Orientador: Antonio Roberto Balbo / Coorientadora: Célia Aparecida dos Reis / Banca: Marcelo Suetake / Banca: André Christovão Pio Martins / Resumo: Atualmente pesquisas sobre a produção de energia com menor impacto ambiental, com maior rendimento energético e, possivelmente, a um custo mínimo de produção, são de interesse mundial. Desta forma, a produção de energia renovável, com estas características, através de biodigestores torna-se uma alternativa relevante. Os biodigestores, em geral, consistem de biorreator que armazena matéria orgânica fresca (substrato ou biomassa) de origem humana, animal ou vegetal. A fermentação anaeróbica destes substratos produz um gás combustível (biogás) que pode ser utilizado como fonte de energia e o material remanescente no biodigestor pode ser usado como biofertilizante. O processo de biodigestão é complexo, pois envolve vários grupos de bactérias e o seu entendimento é importante para promoção de agentes que visam aumentar a eficiência dos biodigestores. Neste trabalho propõe-se um modelo dinâmico não linear para descrever o processo de fermentação da biomassa dentro do biodigestor. Realiza-se também uma análise do modelo mediante a técnica de Lyapunov, a qual possibilitou a investigação de soluções analíticas assintoticamente estáveis e um estudo de seu espaço de fase, que contempla a sua estabilidade assintótica. Simulações numéricas são realizadas para a validação dos resultados obtidos ao modelo proposto / Abstract: Nowadays, research on energy production with lower environmental impact, with higher energy efficiency and, possibly, at a minimum cost of production, is of worldwide interest. In this way, the production of renewable energy, with these characteristics, through biodigesters becomes a relevant alternative. Biodigesters generally consist of a chamber that stores fresh organic matter (substrate or biomass) of human, animal or plant origin. Anaerobic fermentation of these substrates produces a fuel gas (biogas) that can be used as an energy source and the remaining material in the biodigester can be used as biofertilizer. The biodigestion process is complex because it involves several groups of bacteria and its understanding is important to promote agents that aim to increase the efficiency of biodigesters. This essay proposes a dynamic non-linear model to describe the fermentation process of an Indian biodigester. It is also proposed an analysis of the model using the Lyapunov technique, which became possible the investigation of asymptotically stable analytical solutions and asymptotic stability and a study of its phase space, which contemplates its asymptotic stability. Numerical simulations are performed to convalidate the proposed model. / Mestre

Anaerobic digestion (AD) is a biochemical process consisting of the microbiological conversion of organic materials for the purpose of generating biogas. Biogas is typically composed of 50 to 70% methane (CH4) and 50 to 30% carbon dioxide (CO2) with trace amounts of other compounds. Anaerobic digestion technology is a bioprocessing technology that has the potential to be integrated into an ethanol facility to further capture energy, in the form of methane gas, for use in a combined heat and power (CHP) generator or for integration into the natural gas pipeline grid after undergoing an upgrading process. The most simplistic design of an AD system is the solid state digester (SSD) which is able to process very high solids content materials (greater than 15% solids). A SSD has the potential to be utilized as a manure management system in a beef cattle feedlot and it has the potential to integrate seamlessly into a combined ethanol- feedlot operation to capitalize on the eco-cluster concept in bioenergy production. This thesis investigates the biogas and digestate composition seen from four material blends in a solid-state digester (SSD) system operated as a batch reactor. Wet distiller grains (WDG) from a grain ethanol process and cattle manure were the substrates investigated. To assess the biogas composition the system was operated over a period of time to achieve a quasi steady state within the microbial population to maximize the CH4 concentration in the biogas composition. To assess the robustness of the microbial population within each substrate blend, the biogas concentrations were measured over three cycle periods where a portion of the used substrate was replaced with an equal amount of fresh substrate. The digestate composition was analyzed at the end of each of the cycles and compared with the raw substrate to determine changes in solids and nutrient values. The biogas production calculated in this study determined 0.17, 0.21, 0.18, and 0.12L per gram (VS) within 100% WDG, 75%WDG and 25% manure, 25% WDG and 75% manure and the 100% manure substrate (Group 1 through 4) respectively, averaged over all three digestion cycles. At the end of three cycles of digestion the biogas within the substrate blend containing 25% WDG and 75% manure (Group 3) achieved a measured CH4 concentration of 49% and the biogas within the 100% manure substrate (Group 4) achieved a 59% concentration of CH4. The duration for each of Group 3 and Group 4 to achieve the production of viable biogas was 100 and 90 days of operation respectively. Thus it can be concluded that a SSD system start up duration will be between three and four months in duration. The gas data gathered in this research study indicates Group 3 had the most robust methanogenic culture established as it has the lowest overall N2 and CO2 concentration detected in the biogas, and the most consistent performance of CH4 production during each cycle. The investigation conducted on the nutrient data gathered in this research supports the conclusion drawn from the gas data regarding the overall methanogenic performance of the substrate blends. The nutrient data for Group 3 maintained an average carbon to nitrogen (C:N) ratio of 25:1 over all three digestion cycles. The nitrogen, phosphorous, potassium, and sulphur components of the manure fertilizer value were maintained through the digestion process of this investigation thus typical manure application rate calculations are applicable when field applying digestate.

Anaerobic digestion (AD) is a biochemical process consisting of the microbiological conversion of organic materials for the purpose of generating biogas. Biogas is typically composed of 50 to 70% methane (CH4) and 50 to 30% carbon dioxide (CO2) with trace amounts of other compounds. Anaerobic digestion technology is a bioprocessing technology that has the potential to be integrated into an ethanol facility to further capture energy, in the form of methane gas, for use in a combined heat and power (CHP) generator or for integration into the natural gas pipeline grid after undergoing an upgrading process. The most simplistic design of an AD system is the solid state digester (SSD) which is able to process very high solids content materials (greater than 15% solids). A SSD has the potential to be utilized as a manure management system in a beef cattle feedlot and it has the potential to integrate seamlessly into a combined ethanol- feedlot operation to capitalize on the eco-cluster concept in bioenergy production. This thesis investigates the biogas and digestate composition seen from four material blends in a solid-state digester (SSD) system operated as a batch reactor. Wet distiller grains (WDG) from a grain ethanol process and cattle manure were the substrates investigated. To assess the biogas composition the system was operated over a period of time to achieve a quasi steady state within the microbial population to maximize the CH4 concentration in the biogas composition. To assess the robustness of the microbial population within each substrate blend, the biogas concentrations were measured over three cycle periods where a portion of the used substrate was replaced with an equal amount of fresh substrate. The digestate composition was analyzed at the end of each of the cycles and compared with the raw substrate to determine changes in solids and nutrient values. The biogas production calculated in this study determined 0.17, 0.21, 0.18, and 0.12L per gram (VS) within 100% WDG, 75%WDG and 25% manure, 25% WDG and 75% manure and the 100% manure substrate (Group 1 through 4) respectively, averaged over all three digestion cycles. At the end of three cycles of digestion the biogas within the substrate blend containing 25% WDG and 75% manure (Group 3) achieved a measured CH4 concentration of 49% and the biogas within the 100% manure substrate (Group 4) achieved a 59% concentration of CH4. The duration for each of Group 3 and Group 4 to achieve the production of viable biogas was 100 and 90 days of operation respectively. Thus it can be concluded that a SSD system start up duration will be between three and four months in duration. The gas data gathered in this research study indicates Group 3 had the most robust methanogenic culture established as it has the lowest overall N2 and CO2 concentration detected in the biogas, and the most consistent performance of CH4 production during each cycle. The investigation conducted on the nutrient data gathered in this research supports the conclusion drawn from the gas data regarding the overall methanogenic performance of the substrate blends. The nutrient data for Group 3 maintained an average carbon to nitrogen (C:N) ratio of 25:1 over all three digestion cycles. The nitrogen, phosphorous, potassium, and sulphur components of the manure fertilizer value were maintained through the digestion process of this investigation thus typical manure application rate calculations are applicable when field applying digestate.

El consum energètic representa un 30 % dels costos d'operació en sistemes intensius de tractament d'aigües residuals urbanes. En depuradores convencionals que utilitzin un sistema de fangs activats, entorn al 15-20 % de l'energia és consumida en la línia dels fangs, que inclou el bombeig, l'espessiment, l'estabilització i la deshidratació. Per tant, la optimització de la gestió dels fangs pot contribuir substancialment en la reducció dels costos de tractament d'aigües residuals. La digestió anaeròbia termofílica és més eficient que la mesofílica i pscicrofílica, en termes de producció de biogàs i metà, eliminació de sòlids volàtils (SV) i destrucció de patògens. El procés es pot accelerar mitjançant el pre¬tractament dels fangs, afavorint la seva solubilització i hidròlisi. L'objecte d'aquesta Tesi Doctoral fou estudiar l'impacte dels paràmetres del procés en la digestió anaeròbia termofílica dels fangs de depuradora urbana, avaluar l'efecte del pre-tractament tèrmic dels fangs a baixa temperatura, i valorar processos alternatius des del punt de vista energètic. Els resultats experimentals presentats s'obtingueren mitjançant l'operació de dos reactors de laboratori durant prop de dos anys. En aquest període es va estudiar l'efecte de la temperatura del procés, del temps de retenció dels fangs (TRF), de la velocitat de càrrega orgànica (VCO) i del pre-tractament a 70 ºC en la digestió anaeròbia dels fangs de depuradora. El procés fou avaluat en termes de la producció d'energia (biogàs i metà) i de la qualitat del fang digerit (contingut de SV i d'àcids grassos volàtils (AGV), facilitat de deshidratació i higienització). S'analitzà l'estabilitat del procés a mesura que es reduïa el TRF i s'incrementava la VCO, i es comparà l'eficiència en períodes d'estabilitat corresponents a les diferents condicions operacionals. Finalment, s'avaluaren els resultats des del punt de vista energètic, mitjançant el càlcul de balanços i ratis energètics teòrics, que es compararen amb els resultats obtinguts a partir de dades experimentals d'altres estudis. També s'utilitzà un model cinètic de primer ordre. Les conclusions que es desprenen d'aquest treball es resumeixen a continuació: Durant la digestió anaeròbia dels fangs, la transició d'un reactor mesophilic (43 ºC) a termofílic (50 ºC) es podria dur a terme sense alterar el procés, treballant a TRF elevats (≥ 30 dies) i VCO baixes (≤ 0.5 kg SV m-3reactor d-1). En aquestes condicions, les principals diferències entre reactors termofílics (50-55 ºC) i mesofílics (38-43 ºC) fan referència a una certa acumulació d'AGV (0.5-2.5 g L-1) i millora de la destrucció de patògens (E. coli ≤ 102 UFC mL-1). La digestió termofílica a 50 ºC i 55 ºC dóna lloc a resultats similars pel que fa a la producció de biogàs, estabilització, higienització i facilitat de deshidratació de l'efluent, si no varien els altres paràmetres operacionals. La producció de metà tendeix a incrementar proporcionalment a la VCO, és a dir al TRF i el contingut de SV als fangs alimentats. Així mateix, la qualitat de l'efluent (contingut de SV i AGV, facilitat de deshidratació dels fangs) també depèn de la VCO. D'acord amb els resultats obtinguts a 55 ºC, la producció de metà s'incrementà 2-3 vegades (de 0.2 a 0.4-0.6 m3CH4 m3reactor d-1) en disminuir el TRF de 30 a 15-10 dies, incrementant la VCO de 0.5 a 2.5-3.5 kg SV m3reactor d-1. En canvi, el procés es desestabilitzà amb la reducció del TRF a 6 dies i VCO per sobre de 5 kg SV m3reactor d-1. Les següents concentracions poden ser útils per detectar i prevenir la desestabilització d'un digestor termofílic de fangs: AGV totals (2.5 g L-1), acetat (0.5 g L-1), rati acetat/propionat (0.5), alcalinitat intermèdia (1.8 g CaCO3 L-1), rati alcalinitat intermèdia/alcalinitat parcial (0.9), rati alcalinitat intermèdia/alcalinitat total (0.5), contingut de metà al biogàs (55 %). El pre-tractament a 70 ºC afavoreix la solubilització dels fangs, incrementant la proporció de matèria orgànica soluble respecte la matèria orgànica total del 5 % al 50 % en 9-24 h; seguit d'una progressiva generació d'AGV després de 24h. Durant la subseqüent digestió anaeròbia de fangs pre¬tractats (9-48 h), s'incremetà la producció de biogàs en un 30-40 %, treballant a 55 ºC i 10 dies de TRF. El rendiment de producció de biogàs fou un 30 % superior amb fangs pre-tractats (0.28-0.30 vs. 0.22 L·gVS¬1) i el contingut de metà al biogàs també fou superior (69 % vs. 64 %). La digestió anaeròbia termofílica de fangs pot donar lloc a una producció neta d'energia, durant estacions fredes i càlides, si s'utilitzen reactors amb aïllament tèrmic de les parets i amb recuperació energètica a partir del biogàs i dels fangs digerits. En aquest cas, l'eficiència energètica de reactors termofílics treballant a la meitat de TRF (10-15 dies) que reactors mesofílics (20-30 dies) seria similar, per la qual cosa el cabal diari podria ser doblat, o el volum del reactor reduït, amb el conseqüent estalvi en el cost de tractament dels fangs. A més, un sistema en dues etapes (70/55 ºC) produiria més energia neta que un sistema en una sola etapa (55 ºC) amb un TRF de 10 dies. De totes maneres, la quantitat d'energia neta generada augmenta amb el volum del digestor donat que, malgrat la disminució en la producció de metà a TRF creixents, la producció d'energia segueix essent superior al consum, i per tant com més quantitat de fangs hi hagi al digestor, més energia es produirà. / Energy consumption accounts for some 30 % of the total operating costs of intensive sewage treatment systems. In conventional wastewater treatment plants employing an activated sludge process, around 15-20 % of this energy is used in the sludge treatment line, including sludge pumping, thickening, stabilisation and dewatering. Therefore, optimisation of sludge management can substantially contribute in the reduction of wastewater treatment costs. Thermophilic anaerobic digestion is more efficient than mesophilic anaerobic digestion, in terms of biogas production, volatile solids (VS) removal and pathogens destruction. The process might be further accelerated by sludge pre-treatment, promoting sludge solubilization and hydrolysis. The aim of this PhD Thesis was to study the impact of process parameters on the thermophilic anaerobic digestion of sewage sludge, to evaluate the effect of implementing a low temperature pre¬treatment step, and to assess alternative processes from an energy perspective. The experimental results presented were obtained by operating two lab-scale reactors for almost two years. During this period, the effect of process temperature, sludge retention time (SRT), organic loading rate (OLR) and 70 ºC sludge pre-treatment on the anaerobic digestion of sewage sludge was studied. The process was evaluated in terms of energy production (i.e. biogas and methane production) and the quality of the effluent sludge (i.e. VS and volatile fatty acids (VFA) content, sludge dewaterability and hygienisation). Focus was put on the stability of the process at decreasing SRT and increasing OLR. Process efficiency during stable performance under each operating condition assayed was compared. Finally, the results were assessed from an energy perspective, by means of theoretical energy balances and ratios; and compared to the results obtained with experimental data from other studies. A first order kinetic model was also used. The conclusions drawn from the different issues dealt in this work are summarised as follows: During anaerobic sludge digestion, the transition from a mesophilic (43 ºC) to a thermophilic operation (50 ºC) may be carried out without disturbing the process, by operating the reactors at high SRT ( ≥ 30 days) and low OLR (≤ 0.5 kg VS m-3reactor d-1). Under such conditions, some VFA accumulation (0.5-2.5 g L-1) and enhanced pathogen destruction (residual E. coli ≤ 102 CFU mL-1) would be the main differences of thermophilic (50-55 ºC) compared to mesophilic (38-43 ºC) reactors. Thermophilic sludge digestion at 50 ºC and 55 ºC should be similar in terms of biogas production and effluent stabilisation, hygienisation and dewaterability; provided that other process parameters are the same. Methane production rate tends to increase proportionally to the OLR, thus to the SRT and VS concentration in the feed sludge. Similarly, the quality of the effluent sludge (VS content, VFA content and sludge dewaterability) is also affected by the OLR. According to the results obtained at 55 ºC, methane production rate increased by 2-3 times (from 0.2 to 0.4-0.6 m3CH4 m3reactor d-1) by decreasing the SRT from 30 to 15-10 days; increasing the OLR from 0.5 to 2.5-3.5 kg VS m3reactor d-1. However, process unbalance resulted from SRT reduction to 6 days, with OLR above 5 kg VS m3reactor d-1. The following concentrations might be useful to detect and prevent digester failure during thermophilic sludge digestion: total VFA (2.5 g L-1), acetate (0.5 g L-1), acetate/propionate ratio (0.5), intermediate alkalinity (1.8 g CaCO3 L-1), intermediate alkalinity/partial alkalinity ratio (0.9), intermediate alkalinity/total alkalinity ratio (0.5), methane content in biogas (55 %). The 70 ºC sludge pre-treatment may initially promote sludge solubilization, increasing the concentration of soluble to total organic matter from 5 to 50 % within 9-24 h; which is followed by a progressive VFA generation after 24 h. Subsequent anaerobic digestion of pre-treated sludge samples (9¬48 h) could increase biogas production by 30-40 % working at 55 ºC with a SRT of 10 days. Biogas yield is some 30 % higher with pre-treated sludge (0.28-0.30 vs. 0.22 L·gVSfed-1) and methane content in biogas is also higher with pre-treated sludge (69 vs. 64 %). Thermophilic anaerobic sludge digestion would result in net energy production, during cold and warm seasons, provided that digesters with wall insulation and with energy recovery from both the biogas produced and the effluent sludge are used. In this case, the energetic efficiency would be similar for thermophilic digesters working at half the SRT (10-15 days) of mesophilic digesters (20-30 days), meaning that the sludge daily flow rate could be doubled, or the reactor volume reduced, with subsequent savings in terms of sludge treatment costs. Furthermore, two-stage systems (70/55 ºC) may result in higher net energy production compared to single-stage systems (55 ºC) at 10 days SRT. However, the amount of surplus energy generated increases with digester volume. In spite of the decrease in methane production rate at increasing SRT, energy production is still higher than energy consumption, and therefore the bigger the amount of sludge in the digester, the higher the energy production.

Among the different available remediation technologies, it is well-known that bioremediation methods which mainly depend on microorganisms to degrade, transform, detoxify or break down the contaminants, they are recognized as cost-effective and environmental-friendly methods. In fact, microorganisms “engine of bioremediation process” carry out their normal duty under aerobic or anaerobic conditions, which without doubt extends and motivates the desires to make use of such abilities to reduce environmental threats caused by various contaminants. However, to achieve satisfactory results during any bioremediation process, providing optimal conditions for microorganisms is considered as an essential/crucial task. Composting as one of the applied bioremediation technologies used to remediate soils contaminated with organic contaminants like PAHs still needs more investigation although a valuable effort has been devoted to elucidate the behaviour of this process in the remediation of PAHs-contaminated soils. However, till recently, anaerobically treatment of PAHs-contaminated soil received less attention as it was believed that PAHs are poorly or even impossible to be degraded under such conditions. Therefore, the present study tried to touch both aerobically bioremediation of PAH-contaminated soil through composting and anaerobically treatment of the same soil under strict methanogenic conditions. For both remediation approaches, the effect of some controlling factors had been also evaluated through experiment design methodology employing central design (CCD) technique. Regarding the composting process, the obtained results demonstrated that this technology is an advantageous and indisputable method to decontaminate PAHs-contaminated soils within short period. Additionally, compost derived from the organic fraction of municipal solid wastes (OFMSW) was found to enhance the contaminants (PAHs) removal rate to high extent. Moreover, a lucid correlation between the contaminants removal rate and the compost stability degree was observed, such that more stable composts better enhanced the remediation process as these composts are believed to have a considerable fraction of humic matter which facilitates the desorption of the contaminants, and get more available as a consequence. At the same time, treatments with stable composts do not produce high temperature during the composting process, and normally they are in the mesophilic ranges which are more favourable for such bioremediation process. Bioaugmentation of the process through introducing white-rot fungi with desired catalytic capacity (Trametes Versicolor) in attempt to accelerate the degradation process demonstrated that no effect or enhancement was achieved through such approach. In the second part of the research, anaerobically treatment of PAHs-contaminated soil has been investigated under strict methanogenic conditions employing two types of inocula; thermophilic and mesophilic. The obtained results demonstrated the effectiveness of such biological treatments in this field. Nevertheless, the process was relatively less effective compared with composting. Furthermore, under these conditions and due to unclear reasons, reversible results were obtained as PAHs concentrations were increased with prolonged incubation, indicating the reversed bioformation of PAHs under such oxygen-deficient conditions. Therefore, future work should be devoted to clarify the reasons behind this behaviour.

Waste activated sludge (WAS) is one of the largest by-products of biological wastewater treatment. Anaerobic digestion of WAS is beneficial for several reasons. In an ever increasingly energy conscientious world the production of renewable energy resources is becoming more important, and thus the production of methane has been seen as a valuable product. To achieve efficient conversion of organic matter to methane, the biomass in the digester must be provided optimal operating conditions, as well as adequate retention times, that will allow for substrate metabolism and prevent bacteria washout. Two approaches have been taken in this research to achieve improved biodegradation. Initially microwave pretreatment was employed to improve the biodegradability of the sludge, then the addition of a submerged hollow fibre membrane separation unit was used to allow for a longer SRT while maintaining the hydraulic residence time (HRT). The impact of microwave pretreatment on WAS characteristics was assessed for both the low temperature operations and the high temperature operations. An increase due to pretreatment on the filtered to total COD ratio when comparing the feed to the microwaved feed was established to be 200 % for low temperature operations and 254 % for high temperature operations. For the low temperature operations, CODT destruction, VS destruction, and organic nitrogen destruction were all higher for the test digester than the control digester indicating that the microwaving of the WAS increased the biodegradation in the anaerobic digester. For the high temperature operation, CODT destruction and organic nitrogen destruction were improved with microwave application, however VS destruction did not support this. The measured biogas data indicated that microwaving did influence the volume of biogas produced during anaerobic digestion of WAS for both the low and high temperature operations, and hence the VS destruction data for the high temperature operations was determined to be incorrect. For the membrane operations both the CODT and the VS destruction calculations indicated that at the same SRT the test digester was capable of more biodegradation than the control digester. The control digester organic nitrogen reduction was calculated to be higher than for the test digester, suggesting that the control digester removed more organic nitrogen than the test digester, however, these results were likely due to the lower HRT of the test digester compared to those of the control digester. A greater volume of biogas was produced by the test digester than the control digester; however, the composition of the gas from both digesters was similar, although the percentage of methane produced by the test digester was higher than that produced by the control digester. The higher destruction by the test digester indicated that the presence of the membrane unit and the decoupling of the HRT and SRT improved the biodegradation capability of the digesters. The results of the membrane performance study indicated that for a hollow fibre anaerobic membrane bioreactor, stable operations could be achieved with a total solids concentration of 2.01 %+/-0.34, an HRT of 15 days and an SRT of 30 days. With a constant flux of 14 L/m2-h +/-0.68 the average TMP was 0.079 kPa/min+/-0.08. No cleaning was required to achieve this, however the operations consisted of 20 minutes of permeation followed by 5 hours and 40 minutes of relaxation. The critical flux was determined to be in the range of 18 to 22 L/m2-h.

Waste activated sludge (WAS) is one of the largest by-products of biological wastewater treatment. Anaerobic digestion of WAS is beneficial for several reasons. In an ever increasingly energy conscientious world the production of renewable energy resources is becoming more important, and thus the production of methane has been seen as a valuable product. To achieve efficient conversion of organic matter to methane, the biomass in the digester must be provided optimal operating conditions, as well as adequate retention times, that will allow for substrate metabolism and prevent bacteria washout. Two approaches have been taken in this research to achieve improved biodegradation. Initially microwave pretreatment was employed to improve the biodegradability of the sludge, then the addition of a submerged hollow fibre membrane separation unit was used to allow for a longer SRT while maintaining the hydraulic residence time (HRT). The impact of microwave pretreatment on WAS characteristics was assessed for both the low temperature operations and the high temperature operations. An increase due to pretreatment on the filtered to total COD ratio when comparing the feed to the microwaved feed was established to be 200 % for low temperature operations and 254 % for high temperature operations. For the low temperature operations, CODT destruction, VS destruction, and organic nitrogen destruction were all higher for the test digester than the control digester indicating that the microwaving of the WAS increased the biodegradation in the anaerobic digester. For the high temperature operation, CODT destruction and organic nitrogen destruction were improved with microwave application, however VS destruction did not support this. The measured biogas data indicated that microwaving did influence the volume of biogas produced during anaerobic digestion of WAS for both the low and high temperature operations, and hence the VS destruction data for the high temperature operations was determined to be incorrect. For the membrane operations both the CODT and the VS destruction calculations indicated that at the same SRT the test digester was capable of more biodegradation than the control digester. The control digester organic nitrogen reduction was calculated to be higher than for the test digester, suggesting that the control digester removed more organic nitrogen than the test digester, however, these results were likely due to the lower HRT of the test digester compared to those of the control digester. A greater volume of biogas was produced by the test digester than the control digester; however, the composition of the gas from both digesters was similar, although the percentage of methane produced by the test digester was higher than that produced by the control digester. The higher destruction by the test digester indicated that the presence of the membrane unit and the decoupling of the HRT and SRT improved the biodegradation capability of the digesters. The results of the membrane performance study indicated that for a hollow fibre anaerobic membrane bioreactor, stable operations could be achieved with a total solids concentration of 2.01 %+/-0.34, an HRT of 15 days and an SRT of 30 days. With a constant flux of 14 L/m2-h +/-0.68 the average TMP was 0.079 kPa/min+/-0.08. No cleaning was required to achieve this, however the operations consisted of 20 minutes of permeation followed by 5 hours and 40 minutes of relaxation. The critical flux was determined to be in the range of 18 to 22 L/m2-h.

The human colon is an anaerobic environment densely populated with bacterial species, creating what is known as the human intestinal microbiome; an ecosystem imperative to physiological function with regards to metabolism of non-digestible residues, growth of cells and immune protection from invading organisms. As such, quantifying, and subsequently developing an understanding of the behaviour of this microbial population can be of great value. Unfortunately, because of the physical inaccessibility of many parts of the gastro-intestinal (GI) tract, routine experimentation with this environment is not practical. However, theoretical modelling techniques including in vitro and in silico simulation/experimental platforms provide a means by which further studying of intestinal microflora can be approached. Perfecting these theoretical models is an important step in further understanding colon microbiota. An existing in silico model of carbohydrate digestion in the colon, developed by Munoz-Tamayo et al. (2010) has been used as a platform for experimentation with the intention of of discovering features which may be removed and/or added to improve the performance and reliability of the design. The model is an adaptation of the waste-water engineering based mathematical model ADM1 (Anaerobic Digestion Model 1), developed to incorporate biochemical and environmental specifications as well as physical structures particular to the human colon. The model is then a system of 102-ordinary differential equation with 66 parameters.Simulations with the default model configuration as well as variations of input variables, namely dietary fiber consumption and system flow rate, were completed to study the effect on average biomass concentration, demonstrating significant sensitivity to input variables and an unexpected linearity based on the non-linearity of the original complex system. Simulations and further study suggest that advancements in in silico modelling of the colon rely on the development of a metric or scheme that can effectively compare mathematically generated data with that collected through traditional experimentation. Also, experimenting with various reactor configurations as a basis for mathematical modelling may prove simpler configurations capable of generating comparable data to more complicated designs which may then also be applicable to existing in vitro representations of the colon.

The subjection of soils to degradation directly and indirectly from rising world food demand and resultant intensified agricultural production, population growth, and climate change, demand that soils are better protected. The role of AD in addressing this challenge is examined using a pragmatic research paradigm and the questions: How can we raise awareness of AD in the UK? What factors motivate and hinder farmers towards adopting improved technology and sustainable agricultural practises? What is the perception of farmers about soils? To what extent does sustainable agriculture incorporate soil conservation in theory and practice? What role can legislation and policies play in AD adoption in the UK? The research was in two phases; qualitative and quantitative. The qualitative phase involved interviews with 21 AD stakeholder in the UK using electronic mail. The stakeholders who were divided into groups according to their expertise, were interviewed to explore their views on the areas of focus in the UK strategy and action plan regarding raising awareness of the technology, soil conservation, sustainable agriculture and sustainable development. Thematic analysis of interview data was carried out using MAXQDA 11 statistical software. The quantitative phase involved an online survey of 283 UK farmers aided by Yellow Pages directory for UK, Natural England directory, Twitter and electronic mail. Using SPSS 22.0 statistical software, the Chi square test was used to check for relationships between the variables measured at 95% confidence level (p < .05). Relationship strength was measured by means of Cramer’s V and Phi values. Answers to the 1st research question showed that: aligning AD with sustainable development goals, community AD and localism, small AD plants, provision of an available market for AD products, building UK skills and diversifying biogas use from AD are positive options for raising awareness of AD. Response to 2nd research question revealed: significant relationships between interests in agricultural technology and gender, level of education, and farm size; between knowledge of what AD is and gender, level of education and farm size; between interest in AD and age; between willingness to invest in AD if it improved soil properties and farm ownership; and between organic farming practice and age, farm type and farm size. Responding to the third research question, farmers’ describe soils in abstract, scientific, physical attribute and functional terms; awareness of soil benefits other than crop production was significantly related to age, and farm ownership; educational level was significantly related to familiarity with soil conservation, and opinion on whether soil should be protected like other natural resources. Findings regarding the 4th and 5th research questions showed: limited understanding of soil matters as a key challenge that has restricted the priority given to soil conservation, while level of education, knowledge of soil conservation and sustainable development and understanding of sustainable agriculture were also identified as influencing factors; digestate from AD is the main benefit viewed to contribute to soil conservation; finance, policy and legislation, low awareness and understanding, lack of feedstock and market, land use conflict and inefficiency of AD plants were identified as barriers to AD in the UK; promoting AD, providing finance, minimizing bureaucracy and simplification of AD systems are options for promoting AD adoption. This thesis also documents the implications of these findings for knowledge, policy and practice, and based on these recommendations are made, some of which are: better engagement of farmers in policy development for AD and soil management; use of small AD plants, demonstration, networking and training for AD adoption; promote soil conservation in theory and practice; and provision of enhanced support for owners, potential investors and farmers through incentives, simplified planning approval process, and available market for AD product.

A vinhaça, água residuária do processo, apresenta em sua composição DQO de 20 a 100 g DQO.L-1 e um ótimo potencial de produção de biogás por meio da digestão anaeróbia. Para avaliar a capacidade de produção de biogás, foram realizados experimentos sob o efeito gradual da carga orgânica volumétrica (COV) e da relação A/M, avaliando a etapa metanogênica. Como no processo de fabricação do etanol é adicionado ácido sulfúrico para evitar a contaminação bacteriana, foi avaliado a interferência da adição de diferentes concentrações de sulfetos no processo em valore de pH 7,0 e 7,5. O fermentador foi alimentado com Na2S.9H2O, variando a concentração do íon S2- de 0 a 1000 mg.L-1. Para obter uma boa eficiência na produção de metano, a etapa acidogênica também foi avaliada. Para isso, se manteve as mesmas concentrações de biomassa e substrato, porém, ajustando os valores de pH em 5,0, 5,5, 6,0 e 6,5. Na etapa metanogênica uma satisfatória redução da elevada carga orgânica presente na vinhaça foi alcançada, com eficiência de remoção entre 82,0% e 90,3% em processo mesofílico. Um ajuste polinomial foi realizado para avaliar a produção específica de metano, que variou de 379 mL CH4.h-1 a 872 mL CH4.h-1 e atividade metanogênica de 0,33 mmol CH4.gSVT-1 h-1 a 0,77 mmol CH4.gSVT-1 h-1. Para a etapa da sulfetogênese, o pH afetou consideravelmente o desempenho das arqueas metanogênicas, ocorrendo inibição mais acentuada para o pH 7,5. Na concentração mais baixa testada, de 50 mg S2-.L-1, foi observada inibição de 31,85% para pH 7,0 e de 67% para pH 7,5 e para a concentração mais elevada de 1000 mg S2-.L-1 a inibição foi de 59,75% e de 94,07% respectivamente. Na última etapa da acidogênese, maiores concentrações de ácido propiônico e acético foram alcançadas em pH 5,0 e 5,5, com 1374,66 e 1477,23 mg C3H6O2.L-1 e 993,05 e 767,80 mg CH3COOH.L-1. Maiores taxas de produção de AGV ocorreram em pH 6,5, alcançando para o ácido propiônico 8,82 mmol.d-1 gSVT-1 e 7,99 mmol.d-1 gSVT-1 para ácido acético. A produção acumulada de metano nas primeiras 60 horas atingiu 2210 mL, 5300 mL, 7210 mL e 7620 mL CH4, respectivamente para pH 5,0, 5,5, 6,0 e / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2017-07-12T18:44:50Z No. of bitstreams: 1 Dissertacao Vanessa Verona Peruzzo.pdf: 3017795 bytes, checksum: 5aad4de95a823b85afe45b94c6cd1fc0 (MD5) / Made available in DSpace on 2017-07-12T18:44:50Z (GMT). No. of bitstreams: 1 Dissertacao Vanessa Verona Peruzzo.pdf: 3017795 bytes, checksum: 5aad4de95a823b85afe45b94c6cd1fc0 (MD5) Previous issue date: 2017-07-12 / Centro de Pesquisa e Desenvolvimento Leopoldo Américo Miguêz de Mello, CENPES. / The vinasse, wastewater of the process, presents in its composition a COD of 20 to 100 g COD.L-1 and an excellent biogas production potential through anaerobic digestion. To evaluate the biogas production capacity, experiments were carried out under the gradual effect of organic volumetric load (OVL) and A/M ratio, evaluating the methanogenic step. Considering that sulfuric acid is added to the ethanol production process to prevent bacterial contamination, the interference of the addition of different sulfide concentrations in the process at pH 7.0 and 7.5 was evaluated. The fermenter was fed with Na2S.9H2O, varying the concentration of the S2- ion from 0 to 1000 mg.L-1. In order to obtain good efficiency in the production of methane, the acidogenic step was also evaluated. For this, the same concentrations of biomass and substrate were maintained, however, the pH to was adjusted 5.0, 5.5, 6.0 and 6.5. In the methanogenic stage a satisfactory reduction of the organic load present in the vinasse was achieved, with removal efficiency in the range of 82.0% and 90.3% for mesophilic process. A polynomial fit was performed to evaluate the specific production of methane, ranging from 379 mL CH4.h-1 to 872 mL CH4.h-1 and a methanogenic activity of 0.33 mmol CH4.gSVT-1 h-1 at 0.77 mmol CH4.g SVT-1 h-1. For the sulfetogenic stage, the pH considerably affected the performance of the methanogenic archaea, with a more pronounced inhibition at pH 7.5. The lowest concentration tested, 50 mg S2-.L-1, resulted in an inhibition of 31.85% inhibition pH 7.0 and 67% at pH 7.5. The highest concentration, 1000 mg S2-.L-1, the inhibition was 59.75% and 94.07% respectively. Higher concentrations of propionic and acetic acid were reached at pH 5.0 and 5.5, with 1374.66 and 1477.23 mg C3H6O2.L-1 and 993.05 and 767.80 mg CH3COOH.L-1. Higher rates of VFA production occurred at pH 6.5, yielding 8.82 mmol.d-1 gSVT-1 and 7.99 mmol.d-1 gSVT-1 for acetic acid for propionic acid. Cumulative methane production in the first 60 hours increased 2210 mL, 5300 mL, 7210 mL and 7620 mL CH4, respectively to pH 5.0, 5.5, 6.0 and 6.5.