Impacts of Ethanol in Gasoline on Subsurface Contamination

The increasing use of ethanol as a gasoline additive has raised concerns over the potential impacts ethanol might have on groundwater contamination. In North America, 10% ethanol is commonly being added to gasoline (termed E10). Ethanol is usually denaturated with gasoline compounds before being transported; consequently E95 (95% ethanol) mixtures are also common. Therefore, spills with compositions ranging from E10 to E95 can be anticipated. The compounds of main concern associated with gasoline spills are benzene, toluene, ethylbenzene and xylenes (BTEX), trimethylbenzenes (TMBs) and naphthalene, due to their higher mobility and potential risks to human health. Ethanol is thought to increase mobility of the NAPL, create higher hydrocarbon concentrations in groundwater due to cosolvency, and decrease the rate of gasoline hydrocarbon biodegradation, with consequent increase in the length of the dissolved plumes. The objective of this research was to improve the knowledge about ethanol fate in the subsurface and the impacts it might have on the fate of gasoline compounds. To investigate that, laboratory experiments and controlled field tests supported by numerical modeling were conducted. To evaluate the impact of ethanol on dissolved hydrocarbon plumes, data from a controlled field test were evaluated using a numerical model. The mass discharge of BTEX, TMB and naphthalene from three sources (E0, E10 and E95) emplaced below the water table was compared to simulation results obtained in the numerical model BIONAPL/3D. It was shown that if ethanol fuel mixtures get below the water table, ethanol is dissolved and travels downgradient fast, in a short slug. Mass discharge from the E0 and E10 sources had similar hydrocarbon decay rates, indicating that ethanol from E10 had no impact on hydrocarbon degradation. In contrast, the estimated hydrocarbon decay rates were significantly lower when the source was E95. The aquifer did not have enough oxygen to support the mass loss observed assuming complete mineralization. Assuming a heterogeneous distribution of hydraulic conductivity did little to overcome this discrepancy. A better match between the numerical model and the field data was obtained assuming partial degradation of hydrocarbons to intermediate compounds, with consequent less demand for oxygen. Besides depending on the concentration of ethanol in the groundwater, the impact of ethanol on hydrocarbon degradation appears to be highly dependent on the aquifer conditions, such as availability of electron acceptors and adaptation of the microbial community. Another concern related to ethanol biodegradation is formation of explosive levels of methane. In this study, methane δ13C from toluene and ethanol as substrates was evaluated in microcosm tests. It was shown that methane is enriched in δ13C when ethanol is the substrate. Ethanol derived methane δ13C is in the range of -20‰ to 30‰, while methane from gasoline is around -55‰. The different ranges of δ13C allow it to be used as a tool to identify methane’s origin. This tool was applied to seven ethanol-gasoline contaminated sites. Methane origin could be clearly distinguished in five of the seven sites, while in the other two sites methane appears to have been produced from both ethanol and gasoline. Both ethanol and gasoline were identified as the source of methane in hazardous concentrations. The behaviour of ethanol fuels in the unsaturated zone was evaluated in 2-dimensional (2-D) lab tests and in a controlled field test. In the 2-D lab tests, dyed gasoline and ethanol were injected in the unsaturated zone simulated in a transparent plexiglass box packed with glass beads. Tests were performed under both static conditions and with horizontal groundwater flow. It was confirmed that some ethanol can be retained in the unsaturated zone pore water. However, most of the ethanol went through the unsaturated zone and reached the pre-existing gasoline pool. Ethanol displaced the NAPL to deeper positions, and it was shown that for large ethanol releases much of the gasoline can be displaced to below the water table. The ethanol that reaches the capillary fringe was shown to travel downgradient rapidly at the top of the capillary fringe, while ethanol was also retained in the unsaturated zone. The behaviour of ethanol fuel spills was further evaluated in a controlled field test. 200L of E10 containing around 5% MTBE was released into the unsaturated zone. Groundwater concentrations of ethanol, MTBE, BTEX, TMB and naphthalene above and below the water table were monitored downgradient of the source in multilevel wells. Lab tests were performed to evaluate the applicability of these samplers for volatile organic compounds. It was shown that volatilization losses might be significant when bubbles formation in the sampling line could not be avoided. A method for losses estimation and correction of the concentrations was developed. Concentrations in the source zone were measured in soil samples. Despite the thin (35 cm) unsaturated zone at the site, most of the ethanol was retained in the unsaturated zone pore water, above the capillary fringe. Being in zones of low effective hydraulic conductivity, ethanol was not transported downgradient, and remained in the unsaturated zone for more than 100 days. Ethanol mass discharge was much lower than would be anticipated based solely on the ethanol fraction in the gasoline and on its solubility. Oscillations in the water table, particularly when a shallow position was maintained for prolonged periods, flushed some ethanol to zones with high water saturation, where horizontal transport occurred. The ethanol that reaches the saturated zone appears in the downgradient wells as a slug, with relatively low concentrations. No effect of ethanol on gasoline hydrocarbons was observed, a consequence of most of the ethanol being retained in the unsaturated zone. In summary, spills of ethanol fuels might have two different outcomes, depending on whether most of the ethanol is retained in the unsaturated zone or if most reaches the capillary fringe and the saturated zone. The relation between the ethanol volume spilled and the retention capacity of the unsaturated zone will control the spill behaviour. The volume of ethanol that can be retained in the unsaturated zone is a function of the volume of water that is contacted by the infiltrating NAPL. Therefore, the type of soil, heterogeneities, depth to the water table and area of the spill will be determinant factors. If a relatively large volume of ethanol reaches the capillary fringe, ethanol will travel rapidly in the groundwater possibly in high concentrations, potentially enhancing dissolved hydrocarbon plumes. However, when most of the ethanol is retained in the unsaturated zone, it will likely be detected downgradient only in low concentration, and in pulses spread in time. In this scenario, impact on hydrocarbon plumes will be minor

Technical and economical feasibility of coagulant recovery from water treatment plant sludges.

Esse trabalho teve como objetivo avaliar a viabilidade técnica e econômica da regeneração de coagulantes a partir do lodos gerados em ETA\'s. Foi considerado que o coagulante regenerado será empregado em sistemas de tratamento de esgotos. A regeneração de coagulante consiste basicamente em promover uma alteração no pH do lodo, de forma que os hidróxidos metálicos presentes são solubilizados. A fase líquida com alta concentração de metais é então separada, constituindo o coagulante regenerado. Consequentemente, essa tecnologia propicia a recuperação de um recurso, que é o coagulante, e a redução de lodo. Para a verificação da viabilidade técnica foram realizados ensaios de acidificação em escala de bancada com lodos das ETA\'s Guaraú e Rio Grande, visando o estudo das condições de regeneração, da qualidade do coagulante produzido e do lodo restante. Foi verificado que do ponto de vista técnico a regeneração de coagulantes é uma alternativa possível, gerando um coagulante aproximadamente 100 vezes mais diluído que os comerciais, mas com desempenho satisfatório na aplicação no tratamento de efluentes de reator UASB. As reduções médias de sólidos em suspensão nos lodos utilizados foram de 28% e 53%. A avaliação econômica foi realizada considerando uma ETA com características similares à ETA Rio Grande, com um sistema de regeneração em funcionamento. Foi verificado que considerando as reduções de custos decorrentes da diminuição de lodo a ser tratado e disposto, o custo de produção do coagulante regenerado é muito próximo ao custo do coagulante comercial. Portanto, conclui-se que hoje em dia essa tecnologia deve ser considerada como uma alternativa potencialmente viável dos pontos de vista técnico e econômico para o tratamento e reaproveitamento de lodo de ETA\'s.The primary goal of this work was to evaluate the technical and economical feasibility of coagulant recovery from water treatment plant sludges, considering that the recovered coagulant is going to be used in wastewater treatment plants. The coagulant recovery technology consists in change the sludge pH, in order to solubilize the present metal hydroxides. The liquid phase with high metals concentrations is then separated, becoming the recovered coagulant. This technology provides a resource recovery, which is the coagulant, and also a reduction in the amount of sludge that needs to be treated and disposed. To verify the technical feasibility, acidification bench tests were conduced using sludges from Guaraú e Rio Grande water treatment plants, in order to study the regeneration conditions, the recovered coagulant quality and the remaining sludge. From the technical point of view, it was verified that coagulant recovery is a possible alternative, producing a coagulant 100 times more diluted than the commercial coagulant, but with a satisfactory behavior in the treatment of UASB reactor effluent. The suspended solids average reductions in the Rio Grande and Guaraú water treatment plants sludges were 53% and 28%, respectively. The economical evaluation was done using the results obtained in the bench tests and considering a water treatment plant similar to Rio Grande. It was verified that considering the costs decrease due to the sludge reduction, the recovered coagulant production cost was very similar to commercial coagulants cost. Thus, it was concluded that nowadays this technology must be considered as a potential alternative for the treatment and reuse for water treatment plant sludges, regarding to the technical and economical aspects

Technical and economical feasibility of coagulant recovery from water treatment plant sludges.

Esse trabalho teve como objetivo avaliar a viabilidade técnica e econômica da regeneração de coagulantes a partir do lodos gerados em ETA\'s. Foi considerado que o coagulante regenerado será empregado em sistemas de tratamento de esgotos. A regeneração de coagulante consiste basicamente em promover uma alteração no pH do lodo, de forma que os hidróxidos metálicos presentes são solubilizados. A fase líquida com alta concentração de metais é então separada, constituindo o coagulante regenerado. Consequentemente, essa tecnologia propicia a recuperação de um recurso, que é o coagulante, e a redução de lodo. Para a verificação da viabilidade técnica foram realizados ensaios de acidificação em escala de bancada com lodos das ETA\'s Guaraú e Rio Grande, visando o estudo das condições de regeneração, da qualidade do coagulante produzido e do lodo restante. Foi verificado que do ponto de vista técnico a regeneração de coagulantes é uma alternativa possível, gerando um coagulante aproximadamente 100 vezes mais diluído que os comerciais, mas com desempenho satisfatório na aplicação no tratamento de efluentes de reator UASB. As reduções médias de sólidos em suspensão nos lodos utilizados foram de 28% e 53%. A avaliação econômica foi realizada considerando uma ETA com características similares à ETA Rio Grande, com um sistema de regeneração em funcionamento. Foi verificado que considerando as reduções de custos decorrentes da diminuição de lodo a ser tratado e disposto, o custo de produção do coagulante regenerado é muito próximo ao custo do coagulante comercial. Portanto, conclui-se que hoje em dia essa tecnologia deve ser considerada como uma alternativa potencialmente viável dos pontos de vista técnico e econômico para o tratamento e reaproveitamento de lodo de ETA\'s.The primary goal of this work was to evaluate the technical and economical feasibility of coagulant recovery from water treatment plant sludges, considering that the recovered coagulant is going to be used in wastewater treatment plants. The coagulant recovery technology consists in change the sludge pH, in order to solubilize the present metal hydroxides. The liquid phase with high metals concentrations is then separated, becoming the recovered coagulant. This technology provides a resource recovery, which is the coagulant, and also a reduction in the amount of sludge that needs to be treated and disposed. To verify the technical feasibility, acidification bench tests were conduced using sludges from Guaraú e Rio Grande water treatment plants, in order to study the regeneration conditions, the recovered coagulant quality and the remaining sludge. From the technical point of view, it was verified that coagulant recovery is a possible alternative, producing a coagulant 100 times more diluted than the commercial coagulant, but with a satisfactory behavior in the treatment of UASB reactor effluent. The suspended solids average reductions in the Rio Grande and Guaraú water treatment plants sludges were 53% and 28%, respectively. The economical evaluation was done using the results obtained in the bench tests and considering a water treatment plant similar to Rio Grande. It was verified that considering the costs decrease due to the sludge reduction, the recovered coagulant production cost was very similar to commercial coagulants cost. Thus, it was concluded that nowadays this technology must be considered as a potential alternative for the treatment and reuse for water treatment plant sludges, regarding to the technical and economical aspects

What Makes Risk Communication Efficient? The Stakeholder View

Abstract Environmental risk communication comprises an essential step in contaminated sites management, being one of its basic principles. However, there are few studies and technical guidelines on how to perform risk communication. This research aimed to identify the main factors that can contribute to efficient risk communication from the stakeholders’ perspective: those affected or potentially affected by the risks, representatives of institutions responsible for risk communication, environmental agencies, and consultants. To achieve that, the Q technique, a methodology specialized in the study of people and their subjectivities, was applied to 24 individuals. Five factors representing the stakeholders’ perspectives were identified: 1 - Trust; 2 - Secure communication; 3 - Dialogue; 4 - Partnership; and 5 - Health, in addition to a set of consensual information between all groups. Concern for the health of those involved was the most important point of view for most participants