanol (E10 source). The sources were injected into a shallow sand aquifer, leaving a residual plume to dissolve under natural gradient conditions. The MTBE plume (from the GMT source) and the ethanol plume (from the E10 source) were compared with predictions by the BIONAPL numerical model assuming ideal source dissolution and no biodegradation of the oxygenates or aromatic hydrocarbons. While the complete mass of injected MTBE appeared to pass row 2, little MTBE was found further downgradient. This mass loss was considered to be an artifact of the monitoring system and of possible biodegradation. The ethanol mass flux was better captured in the E10 gate. Essentially all the ethanol from the E10 source also passed row 2, but, the ethanol mass flux decreased somewhat from row 2 to row 4. The better mass recovery may reflect that the ethanol plume remained more in the center of the monitoring network as compared to the MTBE plume some of which may have bypassed the monitoring fence. MTBE, TBA, and ethanol in the model were assumed to dissolve at equilibrium. The MTBE and TBA concentration breakthrough curves are generally consistent with equilibrium dissolution. However, the mass flux values suggest non ideal dissolution. The ethanol concentration breakthrough curves and mass flux are consistent with equilibrium dissolution. Also, the observed concentrations were often higher than predicted at later times. These features could be due to non-equilibrium (kinetically-limited) dissolution However, non-ideal source conditions may have arisen due to most of the oxygenates being dissolved into the water injected along with the gasolines thus distributing the residual gasoline in a non-uniform manner. The concentrations of aromatics are higher than expected from the BIONAPL model and are consistent with tailing expected with non-equilibrium dissolution. However, the probable complexity of the source concentration distribution likely account for much of the concentrations variability. There were insufficient electron acceptors to support complete mineralization of either the oxygenates or the BTX-TMB compounds. Although, evidence of weak MTBE biodegradation was found, the major mass loss seemed to be related to the uncertainties in the monitoring network. Some ethanol mass loss could be attributed to fermentation to organic acids (which were not sought in the field experiment). The persistence of BTX-TMB through the gates seemed to be slightly greater in the presence of ethanol. The field study was also used to test the Ratio Mass Estimation (RME) method of estimating the initial NAPL mass in the source from downgradient contaminant concentrations. The method was found reasonably reliable if the downgradient concentrations were collected close to the source where biodegradation was minor.

ABSTRACT This study focuses on the dissolution and near-source attenuation of oxygenated gasoline hydrocarbons in groundwater from two gasoline residual sources: one containing gasoline with 9.8% methyl tert butyl alcohol (MTBE) and 0.2% tert-butyl alcohol (TBA) (GMT source) and the other containing gasoline with 10% ethanol (E10 source). The sources were injected into a shallow sand aquifer, leaving a residual plume to dissolve under natural gradient conditions. The MTBE plume (from the GMT source) and the ethanol plume (from the E10 source) were compared with predictions by the BIONAPL numerical model assuming ideal source dissolution and no biodegradation of the oxygenates or aromatic hydrocarbons. While the complete mass of injected MTBE appeared to pass row 2, little MTBE was found further downgradient. This mass loss was considered to be an artifact of the monitoring system and of possible biodegradation. The ethanol mass flux was better captured in the E10 gate. Essentially all the ethanol from the E10 source also passed row 2, but, the ethanol mass flux decreased somewhat from row 2 to row 4. The better mass recovery may reflect that the ethanol plume remained more in the center of the monitoring network as compared to the MTBE plume some of which may have bypassed the monitoring fence. MTBE, TBA, and ethanol in the model were assumed to dissolve at equilibrium. The MTBE and TBA concentration breakthrough curves are generally consistent with equilibrium dissolution. However, the mass flux values suggest non ideal dissolution. The ethanol concentration breakthrough curves and mass flux are consistent with equilibrium dissolution. Also, the observed concentrations were often higher than predicted at later times. These features could be due to non-equilibrium (kinetically-limited) dissolution However, non-ideal source conditions may have arisen due to most of the oxygenates being dissolved into the water injected along with the gasolines thus distributing the residual gasoline in a non-uniform manner. The concentrations of aromatics are higher than expected from the BIONAPL model and are consistent with tailing expected with non-equilibrium dissolution. However, the probable complexity of the source concentration distribution likely account for much of the concentrations variability. There were insufficient electron acceptors to support complete mineralization of either the oxygenates or the BTX-TMB compounds. Although, evidence of weak MTBE biodegradation was found, the major mass loss seemed to be related to the uncertainties in the monitoring network. Some ethanol mass loss could be attributed to fermentation to organic acids (which were not sought in the field experiment). The persistence of BTX-TMB through the gates seemed to be slightly greater in the presence of ethanol. The field study was also used to test the Ratio Mass Estimation (RME) method of estimating the initial NAPL mass in the source from downgradient contaminant concentrations. The method was found reasonably reliable if the downgradient concentrations were collected close to the source where biodegradation was minor.

Many parts of the world are facing water crises due to the lack of clean drinking water. Growing industrialization in many areas and extensive use of chemicals for various concerns has increased the burden of deleterious contaminants in drinking water especially in developing countries. It is reported that nearly half of the population in developing countries suffers from health problems associated with lack of potable drinking water as well as the presence of microbiologically contaminated water [1] . Synthetic and natural organic contaminants are considered among the most undesirable contaminants found in water. Various treatment processes are applied for the removal of organic contaminants from water including reverse osmosis membranes, ion exchange, oxidation, nanofiltration, and adsorption. The adsorption process is a widely-used technology for the removal of organic compounds from water. In this work, the adsorption of chloroform and methyl tertiary butyl ether (MTBE) onto granular zeolites was investigated. Zeolites were specifically chosen because they have shown higher efficiency in removing certain organics from water than granular activated carbon (GAC). Batch adsorption experiments to evaluate the effectiveness of several granular zeolites for the removal of MTBE and chloroform from water were conducted and the results compared with GAC performance. Results of these batch equilibrium experiments showed that ZSM-5 was the granular zeolite adsorbent with the greatest removal capacity for MTBE and chloroform from water, and outperformed GAC. Fixed-bed adsorption experiments with MTBE and chloroform were performed using granular ZSM-5. Breakthrough curves obtained from these column experiments were used to understand and predict the dynamic behavior of fixed bed adsorbers with granular ZSM-5. The ii film pore and surface diffusion model (FPSDM) was fit to the breakthrough curve data obtained from the fixed bed adsorption experiments. The FPSDM model takes into account the effects of axial dispersion, film diffusion, and intraparticle diffusion mechanisms during fixed bed adsorption. Generally, good agreement was obtained between the FPSDM simulated results and experimental breakthrough profiles. This study demonstrated that film diffusion is the primary controlling mass transfer mechanism and therefore must be accurately determined for good breakthrough predictions.

Methyl Tertiary-Butyl Ether (MTBE) contamination of groundwater and surface waters has become a relevant environmental and public safety concern in recent years. This anthropogenic compound is now persistent at low concentrations in several valuable ground and surface water locations within the United States due largely to the widespread production of MTBE for use as a fuel oxygenate in conjunction with negligent underground storage practices during the 1980's and 1990's. Though there are several treatment strategies for the remediation of MTBE spill sites, the most efficient strategy may be adsorption of MTBE by a packed column of silicalite-1 adsorbent. Effective adaption of this technology requires cheap production of silicalite-1 sorbent packing particles on the order of 3 millimeters diameter. This work entails the development of a new synthesis process which results in sufficient in-situ crystallization of silicalite-1 aggregates within a 3 millimeter spherical amorphous silica gel source. The crystal aggregates sizes can be tuned from 5 to 70 µm, depending on synthesis parameters, and the finished silicalite-1 aggregate particle takes the shape of the amorphous gel source. These aggregate particles, when containing a small amorphous core, should be suitable for packed adsorption column applications. Multiple hydrothermal synthesis experiments were performed by batch methods featuring silica gel spheres as the sole silica source for the batch. Zeolite nucleation and crystal growth were demonstrated throughout the amorphous bead. Synthesis parameters were optimized both for short synthesis times, optimal mechanical properties, and cost effectiveness. The influence of product crystal size on particle hardness was also investigated. The packing production process is sufficiently ready for supporting pilot scale adsorption studies.

Aqua, a commercial product manufactured by BiOWiSH® Technologies, was utilized in this research to study its effectiveness to biodegrade methyl tert-butyl ether (MTBE) and tert-butyl alcohol (TBA). Microcosms containing varying concentrations of MTBE and TBA as well as a growth media and mineral salt solution were examined. Analytical instrumentation used in this study included the use of a gas chromatograph-mass spectrometer (GC/MS) to determine concentrations of MTBE and TBA and a spectrophotometer to extrapolate approximate active biomass concentrations in each experiment. Four different environmental conditions were tested for both MTBE and TBA. The environmental conditions tested for each contaminant included: biodegradation under aerobic conditions, biodegradation under anaerobic conditions, biodegradation under denitrifying conditions, and biodegradation under aerobic conditions with glucose present. This study concluded that there is potential for degradation of MTBE and TBA using Aqua under the conditions tested. Maximum MTBE biodegradation was observed under aerobic conditions which yielded a first order rate constant of 0.019/hour and a 99.8 percent decrease in MTBE over 14 days. Maximum TBA biodegradation was observed under aerobic conditions with glucose present which yielded a first rate order constant of 0.009/hour and a 95.03 percent decrease in TBA concentrations over 14 days. It is presumed that under both conditions a monooxygenase enzymatic reaction involving Cytochrome P-450 aids in breaking down both MTBE and TBA. However, the results presented are indicative of biodegradation under lab conditions with little to no interference. Further research is needed to determine the effectiveness of Aqua utilizing groundwater or soil samples from MTBE or TBA contaminated sites in order to truly analyze Aqua’s potential to be used as a bioaugmentation product in real world applications.

<p>The most widely used gasoline additive methyl tert-butyl ether (MTBE) has been questioned recently, since frequent detection of this compound in groundwater indicates that it could be a risk to our environment. Consequently, legislative efforts have been made by some local governments to phase out the use of MTBE. Among a number of alternative substitutes, ethyl tert-butyl (ETBE) seems to be the more promised one due to its lower water solubility, suggesting that it could pose less impact to our water supply. However, a thorough understanding of its environmental fate is needed before ETBE is widely accepted as a more environmentally friendly gasoline additive. As a part of this effort, the degradation of MTBE and ETBE as well as their effects on the fate of aromatic gasoline components, i.e. BTEX (benzene, toluene, ethyl-benzene and xylenes) were studied on two soils contaminated with MTBE-blended or ETBE-blended gasoline. During a period of 5 months, the general aerobic degradation of the gasoline and its different additives were monitored by gas chromatography – thermal conductivity detection (GC-TCD) and concentration changes of MTBE and ETBE were monitored with the help of gas chromatography - mass spectrometry (GC-MS). The results of this study showed that the degradation of MTBE, ETBE and BTEX occurred in all the systems, nevertheless MTBE and ETBE degraded far more slowly in contrast with the degradation of BTEX, indicating that MTBE and ETBE are more persistent. When the degradation of MTBE and ETBE were compared, ETBE decreased a little faster than MTBE, implying that ETBE advantages slightly in degradation over MTBE. Concerning the effects of MTBE and ETBE on the fate of BTEX, the results showed that MTBE might enhance whereas ETBE might inhibit the degradation of BTEX though at a lower level. In addition, less degradation of MTBE and ETBE was observed in organic-rich soil in all the cases, probably because that there are more other substrates available for the microorganisms in organic-rich soil.</p>

The most widely used gasoline additive methyl tert-butyl ether (MTBE) has been questioned recently, since frequent detection of this compound in groundwater indicates that it could be a risk to our environment. Consequently, legislative efforts have been made by some local governments to phase out the use of MTBE. Among a number of alternative substitutes, ethyl tert-butyl (ETBE) seems to be the more promised one due to its lower water solubility, suggesting that it could pose less impact to our water supply. However, a thorough understanding of its environmental fate is needed before ETBE is widely accepted as a more environmentally friendly gasoline additive. As a part of this effort, the degradation of MTBE and ETBE as well as their effects on the fate of aromatic gasoline components, i.e. BTEX (benzene, toluene, ethyl-benzene and xylenes) were studied on two soils contaminated with MTBE-blended or ETBE-blended gasoline. During a period of 5 months, the general aerobic degradation of the gasoline and its different additives were monitored by gas chromatography – thermal conductivity detection (GC-TCD) and concentration changes of MTBE and ETBE were monitored with the help of gas chromatography - mass spectrometry (GC-MS). The results of this study showed that the degradation of MTBE, ETBE and BTEX occurred in all the systems, nevertheless MTBE and ETBE degraded far more slowly in contrast with the degradation of BTEX, indicating that MTBE and ETBE are more persistent. When the degradation of MTBE and ETBE were compared, ETBE decreased a little faster than MTBE, implying that ETBE advantages slightly in degradation over MTBE. Concerning the effects of MTBE and ETBE on the fate of BTEX, the results showed that MTBE might enhance whereas ETBE might inhibit the degradation of BTEX though at a lower level. In addition, less degradation of MTBE and ETBE was observed in organic-rich soil in all the cases, probably because that there are more other substrates available for the microorganisms in organic-rich soil.

In the last years, due to an increasing concern about the possible harmful effects of the gas emissions of the continuous gasoline use, their compositions have changed considerably. The lead additives ban and the aromatic compounds content limitation has caused the worldwide expansion of the use of fuel oxygenates. These compounds are mainly molecules with an atom of oxygen inside its structure. Usually they are ethers or alcohols. The most used worldwide is methyl tert-butyl ether (MTBE) followed by ethyl tert-butyl ether (ETBE). These compounds because of their physical and chemical properties have become persistent and recalcitrant pollutants in the groundwaters of the entire world.Due to the problem generate by the contamination of water resources is important to go deeper in the knowledge of the behaviour of fuel oxygenates in the environment in order to obtain tools that let us model and study their environmental dispersion and remediation. This doctoral thesis offers an important thermodynamical study of these compounds and analyzes different remediation techniques.The work is structured in four chapter well differentiated. The first one consists of an introduction to the problem, the current situation of thermodynamical information and the existent techniques for the water treatment.The second chapter is focused on obtaining and improving the thermodynamical information. It is studied how temperature affect to the interactions of fuel oxygenates with different gasoline compounds such us BTEX (benzene, toluene, ethylbenzene and xylenes), alcans or degradation products like tert-butyl alcohol. In this chapter is included new thermodynamical information in terms of physical properties (density and speed of sound), vapor-liquid equilibria and liquid-liquid equilibria (as water solubility). As a result have been characterized 25 binary systems and their pure compounds in terms of physical property, 3 vapor liquid equilibria and finally the study of water solubility of the ethers most used in gasoline blending as temperature function.The third chapter is focused from a technological point of view. Here it is studied thermodynamically, different conventional remediation techniques fort he MTBE and ETBE like the adsorption onto activated carbon and batch air stripping. It is observed that the temperature increases the efficiency in both processes and that ETBE is easier treated. On the other hand, it has been analyzed the use of new solvents, in this case ionic liquids, in order to dehydrate fuel oxygenates obtaining satisfactory results. Finally, studies of advanced oxidation processes have been carried out using Fe-zeolites as catalyst. The use of these materials let oxidize MTBE and their most problematic degradation products, like tert-butyl alcohol and tert-butyl formate at environmental conditions and neutral pH in reasonable times.Finally in the fourth and last chapter are summarized the conclusions obtained during the development of this work and the research directions to follow in the future. / En els darrers anys, degut a una creixent preocupació sobre els possibles efectes nocius de les emissions de gasos procedents de l'ús continu de gasolines, la composició d'aquestes ha patit canvis importants. La prohibició dels additius amb plom així com la limitació de compostos aromàtics han donat lloc a una gran expansió arreu del món de l'ús del que es coneixen com additius oxigenats de la gasolina. Aquest compostos son principalment molècules que tenen dins la seva estructura almenys un àtom d'oxigen. Normalment acostumen a ser èters o alcohols. De tots els més utilitzats a nivell mundial son el metil tert butil èter (MTBE), seguit pel etil tert butil èter (ETBE). Aquests compostos degut a les seves propietats físiques i químiques han esdevingut uns contaminants persistents i recalcitrants de les aigues a tot el món.Degut a la problemàtica generada per la contaminació del recursos hídrics és important aprofundir en el coneixement del seu comportament en el medi ambient per tal de obtenir eines que permetin modelitzar i estudiar tant la seva dispersió com la seva remediació. La present tesi doctoral ofereix un estudi termodinàmic important d'aquest compostos i estudia diferents tècniques de remediació.Aquest treball s'estructura en quatre capítols ben diferenciats. El primer d'ells consisteix en una introducció a la problemàtica, la situació actual de la informació física i química de la qual es disposa i de les tècniques existents per al tractament d'aigües contaminades.El segon capítol està enfocat a obtenir i millorar la informació termodinàmica. S'estudia com la temperatura afecta a les interaccions dels additius oxigenats amb diferents constituents de les benzines com son els BTEX(benzè, toluè, etilbenzè i xilens), alcans o compostos de degradació dels oxigenats com pot ser el tert butil alcohol. En aquest capítol s'aporta nova informació termodinàmica prèviament no reportada en la literatura en termes de propietat físiques (densitat i velocitat de so), equilibri vapor líquid i equilibri líquid líquid (en forma de solubilitat en aigua). Com a resultat d'aquest capítol cal remarcar la caracterització de 25 sistemes binaris i els seus compostos purs en termes de propietat física, 3 equilibris binaris líquid vapor i finalment l'estudi de la solubilitat dels èters més utilitzats com additius oxigenats com a funció de la temperatura.El tercer capítol està enfocat des d'un punt de vista tecnològic. En aquest s'estudia termodinàmicament diferent tècniques convencionals per l'eliminació de MTBE i ETBE com son l'adsorció en carbó actiu i l'aireació. S'observa que l'increment de la temperatura augmenta l'eficiència en tot dos processos i que l'ETBE es més fàcilment eliminat. Per altra banda s'ha analitzat l'ús de nous solvents, com son els líquids iònics, per tal de deshidratar additius oxigenats obtenint-se resultats satisfactoris. Finalment s'han realitzat estudis d'oxidació avançada utilitzant zeolites amb contingut fèrric. L'ús d'aquest materials permet oxidar l'MTBE i els seus compostos de degradació més problemàtics, com son el tert butil alcohol i el tert butil formiat en condicions ambientals i pH neutres en temps raonables.Finalment en el quart i últim capítol es resumeixen les conclusions obtingudes durant aquest treball i es donen ressenyes a seguir en investigacions futures en aquest camp.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: zeolite adsorption, TBA, tert butyl alcohol, wastewater remediation. Includes bibliographical references (leaves 60-62 ).