La méthanisation par voie sèche possède différents avantages par rapport à la méthanisation par voie humide. Les réacteurs sont plus petits, les besoins en eau sont moindres, la production de digestat et le prétraitement nécessaire sont également moins importants. Cependant, plusieurs études ont démontré que l'eau favorise l'hydrolyse du substrat et permet le transport des sous-produits d'hydrolyse et des nutriments vers les bactéries. Pour mieux comprendre le rôle de l'eau lors de la méthanisation, des tests de digestion sèche et semi-sèche à partir de substrats organiques complexes (déchets alimentaires, paille de riz, déchets de carotte), avec différentes teneurs en matière sèche de substrat traité ont été réalisées. Les résultats confirment que l'eau joue un rôle essentiel sur le taux de production spécifique de méthane, le rendement final de méthane généré et la dégradation de la matière volatile sèche (MVS). Le rendement final de méthane produit dans des conditions semi-sèches et sèches est respectivement de 51% et de 59% inférieur avec la paille de riz et 4% et 41% de moins pour les déchets alimentaires en comparaison avec des conditions humides. Des tests d'inhibition basés sur l'analyse des acides gras volatils (AGV) ont été menées pour étudier les processus d'inhibition spécifiques qui ont lieu avec les substrats sélectionnés à différentes teneurs en matière sèche. Pour le cas de la méthanisation par voie humide des déchets de carotte, aucune accumulation d'AGV a été trouvé, et toutes les concentrations d'AGV étaient inférieurs aux seuils d'inhibition. Une corrélation directe entre la teneur en matière sèche et la concentration totale d'AGV (AGVtot) a été mise en évidence pour la paille de riz et les déchets alimentaires. Pour la paille de riz, une concentration d'AGVtot maximale de 2,1 g / kg a été trouvé pour la voie sèche, 1 g / kg dans les conditions semi-sèche et 0,2 g / kg dans les conditions humides, alors que pour les déchets alimentaires la concentration d'AGVtot était de 10 g / kg à l'état sec, 9 g / kg dans les conditions semi-sèche et 3 g / kg dans les conditions humides. Un modèle mathématique de la méthanisation de substrats organiques complexes dans des conditions sèches et semi-sèche a été proposé pour simuler l'effet de la teneur en matière sèche sur le processus. Les données obtenues à partir d'expériences en mode batch, en termes de production de méthane et de concentration d'AGV, ont été utilisées pour calibrer le modèle proposé. Les paramètres cinétiques de production et d'élimination d'AGV ont été calibrés à l'aide des données expérimentales, et il a été montré qu'ils sont fortement dépendants de la teneur en matière sèche et différent des valeurs de la littérature concernant la méthanisation par voie humide. Cela est dû à l'accumulation d'AGV dans les conditions sèches, ce qui implique d'utiliser des valeurs plus élevées concernant les constantes d'inhibition introduites dans le modèle. Enfin, comme la méthanisation par voie sèche a généralement lieu dans des réacteurs à écoulement piston, une étude historique et critique de la littérature concernant la compréhension du rôle de l'hydrodynamique dans des bioréacteurs à écoulement piston a été réalisée / Dry Anaerobic Digestion (AD) presents different advantages if compared to wet AD, i.e. smaller reactor size, lesser water addition, digestate production and pretreatment needed, although several studies have demonstrated that water promotes substrate hydrolysis and enables the transfer of process intermediates and nutrients to bacterial sites. To better understand the role of water on AD, dry and semidry digestion tests of selected complex organic substrates (food waste, rice straw, carrot waste), with various TS contents of the treated biomass have been carried out in the present study. The results confirm that water plays an essential role on the specific methane production rate, final methane yield and Volatile Solids (VS) degradation. The final methane yield in semi-dry and dry conditions was 51% and 59% lower for rice straw and 4% and 41% lower for food waste, respectively, if compared with wet conditions. Inhibition tests, based on Volatile Fatty Acid (VFA) analysis, were carried out to investigate the specific inhibition processes that take place with the selected substrates at different TS contents. In wet AD of carrot waste no VFA accumulation was found, and all VFA concentrations were lower than the inhibition limits. A direct correlation between TS content and total VFA (TVFA) concentration was noticed for rice straw and food waste AD. For rice straw a maximum TVFA concentration of 2.1 g/kg was found in dry condition, 1 g/kg in semidry conditions and 0.2 g/kg in wet conditions, whereas for food waste the TVFA concentration was 10 g/kg in dry condition, 9 g/kg in semidry conditions and 3 g/kg in wet conditions. A Mathematical model of complex organic substrate AD in dry and semidry conditions has been proposed to simulate the effect of TS content on the process. The data obtained from batch experiments, in terms of methane production and VFA concentrations, were used to calibrate the proposed model. The kinetic parameters of VFA production and degradation, calibrated using the experimental data, resulted highly dependent on the TS content and different from wet AD literature values. This is due to VFA accumulation in dry conditions, which implies higher values of the inhibition factors introduced in the model. Finally, as dry AD takes usually place in Plug Flow (PF) reactors, an historical and critical review on the role of hydrodynamics in PF bioreactors has been carried out

Dry Anaerobic Digestion (AD) presents different advantages if compared to wet AD, i.e. smaller reactor size, lesser water addition, digestate production and pretreatment needed, although several studies have demonstrated that water promotes substrate hydrolysis and enables the transfer of process intermediates and nutrients to bacterial sites. To better understand the role of water on AD, dry and semidry digestion tests of selected complex organic substrates (food waste, rice straw, carrot waste), with various TS contents of the treated biomass have been carried out in the present study. The results confirm that water plays an essential role on the specific methane production rate, final methane yield and Volatile Solids (VS) degradation. The final methane yield in semi-dry and dry conditions was 51% and 59% lower for rice straw and 4% and 41% lower for food waste, respectively, if compared with wet conditions. Inhibition tests, based on Volatile Fatty Acid (VFA) analysis, were carried out to investigate the specific inhibition processes that take place with the selected substrates at different TS contents. In wet AD of carrot waste no VFA accumulation was found, and all VFA concentrations were lower than the inhibition limits. A direct correlation between TS content and total VFA (TVFA) concentration was noticed for rice straw and food waste AD. For rice straw a maximum TVFA concentration of 2.1 g/kg was found in dry condition, 1 g/kg in semidry conditions and 0.2 g/kg in wet conditions, whereas for food waste the TVFA concentration was 10 g/kg in dry condition, 9 g/kg in semidry conditions and 3 g/kg in wet conditions. A Mathematical model of complex organic substrate AD in dry and semidry conditions has been proposed to simulate the effect of TS content on the process. The data obtained from batch experiments, in terms of methane production and VFA concentrations, were used to calibrate the proposed model. The kinetic parameters of VFA production and degradation, calibrated using the experimental data, resulted highly dependent on the TS content and different from wet AD literature values. This is due to VFA accumulation in dry conditions, which implies higher values of the inhibition factors introduced in the model. Finally, as dry AD takes usually place in Plug Flow (PF) reactors, an historical and critical review on the role of hydrodynamics in PF bioreactors has been carried out

For enhancing anaerobic sludge digestion and biogas recovery, an increase in organic load rate (OLR) from 1.0 to 3.0kgVS/(m3·day) was imposed upon a new anaerobic digestion process combined with a sludge recirculation. The new setup requires a traditional mesophilic anaerobic digester coupled with a centrifuge for maintaining relatively high solid content within the digester. The hypothesis of this study was that increasing continuously OLR from 1.0 to 3.0kgVS/(m3·day) in a pilot-scale anaerobic digester with recycled sludge would not badly influence the digester stability, based on which biogas production would be enhanced. To test this hypothesis, a continuous 73-day study with laboratory experiment was conducted. Due to scarcity of original feeding sludge and its deteriorating quality, OLR had to be increased relied on introduction of extra sludge followed by measurement of total solid (TS) and volatile solid (VS) contents in both feeding sludge and digester sludge, for calculating OLR and examining its variations. To assess the relationship between biogas production and OLR, a measurement of gas yield and methane content was a necessity, performed by applying a biogas flow meter and MSA AUER EX-METER II (P). Moreover, temperature, pH value, volatile fatty acid (VFA) and alkalinity must be tested frequently, for the purpose of preventing system failure. The results demonstrate that the digester succeeded in withstanding an OLR up to 3.15kgVS/(m3·day). Furthermore, an enhancement in biogas yield and methane content were observed after increasing the OLR by introducing extra sludge. Biogas production measurement performed during this study indicated that biogas yield was enhanced by 73%, with a maximum production of 14.5m3/day, when OLR was increased from 2.05 to 3.15kgVS/(m3·day). However, methane content was merely promoted by 10.5%, to the highest value of 63%, with the same increase in OLR. Specific gas production (SGP), as another means of evaluating the relationship between biogas production and OLR, was observed to be 0.65Nm3/kg VSin averagely.

Made available in DSpace on 2014-07-29T14:39:37Z (GMT). No. of bitstreams: 1 Dissertacao Celso de Carvalho Braga.pdf: 3312309 bytes, checksum: f978b2519d34cde7af31bff47e8526ea (MD5) Previous issue date: 2012-03-01 / The construction of reservoirs for hydroelectric generates various environmental impacts, for instance, changes in the displacement and the concentration of suspended solids, thus causing changes in the fauna and flora of the water. The survey of suspended solids in a determined watershed is important to make correct decisions regarding the planning for a bowl, because the amount of solids is directly related to the land use. The problems caused by suspended solids include erosion, transport, deposition and compaction, in addition the suspended solids impair the quality of water for human consumption. This study aimed to analyze the spatial and temporal distribution of the concentration of suspended solids (CSS) in the main source of the lake in Barra dos Coqueiros and its influence on the life cycle of the reservoir from March 2011 to August 2011. To achieve the proposed goals, it was used methods such as calculating the concentration of suspended solids according to the proposal of Wetzel and Likens (1991), checking the levels of turbidity and water clarity in accordance with the proposal to Esteves (1998) and Tundisi (2008), calculating the flow of the sources of water by the method of floats as proposed by Ramos and Oliveira (2003), Palhares (2007), and calculating the total solid discharge of the main sources of water (of the) using simplified method of Colby (1964) that takes into consideration: liquid discharge, average speed, average depth, width and cross section measured concentration of suspended solids. According to the data, we reached the following conclusion: the concentration of suspended solids is well related to the data turbidity and water transparency. In the data collection reservoir of the rainy season, the concentration of suspended solids ranged from 7,5 to 30,5 mgL-1 and greater than the collection of the dry period, which ranged from 0,25 to 7,5 mgL-1. The same thing happens to the water transparency using a Secchi disk that ranged from 0,16 to 0,30 meters in the rainy season and 1,40 to 3,50 meters in the dry season. As for turbidity, the indices found shows that the reflectance of light in a rainy period ranged from 51 to 72 NTU, whereas the dry period ranged from 0 to 3,7 NTU. According to the evaluation of the spatial and temporal distribution of suspended solids concentration of the main sources of water in the reservoir of Barra dos Coqueiros, the main lake stands out among the sources analyzed, due to the higher concentration of suspended solids, ranging from 2,5 mgL-1 in the dry season to 14,5 mgL-1 in the rainy season. / A construção de reservatórios para usinas hidrelétricas geram impactos ambientais diversos, como, por exemplo, mudanças no deslocamento e concentração de sólidos em suspensão, ocasionando assim mudanças na fauna e flora aquáticas. O estudo dos sólidos em suspensão de uma determinada bacia hidrográfica é importante para que se possam tomar decisões corretas quanto ao planejamento de atividades de uma bacia, pois a quantidade de sólidos está diretamente associada ao uso da terra. Os problemas gerados pelos sólidos em suspensão vão desde a erosão, transporte, deposição e compactação, além de que os sólidos em suspensão prejudicam a qualidade da água para o consumo humano. O presente trabalho teve por objetivo analisar a distribuição espacial e temporal da concentração de sólidos em suspensão (CSS) nos principais afluentes e lago da UHE Barra dos Coqueiros, e sua influência na vida útil do reservatório no período de março a agosto de 2011. Os métodos utilizados para alcançar os objetivos propostos foram: calcular a concentração de sólidos em suspensão de acordo com a proposta de WETZEL E LIKENS (1991), verificar os níveis de turbidez e transparência da água de acordo com a proposta de ESTEVES (1998) e TUNDISI (2008), calcular a vazão dos afluentes pelo método de flutuadores, de acordo com a proposta de RAMOS e OLIVEIRA (2003), PALHARES (2007), e calcular a descarga sólida total dos principais afluentes pelo método simplificado de COLBY (1964) que leva em consideração: descarga líquida, velocidade média, profundidade média, largura da seção transversal e concentração medida de sólidos em suspensão. De acordo com os dados obtidos, chegou-se à seguinte conclusão: que a concentração de sólidos em suspensão tem boa relação com os dados de turbidez e transparência da água. Na coleta de dados do reservatório do período chuvoso, a concentração de sólidos em suspensão variou de 7,5 a 30,5 mgL-1, sendo maior que na coleta do período seco, que variou de 0,25 a 7,5 mgL-1. O mesmo acontece com transparência de água utilizando o disco de Secchi que variou de 0,16 a 0,30 metros no período chuvoso e de 1,40 a 3,50 metros no período seco. Quanto à turbidez, os índices encontrados mostram que a refletância da luz no período chuvoso variou de 51 a 72 NTU, enquanto no período seco variou de 0 a 3,7 NTU. Quanto à avaliação da distribuição espacial e temporal da concentração de sólidos em suspensão dos principais afluentes do reservatório da UHE Barra dos Coqueiros o Córrego Matriz se destaca entre os afluentes analisados, por apresentar maiores concentrações de sólidos em suspensão, variando de 2,5 mgL-1 no período seco a 14,5 mgL-1 no período chuvoso.