Continuous flow, daily fill and draw, and batch aeration digesters were studied on a laboratory scale, to develop low temperature characteristics and design criteria for aerobic digestion of waste activated sludge. These results were compared against full-scale data from three independent sources. Raw sludge used in these studies was obtained from a municipal high rate activated sludge plant. The digestion systems were operated at liquid temperatures of 20, 10, and 5°C, and at six different sludge ages. Measurement of all parameters studied for the continuous feed systems were made under steady-state conditions. Parameters studied were divided into three main groups, namely: (1) Parameters related to aerobic digestion kinetics, such as solids destruction and oxygen uptake rate; (2) Parameters related to aerobic digestion sludge characteristics, such as biochemical oxygen demand, viable bacteria, organic carbon, nitrogen forms, and odour values; (3) Parameters relating to supernatant quality, such as dissolved solids, organic carbon, biochemical oxygen demand, chemical oxygen demand, nitrogen forms, and pH. The results show that the effect of low temperature on aerobic digestion performance was pronounced. The combined effect of sludge age and temperature was shown to be an important design parameter. Kinetic reaction rates and temperature sensitivity coefficients were calculated for the various conditions studied on the basis of volatile suspended solids. It was shown that reaction rates for batch digestion and continuous feed digestion systems were not interchangeable. This is significant, as most pilot plant and bench-scale studies on aerobic digestion are being conducted using batch digestion, the results of which are then being used for design of continuous feed digesters. It appears that, as temperature decreases, the daily fill and draw method of digester operation resulted in significantly higher reaction rates than the continuous feed method of digester operation. At higher temperatures, the two were about equal. Oxygen uptake rate was not considered a reliable indicator of digested sludge stability; instead, mixed liquor BOD₅, was introduced as a possible means of determining such stability. Nitrification and denitrification is shown to be appreciable during aerobic digestion in all systems and at all temperatures studied. Although somewhat tentative, the results show important nitrification and denitrification trends at temperature and pH levels well below optimum values for these processes. The difference between batch and continuous feed digestion is shown in various ways, but probably most clearly through monitoring supernatant characteristics. The continuous feed systems show increased solubilization of organics with increased sludge age, whereas the batch systems do not show any solubilization of organics. Reasonable correlation is demonstrated between the laboratory and full-scale aerobic digestion data. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Pressure changes and myoelectrical activity in the ovine rumen were investigated following the surgical implantation of fluid filled balloon-tipped tygon tubes and paired fine needle platinum electrodes. The correlations among rumen pressure change and myoelectrical spike burst duration, frequency and magnitude data from 447 7 one minute periods were determined in order to select a single reliable quantitative measurement of rumen motility. The results showed that all these parameters accurately reflect activity changes in the rumen. Myoelectrical spike burst duration was shown to be the most sensitive indicator and was used as the criterion for examination of lactic acid induced motility changes. Rumen motility was not affected by intraruminal introduction of 1000 ml of 0.15 or 0.7 M lactic acid at pH 2.0 via permanently implanted cannulae. Intravenous infusion of 2 concentrations of sodium lactate which increased blood lactate levels by approximately 20 mg% and 180 mg% respectively, also had no effect on rumen motility. Infusion of lactic acid solutions (250 ml) 0.15 or 0.7 M (pH 2.0, 4.0 and 6.0) intraduodenally via polyethylene cannulae exerted profound effects on rumen motility. Immediately following ( 1 min) the commencement of the infusion of lactic acid (pH 2.0), a short period of total inhibition of motility occurred which was followed by a rapid recovery of motility to near normal levels despite the continuation of the infusion. These initial short periods of inhibition and recovery continued for up to one hour following termination of infusion. Similar yet somewhat reduced responses were observed upon intraduodenal infusion of the lactic acid solutions at pH 4.0 and 6.0. These results suggest that inhibition of rumen motility in lactic acidosis may be caused primarily by lactic acid produced in the rumen entering the intestine and causing a stimulation of the enterogastric reflexes. / Land and Food Systems, Faculty of / Graduate

No description available.

Please read the abstract in the section 00front of this document / Thesis (PhD (Food Science))--University of Pretoria, 2006. / Food Science / unrestricted

Sustainable and environmentally friendly waste-to-energy conversion technologies, such as anaerobic digestion (AD) and gasification, have received significant attention in recent energy research. These technologies have proven their ability to reduce reliance on fossil fuels and greenhouse gas emissions by converting organic waste into products and fuels with market value, such as biomass, biogas, and synthetic gas. Since the syngas produced by biomass gasification contains highly toxic CO and flammable H₂, converting syngas into renewable natural gas has recently gained a lot of interest. By coupling AD with syngas, microbial consortium in the AD reactor converts the syngas into methane through a process known as biomethanation. Feeding syngas into the AD reactor is a method that not only can enhance methane production by conversion of CO₂ to CH₄ during the AD process but also converts syngas into methane as pure energy. This study aims to assess and compare the effect of different syngas compositions on methane production and optimize the SB process by identifying the best syngas composition and gas-biomass ratio under mesophilic temperature conditions. The study was conducted using batch and semi-continuous reactors in a lab-scale setting. The results of this study can contribute to the development of more efficient and sustainable methods for SB. In phase I of this study, syngas biomethanation under different syngas compositions was conducted under three different gas-biomass ratios (0.5, 1 and 1.5) in bench-scale experiments to study the impact on CO and H₂ partial pressure and CO toxicity on operation parameters (e.g., pH and VFA) and syngas conversion efficiency. The results showed that the optimum syngas composition with the highest amount of CH₄ is H₂-rich syngas (CO₂:CO; H₂ 1:1:7) and syngas with stoichiometric ratios between H₂ and CO/CO₂ (CO:H₂ 1:3; CO₂:H₂ 1:4) because of the sufficient available amount of hydrogen in the headspace. Methane content in the produced biogas reached 80.0%, 63.6% and 57.7%, respectively, compared to the control sample with 30.2% methane in the headspace. In phase II, the optimum syngas compositions were selected for experimenting with semi-continuous mode to 1) investigate the effect of injecting syngas in several stages in increasing syngas conversion efficiency, 2) adapt microorganisms to hydrogen and enhance biohydrogen production, and 3) test higher stoichiometric ratio between H₂ and CO/CO₂ to enhance syngas biomethanation efficiency. The data indicated higher methane content and syngas conversion in a semi-continuous mode. The biogas had methane concentration of 82.3, 76.9, 73.8, 84.9 and 81.7% in samples CO₂:CO: H₂ (1:1:7), CO:H₂ (1:3), CO₂:H₂ (1:4), CO: H₂ (1:4) and CO₂:H₂ (1:5). By injecting gas into the biomass in several stages, methane levels in the produced biogas in each stage increased, demonstrating the adaptation of microorganisms to the injected hydrogen and carbon-sourced gases. A higher stoichiometric ratio of H₂ to CO/CO₂ promoted the growth and activity of methanogens, leading to increased methane production.

No description available.

No description available.

No description available.

Optimiser l'utilisation des nutriments par le porc, particulièrement l'azote et le phosphore qui sont essentiels à la croissance des porcs, mais peuvent être dommageables pour l'environnement, est un élément clé pour la durabilité de la production. Pour une évaluation plus précise des ingrédients, une bonne compréhension de la disponibilité de la ration et des nutriments à l'intérieur du tractus digestif est de mise. Le tractus gastrointestinal (TGI) est un milieu présentant un mélange complexe de macromolécules, microorganismes et enzymes qui interagissent ensemble pour extraire et fournir les nutriments à l'animal. Les caractéristiques physico-chimiques, telles que le pH et le temps de transit du digesta, peuvent altérer le processus digestif en incluant l'efficacité des enzymes, l'absorption de nutriments et la fermentation microbienne. Les essais nutritionnels conduits pour évaluer la valeur nutritive des rations incluant leur digestibilité sont souvent réalisés avec des porcs restreints nourris avec un ou deux repas par jour. Cependant, ces conditions ne sont pas celles généralement retrouvées en élevage. En plus de la taille et de la fréquence des repas, le temps de transit et donc la capacité digestive des porcs peuvent être affectés par la composition de leur ration. Parmi les composantes de la ration, les fibres alimentaires sont reconnues pour modifier le temps de transit et la capacité digestive. Ainsi, de nos jours, le type de ration et son impact sur la digestibilité est à revoir car les aliments peuvent inclure une grande proportion d'ingrédients alternatifs riches en fibres pour remplacer une partie du maïs et du tourteau de soya. Des enzymes exogènes sont fréquemment ajoutées aux aliments pour porcs afin d'améliorer la digestibilité du phosphore phytique (phytase) et de la fibre (xylanase). En plus de leur action spécifique sur le phosphore et les fibres, ces enzymes peuvent agir de manière positive sur la valeur nutritionnelle globale en améliorant la digestibilité des minéraux, des acides aminés et de l'énergie. La première étude de cette thèse visait à évaluer l'impact de la granulation et du type de ration sur la digestibilité des nutriments. Cette étude a montré que la granulation permet d'augmenter la digestibilité des nutriments et de réduire la variation de digestibilité dépendamment de la source d'ingrédients utilisés. Par ailleurs, l'inclusion de 30 % de coproduits dans la ration n'a pas diminué la digestibilité des nutriments ou de l'énergie. La deuxième étude avait pour but de déterminer l'impact de la fréquence et la taille de repas et l'ajout d'enzymes exogènes sur la digestibilité des nutriments d'une ration riche en fibres. Les résultats ont montré que la fréquence et la taille des repas ont un faible impact sur la digestibilité affectant seulement l'amidon et le calcium. En revanche, la supplémentation en enzymes a permis d'améliorer la digestibilité de la matière sèche et des fibres ainsi que du phosphore et du calcium. La dernière étude visait à évaluer l'impact de la fréquence et la taille de repas et du type de ration (faible ou riche en fibres) sur la digestibilité des nutriments et le transit gastrointestinal. Cette étude a montré que le transit peut être modifié par un changement de la fréquence et taille de repas et était ainsi augmenté par des repas moins fréquents (deux fois par jour). Par ailleurs, le transit était plus long lorsque la ration servie était riche en fibres. Les porcs nourris avec plusieurs repas par jour (huit repas par jour) obtenaient une meilleure digestibilité de la matière sèche et des fibres indépendamment du type de ration. En conclusion, les résultats de cette thèse montrent que la fréquence et la taille de repas peuvent modifier le temps de transit selon le type de ration servie aux porcs. Par contre, la digestibilité des nutriments était faiblement modifiée par les caractéristiques du repas. D'autre part, la supplémentation en enzymes exogènes et la granulation sont deux moyens d'augmenter la digestibilité des rations. / Optimizing the use of nutrients by pigs, especially nitrogen and phosphorus which can be harmful to the environment and essential for pig growth, is a key element for the sustainability of production. For a more accurate evaluation of the ingredients, a good understanding of the fate of the diet and the nutrients within the digestive tract is required. The gastrointestinal tract (GIT) is a medium with a complex mixture of macromolecules, microorganisms and enzymes that interact together to supply nutrients to the animal. Physicochemical characteristics, such as pH and transit time, can alter the digestive process including the efficiency of enzymes, nutrient uptake and microbial fermentation. Digestibility trials conducted to assess the nutritional value of rations as well as their digestibility are often carried out with restricted pigs fed one or two meals a day. However, these conditions are not those found in commercial farms. In addition to the size and frequency of meals, the transit time and therefore the digestive capacity of pigs can be affected by the composition of their diet. Among the components of the feed, dietary fibers are known to modify transit time and digestive capacity. Thus, the type of diet is of particular concern nowadays since diets can include a large proportion of alternative high-fibre ingredients to replace some of the corn and soybean meal. Exogenous enzymes are frequently added to pig diet to improve the digestibility of phytic phosphorus (phytase) and fibre (xylanase). In addition to their specific action on phosphorus and fibre, these enzymes can have a positive effect on the overall nutritional value by improving the digestibility of minerals, amino acids and energy. The first study of this thesis aimed to assess the impact of pelleting and type of diet on nutrient digestibility. This study has shown that pelleting increases the digestibility of nutrients and reduces variation in digestibility depending on the source of ingredients used. Also, the inclusion of 30% byproducts in the diet did not decrease nutrient or energy digestibility. The second study aimed to determine the impact of frequency and size of meals and the addition of exogenous enzymes on the digestibility of nutrients in a high fibre diet. The results showed that the frequency and size of meals had a low impact on digestibility affecting only starch and calcium. In contrast, supplementation with enzymes improved the digestibility of dry matter and fibre as well as phosphorus and calcium. The last study aimed to assess the impact ivof frequency and size of meals and type of diet (low or high in fibre) on nutrient digestibility and gastrointestinal transit. This study showed that the transit can be altered by a change in the frequency and size of meals and was thus increased by less frequent meals (twice a day). In addition, transit was longer when the diet served was rich in fibre. Pigs fed several meals per day (eight meals per day) obtained better digestibility of dry matter and fibre regardless of the type of diet. In conclusion, the results of this thesis show that the frequency and size of meals can modify the transit time depending on the type of diet fed to the pigs. The digestibility of nutrients was however marginally modified. On the other hand, supplementation with exogenous enzymes and granulation are two ways of increasing the digestibility of nutrients.

La phase de démarrage est une étape critique pour les opérateurs de digesteurs anaérobies en raison des instabilités rencontrées, qui peuvent entraîner une réduction du flux de déchets à traiter, voire un arrêt complet du digesteur, nécessitant un redémarrage. Ces problèmes entraînent des pertes économiques importantes dues à l'accumulation de déchets organiques et à des coûts d'exploitation non optimaux de l'usine de biogaz (chauffage, moteurs, etc.). Ce projet de thèse vise à développer des approches pour comprendre les dynamiques de la phase de démarrage afin de permettre une application efficace, l'élaboration de protocoles standardisés et une prise de décision éclairée. Pour ce faire, la thèse a été divisée en deux phases : 1) la Phase 1 est conçue pour définir les principes fondamentaux menant à des phases de démarrage réussies, et 2) la Phase 2 vise à établir des lignes directrices pour la prise de décision afin d'optimiser la sélection et la mise en œuvre de l'inoculum dans les digesteurs anaérobies. Dans la phase 1, les principes de base de la digestion anaérobie sont définis au chapitre 1, suivis des particularités de la phase de démarrage au chapitre 2. Ainsi, les défis uniques liés à la phase de démarrage ont été soulignés et l'importance de l'inoculum au cours de la planification du démarrage a été mise en évidence. La plupart des données expérimentales examinées sont ensuite normalisées et compilées dans une base de données au chapitre 3. Cela a permis d'appliquer des méthodes statistiques et d'apprentissage automatique pour saisir les corrélations cachées entre les paramètres étudiés et la durée du démarrage. La base de données développée comprenait 90 % de cas de démarrage réussis et 10 % de cas d'échec, résumant efficacement les conditions conduisant à des cas de démarrage réussis. L'étude de l'effet des paramètres d'exploitation sur la durée de la phase de démarrage a mis en évidence l'importance du contrôle du régime d'alimentation pendant la phase de démarrage en maintenant un temps de rétention hydraulique (TRH) suffisamment bas, même si le contenu organique de substrat est élevé, grâce à une gestion optimale du taux de charge organique (TCO) sans dilution de substrat. Cependant, la base de données développée n'a pas pu capturer l'impact de l'inoculum sur la durée de démarrage en raison du manque de détails rapportés dans la littérature. Par conséquent, la deuxième phase se concentre sur le développement de lignes directrices pour une meilleure sélection et mise en œuvre de l'inoculum dans les digesteurs anaérobies. Dans un premier temps, les indicateurs pertinents de la performance de l'inoculum liés à la température et aux caractéristiques sont identifiés au chapitre 4 par le biais d'expériences en batch. Les concentrations initiales d'ammoniac total, d'alcalinité, d'acides gras volatiles (AGV) et la température de l'inoculum sont les principales caractéristiques reflétant la diversité bactérienne et la cinétique de l'inoculum. Le chapitre 5 étudie l'impact de la stabilisation de l'inoculum et de la réponse à des événements d'alimentation extrêmes sur la phase de démarrage au cours d'une expérience semi-continue de 115 jours. Lors d'événements d'alimentation extrêmes, le digestat thermophile stabilisé a montré une plus grande sensibilité aux charges organiques élevées, alors que le réacteur ensemencé avec du digestat thermophile frais a été plus influencé par la suspension de l'alimentation. Une fois que les deux digesteurs ont atteint le régime permanent, des différences mineures ont été observées entre les deux réacteurs. Enfin, le chapitre 6 met en évidence l'effet du choix de l'inoculum sur les performances économiques des systèmes de digestion anaérobie. Il a été constaté que la matière digérée (digestat) utilisée comme inoculum conduit à une meilleure performance des réacteurs pendant la phase de démarrage que la matière non digérée (boues municipales). En effet, le coût de production d'un mètre cube de méthane et de traitement d'un kilogramme de solides volatiles (SV) dans le digesteur inoculé avec du digestat était respectivement 18 et trois fois moins élevé que dans le digesteur inoculé avec des boues municipales diluées. Tout au long de ce projet de doctorat, les fondamentaux et les principes de la phase de démarrage sont présentés, suivis par le développement de lignes directrices pour la prise de décision concernant la sélection et la mise en œuvre de l'inoculum. / The start-up phase is a critical step for anaerobic digester operators due to the instabilities encountered, which can lead to a reduced flow of waste to be treated or even a complete shutdown of the digester, necessitating a restart. These issues result in significant economic losses due to the accumulation of organic waste and non-optimal operating costs of the biogas plant (heating, motors, etc.). This PhD project aims to develop knowledge-based approaches to understand the dynamics of the start-up phase for efficient application, the development of standardized protocols, and informed decision-making. To achieve this, the thesis has been divided into two phases: 1) the first phase is designed to define the fundamentals leading to successful start-up phases, then 2) the second phase targets the establishment of decision-making guidelines for optimizing the selection and implementation of the inoculum in anaerobic digesters. In Phase 1, the basic principles of anaerobic digestion are defined in Chapter 1, followed by the particularities of the start-up phase in Chapter 2. As such, the unique challenges related to the start-up phase have been outlined and the importance of the inoculum during the start-up planning has been highlighted. Most of the reviewed experimental data are then standardized and compiled into a database in Chapter 3. This allowed for applying statistical and machine learning methods to capture hidden correlations between the studied parameters and start-up duration. The developed database included 90 % successful and 10 % failed start-up cases, effectively summarizing conditions leading to successful start-up cases. The study of the impact of operating parameters on the start-up phase duration highlighted the importance of controlling the feeding regime during the start-up phase by maintaining sufficiently low hydraulic retention time (HRT), even if the organic content of the feed is high, through optimal organic loading rate (OLR) handling without feed dilution. However, the developed database couldn't capture the impact of the inoculum on the start-up duration due to insufficient reported details in the literature. Therefore, the second phase focuses on developing guidelines for the enhanced selection and implementation of the inoculum in anaerobic digesters. Initially, relevant indicators of inoculum performance related to temperature and characteristics are identified in Chapter 4 through batch experiments. Initial concentrations of total ammonia, alkalinity, VFA, and inoculum temperature were the main characteristics reflecting inoculum bacterial diversity and kinetics. Chapter 5 studies the impact of inoculum stabilization and response to extreme feeding events on the start-up phase during a 115-day semi-continuous experiment. Under extreme feeding events, the stabilized thermophilic digestate showed greater sensitivity to high organic loads, whereas the reactor seeded with fresh thermophilic digestate was more affected by feed suspension. Once both digesters reached the steady-state, minor differences were observed between the two reactors. Finally, Chapter 6 highlights the impact of inoculum choice on the economic performance of anaerobic digestion systems. It has been found that digested material (digestate) used as inoculum leads to a better performance of reactors during the start-up phase than undigested material (municipal sludge). Indeed, the cost of producing one cubic meter of methane and processing one kilogram of volatile solids (VS) in the digester inoculated with digestate was 18 and three times cheaper, respectively, than in the digester inoculated with diluted municipal sludge. Throughout this PhD project, the fundamentals and principles of the start-up phase are presented, followed by the development of decision-making guidelines for inoculum selection and implementation.