La structure et la texture des aliments solides et leur évolution pendant la digestion affectent leur désintégration et la vitesse de libération et de dégradation des protéines. Il a été démontré que la cinétique de digestion a un impact sur l’utilisation postprandiale des protéines. D'autre part, les différentes variétés de fromages présentent des caractères texturaux, variant de souple à ferme, selon les processus technologiques appliqués pour leur fabrication. Ce projet vise à étudier si, et comment, la structure et la texture des fromages affectent la désintégration et la digestion des protéines des fromages. Des fromages commerciaux de textures différentes ont été choisis pour la première étude. Leur désintégration et la digestion des protéines en modèle in vitro ont été caractérisées. Les résultats ont montré que la phase gastrique de la digestion représente l’étape clef de la désintégration. La désintégration à la fin de la digestion gastrique était corrélée négativement avec certains des paramètres texturaux du fromage initial (cohésion et élasticité). Cependant la désintégration était aussi corrélée positivement à la teneur en lipides du fromage. La libération et la dégradation des protéines variaient entre les fromages, en raison de leurs vitesses de désintégration différentes. La deuxième étude a examiné l’impact des changements de texture fromagère, induits par la réduction de la teneur en lipides du fromage seulement, sur la digestibilité des fromages de type Cheddar et Mozzarella. En réduisant la teneur en lipides du fromage Cheddar, la digestion des protéines était ralentie, en raison de sa désintégration plus lente. Par contre la réduction de la teneur en lipides n’influence pas la digestion des fromages Mozzarella, en raison de la faible réduction de la teneur en lipides du fromage qui joue un rôle limité sur la texture du fromage. La désintégration des fromages à la fin de digestion gastrique et duodénale était non seulement corrélée négativement à la cohésion et l’élasticité du fromage initial, mais aussi à la dureté du fromage initial. La troisième étude a vérifié l'impact du changement de la texture du fromage durant la digestion gastrique et son impact sur la désintégration du fromage, en utilisant les fromages de type Cheddar et Mozzarella, de composition et texture similaires, comme modèles. Dans les premières 15 min de la digestion gastrique, la contrainte de rupture (la pression nécessaire pour engendrer la rupture du fromage) était diminuée rapidement et la désintégration était rapide pour les fromages Cheddar et Mozzarella. De 15 à 120 min de la digestion gastrique, la contrainte de rupture était stable pour le fromage Cheddar, tandis qu’elle était diminuée graduellement pour le fromage Mozzarella. Cependant le fromage Cheddar était peu désintégré tandis que le fromage Mozzarella était désintégré graduellement. Ces résultats suggèrent que certaines variétés de fromages ont des cinétiques de digestion différentes qui influencent la digestion des protéines. / Recently, the food disintegration in stomach was reported to be affected by food structure and texture and their changes during digestion. This phenomenon should affect the kinetics of protein release and degradation in gastro-intestinal tract, which may affect protein postprandial utilization. Cheeses, depending on their processing parameters, have different structural and textural properties. This study aimed to understand how cheese structure and texture affect cheese disintegration and protein digestion during digestion. Firstly, cheese disintegration and cheese protein digestion were characterized for five commercial cheeses presenting different textural properties induced by different technological treatments. This study aimed to understand if cheese texture affects cheese digestibility. Results showed that gastric digestion was the critical step in cheese disintegration. Cheese disintegration at the end of gastric digestion was correlated negatively to cheese springiness and cohesiveness. Meanwhile cheese disintegration was also correlated positively to cheese initial fat content. The protein release and hydrolysis rates during gastric digestion were different among cheeses, related to their different disintegration rates. Secondly, the impact of cheese texture, induced by fat reduction only, on the digestibility of Cheddar and Mozzarella cheeses was studied. With decreasing fat content in Cheddar, the protein digestion slowed down explained by their slower disintegration. However, the reduction of fat in Mozzarella cheese had no impact on cheese disintegration and protein digestion, explained by the low fat reduction which presented limited effect on cheese texture. Cheese disintegration at the end of gastric and duodenal digestion was correlated negatively not only to cheese cohesiveness and springiness, but also to cheese initial hardness. Thirdly, the change of cheese texture during gastric digestion and its further effect on cheese disintegration were studied, using Cheddar and Mozzarella cheeses presenting similar compositional and textural properties as models. Results showed that during the first 15 min of gastric digestion, cheeses showed a sharp decrease of fracture stress (pressure at which the sample crumbles) meanwhile the disintegration was fast. From 15 to 120 min gastric digestion, the fracture stress of Cheddar remained stable while Mozzarella cheese showed a slow but gradual decrease of the fracture stress. During this time, Cheddar cheese was barely disintegrated, meanwhile the disintegration of Mozzarella was gradual. These results suggest that some cheese varieties show different digestion kinetics that modulate the digestion of cheese proteins.

The Blue Plains Wastewater Treatment Plant in Washington, D.C. is in the process of updating its anaerobic digesters, with a completion date set for 2008. This research was undertaken to aid designers at Blue Plains by evaluating alternative digestion approaches. The technologies applicable to the plant included thermophilic anaerobic digestion, acid/gas phased digestion, and temperature phased anaerobic digestion. To obtain design data, a year long study was conducted using bench scale digestion systems operating at different solids retention times (SRT) and organic loading rates (OLR). The digesters were fed with mixed primary and secondary waste (50/50 by weight) from the Blue Plains wastewater treatment facility. The digesters were operated until they reached steady state as observed by volatile solids reduction (VSR), methane production, and volatile fatty acid (VFA) levels. At this point, samples of digested waste sludge were analyzed for residual biological activity, dewatering properties and headspace organo-sulfur production. Results from the study demonstrated that the TPAD digestion process had the lowest residual biological activity (RBA) after digestion, and that the single stage thermophilic digesters had the highest RBA. Sludge from single stage mesophilic digestion had the highest odor potential, with headspace gas tests generating over 1400 mg organo-sulfur per m3 of headspace gas, while both single stage thermophilic and TPAD systems generated less than 400 mg/m3 at all SRTs studied. / Master of Science

The performance and stability of a thermophilic anaerobic digestion system are inherently dependent on the engineered environment within each reactor. While the selection of operational parameters such as mixing, solids retention time, and digestion temperature are often selected on the basis of certain desirable outcomes such as the deactivation of human pathogens, these parameters have been shown to have a broad impact on the overall sludge digestion process. Since the current time-temperature requirements for biosolids pathogen reduction are most easily met at elevated digestion temperatures within the thermophilic range, it is certainly worth examining the effect of specific digestion temperatures on ancillary factors such as operational stability and the aesthetic quality of biosolids. A series of experiments were carried out in which wastewater sludge was digested at a range of temperatures (35°C, 49°C, 51°C, 53°C, 55°C, 57.5°C). Each reactor was operated for a period at steady state in order to make observations of microbial activity, digestion performance, and biosolids aesthetics as affected solely by digestion temperature. Results of this study show that poor operational stability arises in reactors operated at 57.5°C. Elevated concentrations of hydrogen and short-chain fatty acids in the 57.5°C digesters are evidence that the observed temperature-induced digester failures are related to the temperature sensitivity of hydrogenotrophic (CO₂-reducing) methanogens. Reactors operated at other temperatures performed equally well with respect to solids removal and operational stability. In addition, peak volatile organic sulfur compound (VOSC) production from biosolids treated at 51°C and above was greatly reduced in comparison with mesophilic anaerobic digestion and a lower temperature (49°C) thermophilic system. Since the biosolids methanogenic community appeared to be equally capable of degrading VOSC over the range of thermophilic temperatures, the conclusion is that the activity of VOSC producing organisms in digested and dewatered biosolids is greatly reduced when operating temperature in excess of 51°C are used. This study shows that small changes in an operationally defined parameter such as digestion temperature can have a large impact on the performance and stability of a digestion process. Single minded selection of digestion temperature in order to achieve effective pathogen reduction can result in poor digester performance and the production of an aesthetically unacceptable product. Careful selection, however, of an appropriate digestion temperature can not only ensure successful pathogen reduction in compliance with current regulations, but can also improve the performance, stability, and aesthetic quality of digestion systems employing thermophilic anaerobic digestion. / Master of Science

Ce mémoire de maîtrise présente en détail le projet de recherche sur la valorisation des boues de procédé de l'entreprise Celanese, manufacturier de polymères situé à Boucherville. Les boues, contenant principalement du poly acétate de vinyle, sont présentement destinées à l'enfouissement, ce qui entraine des dépenses économiques importantes ainsi qu'un impact négatif sur l'environnement. Ce projet a comme objectif d'étudier la faisabilité de la digestion anaérobie comme solution de valorisation et de proposer la meilleure option de valorisation à Celanese. En premier lieu, une mise en contexte présente la compagnie Celanese et les objectifs du projet. Puis, le premier chapitre présente en détail la digestion anaérobie, son utilité et la théorie associée au test de potentiel biométhanogène. Ensuite, la méthodologie présente les étapes effectuées par l'étudiant pour répondre aux objectifs du projet. La méthodologie inclut les étapes de l'échantillonnage, la caractérisation, le test de potentiel biométhanogène et les prétraitements aux boues pour améliorer les résultats. La section résultats présente par la suite les résultats de la caractérisation et des deux essais du test de potentiel biométhanogène. Finalement, une analyse technico-économique est présentée à la fin pour évaluer la rentabilité du projet. Les recommandations finales indiquent que la digestion anaérobie des boues non traitées n'est pas réalisable en raison du manque de production de gaz. De son côté, la digestion anaérobie des boues traitées améliore la production, mais l'analyse économique préliminaire indique que le projet ne serait pas rentable selon les critères de Celanese. Le dernier chapitre présente une alternative à la digestion anaérobie, soit la pyrolse. Les résultats d'une analyse thermogravimétrique semblent montrer que la pyrolyse est prometteuse. La recommandation générale du projet est d'évaluer dans le futur la pyrolyse des boues de Celanese plutôt que la digestion anaérobie. / This Master thesis presents the details of the research project concerning the valorization of process sludge of Celanese, polymers manufacturer located in Boucherville. Their sludge, containing mainly polyvinyl acetate, is currently destined to landfilling, which causes economic and environmental problems to the company. The objective of this project is to study the feasibility of anaerobic digestion as a solution of the valorization and to recommend the best solution to Celanese. First, the general context of the project is presented, with presentation of the company Celanese and the project objectives. Then, the first chapter presents in detail the anaerobic digestion, its utility and the theory related to the biomethane potential test. Then, the methodology chapter presents the different steps of the project according to its objectives. Methodology includes sampling, characterization, the biomethane potential test and the pretreatment to improve methane production. Results chapter then presents results of characterization and both tests of biomethane potential. Finally, a technical and economic analysis is presented to evaluate the profitability of the project. Final recommendations indicate that anaerobic digestion of untreated sludge is not possible because of the lack of biogas production. Anaerobic digestion of treated sludge improves biogas production, but economic analysis shows that treatment would not be profitable according to the Celanese's economic criteria. The final chapter presents the alternative option to anaerobic digestion, which is pyrolysis. Results from a thermogravimetric analysis indicate that pyrolysis might be a promising solution. The general recommendation of this project if to evaluate pyrolysis of Celanese's sludge as a future alternative to anaerobic digestion.

The effects of starch and phosphorus (P) source on P partitioning and ruminal phytase activity were evaluated in eight lactating cows (113 DIM). Four cows were ruminaly cannulated. Cows were randomly assigned to treatments in a duplicated 4x4 Latin square with four, 18-d periods. Diets included dry ground corn (DG) or steam flaked corn (SF), with a no supplemental P (low P diet; 0.34% P) or supplemental purified phytic acid (PA; 0.45% P) to provide additional P from an organic source. Total collection of milk, urine, feces, and feed were sampled each period, while rumen fluid was sampled on d 18. Excretion of feces, urine, P, and N was lower in cows fed SF than in cows fed DG. Milk yield was unaffected by diet despite a lower DMI by cows fed SF. Cows fed SF tended to have a higher feed efficiency and lower milk urea nitrogen (MUN) concentration than cows fed DG. Rumen pH was unaffected by diet, but milk fat content was lower for cows fed SF. Milk yield, DMI, and feed efficiency were not affected by PA. Cows fed PA had increased P intake and excretion, but a lower milk P as a percentage of intake compared with cows fed the low P diet. An interaction of starch source and P source was observed for ruminal phytase activity. Altering dietary sources of starch and P offers opportunity to improve P availability and reduce manure nutrient excretion. / Master of Science

Temperature-phased anaerobic digestion (TPAD) has become increasingly appealing in recent years due to the pathogen destruction capabilities of the system. However, there has also been concern about the dewatering properties of the sludges created by these systems. A laboratory study was conducted at Virginia Tech to determine the effect of thermophilic solids retention time (SRT) on sludge dewatering properties, to characterize system parameters associated with dewatering, and to understand the mechanisms causing changes in dewatering properties between the thermophilic and mesophilic phases. The study showed that while anaerobic digestion caused dewatering properties to deteriorate, sludges varied little with thermophilic SRT. Acidogenesis was essentially complete after 1.5 days. Subsequent mesophilic digestion resulted in little change to dewatering properties and modest reductions in conditioning doses, but substantial reductions in biopolymer (protein + polysaccharides) occurred. It appears that thermophilic anaerobic digestion creates or releases colloidal materials that cause dewatering to be poor and subsequent mesophilic digestion for 15 days does little to improve sludge properties of TPAD systems. / Master of Science

This study aims to provide the latest understanding of cutting-edge technologies that enable wastewater organic carbon diversion and recovery through the enhancement of sludge production and blending, digestibility, dewaterability, and dewatered cake odor emission control. A comprehensive literature review showed that iron-based coagulants tend to show less negative impact than aluminum-based coagulants. This can be attributed to the reduction of ferric to ferrous ions in the course of anaerobic digestion (AD), which leads to a suite of changes in protein bioavailability, alkalinity, and hydrogen sulfide levels, and in turn the sludge dewaterability and odor potential. In terms of the roles of thermal hydrolysis pretreatment (THP), the mechanism review indicated that the improvement of sludge dewaterability and anaerobic digestibility as a result of THP was because of the destruction of extracellular polymeric substances and increase of hydrolysis rate. However, THP also brings side effects such as high free residual ammonia and recalcitrant dissolved organic nitrogen (rDON) in the effluent. Besides, a comprehensive understanding of the formation of the odorous compounds in the sludge treatment processes indicated that sulfurous and nitrogenous compounds are usually regarded as the major odor-causing substances. A Pilot THP-AD study indicated that adding aluminum to produce primary sludge can improve overall plant sludge digestibility, dewaterability, and well as the rDON reduction. Moreover, results from a pilot THP-AD and biochemical methane potential (BMP) test study indicated that adding a secondary thermal hydrolysis after a primary thermal hydrolysis-AD system can still create new BMP. Finally, a pilot study was conducted to evaluate the effect of aeration in the sludge holding tank on biosolids odor emission. The two rounds of bench-scale aeration studies indicated that aerating the sludge in holding tanks reduced peak emission concentrations of sulfurous odorous compounds. Further full-scale validation confirmed that aeration can be used by utilities as a simple means for biosolids odor control. / Doctor of Philosophy / Public wastewater treatment annually consumed 3-4% energy production and contributed 1% greenhouse gas emission in the U.S. Meanwhile, the chemical energy contained in wastewater was estimated to be 9.3 times the energy it takes to treat it. Therefore, harvesting wastewater energy is proposed as a viable means for achieving energy and carbon neutral wastewater treatment. The approach to sending wastewater energy as much as possible to anaerobic digesters in which microorganisms help harvest useful energy in the form of flammable methane was evaluated in this study. From literature, we learned that chemicals used for upstream wastewater energy capture and nutrient removal may make the downstream energy recovery difficult. While, thermal hydrolysis pretreatment, an industrial-scale pressure cooker, can be used to improve the ease of microbial bioenergy harvesting by making organics more biodegradable. However, thermal hydrolysis may also bring side effect in terms of recalcitrant organic formation. Also, in the course of energy recovery, the production and emission of nuisance odor may occur but can be controlled. Building on this existing knowledge, this study evaluated the pros and cons of the approach to using chemicals to capture and recover energy from wastewater. The results showed that the extents of energy recovery and savings was greater than the compromised solids reduction from the process. Moreover, results from a biochemical methane potential test study indicated that adding a secondary thermal hydrolysis can recover even more chemical energy from wastewater. In the end, a pilot study was conducted to develop a simple and economical approach to mitigating the odor emission issue during sludge handling. Results showed that pumping air into the sludge holding tank can substantially reduce peak odor emission. This approach was later verified in a full-scale test and recommended to utilities as a simple means for biosolids odor control.

Washington D.C. Water and Sewage Authority is planning to construct a new anaerobic digestion facility at its Blue Plains WWTP by 2008. The research conducted in this study is to aid the designers of this facility by evaluating alternative digestion technologies. Alternative anaerobic digestion technologies include thermophilic, acid/gas phased, and temperature phased digestion. In order to evaluate the relative merits of each, a year long study evaluated the performance of bench scale digestion systems at varying solids retention times (SRT) and organic loading rates (OLR). The digesters were fed a blend of primary and secondary residuals from the Blue Plains wastewater treatment facility. In each study phase, temperature phased anaerobic digestion was compared to single stage mesophilic digestion (the industry standard) at the same SRT. Single stage thermophilic digestion was evaluated by sampling the first thermophilic stage of the temperature phased digestion systems throughout the study. Additionally, the first phase study compared acid/gas phased digestion to temperature phased and single stage mesophilic digestion. Results of the study demonstrated that the temperature phased digestion system consistently performed better than the other systems during each study phase by having higher volatile solids reduction (VSR), higher methane production, and lower residual biological activity. The highest observed VSR during the study (67%) occurred in a temperature phased digestion system operated at 7.5 days in each stage. Based on these results, it seems a suitable candidate for the Blue Plains digestion facility. Additionally, odor studies performed in conjunction with the research presented in this paper have shown distinct advantages for the temperature phased process. / Master of Science

Today's society is facing major challenges. In order to reduce the climate impact fossil fuels should be replaced with fuels that do not contribute to the greenhouse effect. The growing population generates organic waste originating from industry and households so called organic fraction of municipal solid waste (OFMSW). Through anaerobic digestion, waste can be utilized to produce energy-rich methane gas. In this way, waste can be a resource instead of a burden on society. The purpose of this project is to investigate the methane yield of source-sorted organic fraction of municipal solid waste (SS-OFMSW) pretreated with screw crush technology and methane yield at the co-digestion of food waste and biosludge from paper mills. SS-OFMSW which is either pre-treated in a screw crusher or a Food Waste Mill and a mixture of SS-OFMSW and biosludge from paper mills digested in a semi - continuous wet process under mesophilic conditions with a retention time of 20 days. Screw crush technique gave a slurry with a methane yield of about 440-490 mL / g VS, which was slightly higher than the yield of 300-350 mL / g VS from the slurry pretreated with Food Waste Mill. The methane concentration was slightly higher for slurry pretreated with Food Waste Mill, 74% in average compared with 68% for slurry pretreated with screw crush. Biosludge from paper mills is an organic waste that can be digested in order to produce biogas. The sludge is poor in nutrients and methane yield at individual anaerobic digestion of paper mill sludge is relatively low. In this study, biosludge was co-digested with SS-OFMSW. The mixture with the proportions 1:1 by g VS gave a methane yield of about 420-480 mL / g VS which is higher than the constituent substrates digested separately. Co-digestion gave a methane concentration at 80% which is also higher than at the individual anaerobic digestion of substrates.

Anaerobic digestion is a sustainable and economically feasible waste management technology, which lowers the emission of greenhouse gases (GHGs), decreases the soil and water pollution, and reduces the dependence on fossil fuels. The present thesis investigates the anaerobic digestion of waste from food-processing industries, including citrus wastes (CWs) from juice processing and chicken feather from poultry slaughterhouses. Juice processing industries generate 15–25 million tons of citrus wastes every year. Utilization of CWs is not yet resolved, since drying or incineration processes are costly, due to the high moisture content; and biological processes are hindered by its peel oil content, primarily the D-limonene. Anaerobic digestion of untreated CWs consequently results in process failure because of the inhibiting effect of the produced and accumulated VFAs. The current thesis involves the development of a steam explosion pretreatment step. The methane yield increased by 426 % to 0.537 Nm3/kg VS by employing the steam explosion treatment at 150 °C for 20 min, which opened up the compact structure of the CWs and removed 94 % of the D-limonene. The developed process enables a production of 104 m3 methane and 8.4 L limonene from one ton of fresh CWs. Poultry slaughterhouses generate a significant amount of feather every year. Feathers are basically composed of keratin, an extremely strong and resistible structural protein. Methane yield from feather is low, around 0.18 Nm3/kg VS, which corresponds to only one third of the theoretical yield. In the present study, chemical, enzymatic and biological pretreatment methods were investigated to improve the biogas yield of feather waste. Chemical pretreatment with Ca(OH)2 under relatively mild conditions (0.1 g Ca(OH)2/g TSfeather, 100 °C, 30 min) improved the methane yield to 0.40 Nm3/kg VS, corresponding to 80 % of the theoretical yield. However, prior to digestion, the calcium needs to be removed. Enzymatic pretreatment with an alkaline endopeptidase, Savinase®, also increased the methane yield up to 0.40 Nm3/kg VS. Direct enzyme addition to the digester was tested and proved successful, making this process economically more feasible, since no additional pretreatment step is needed. For biological pretreatment, a recombinant Bacillus megaterium strain holding a high keratinase activity was developed. The new strain was able to degrade the feather keratin which resulted in an increase in the methane yield by 122 % during the following anaerobic digestion. / <p>Akademisk avhandling som för avläggande av teknologie doktorsexamen vid Chalmers tekniska högskola försvaras vid offentlig disputation den 1 juni 2012, klockan 10.00 i KA-salen, Kemigården 4, Göteborg.</p>