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.

Reproduction de : Thèse de doctorat : Qualité et sécurité des aliments : Toulouse, INPT : 2006. / Titre provenant de l'écran-titre. Bibliogr. 337 réf.

Includes bibliographical references (p. 62-73).

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 170-181). Also available in electronic version. Access restricted to campus users.

Anaerobic digestion of agricultural wastes provides an opportunity for renewable energy production while reducing emissions of greenhouse gasses such as carbon dioxide and methane from crop and livestock production. While anaerobic digestion is possible under a wide range of temperatures and reactor configurations, it does require a stable methanogenic community composed of hydrolytic and fermentative bacteria and methanogenic archaea in order to maintain robust methane production. Research focused on characterizing and optimizing the microbial community during anaerobic digestion is increasingly exploiting DNA-based methods. In addition to providing an in-depth phylogenetic survey, these techniques permit examination of dynamic changes in α- and β-diversity during the digestion process and in response to perturbations in the system. This study used universal target amplification, next generation sequencing, and quantitative PCR to characterize the Bacteria and Archaea in digestate from thermophilic batch anaerobic digesters processing different combinations wheat ethanol stillage waste and cattle manure. The results indicated that the bacterial community was composed primarily of Firmicutes, with Proteobacteria and Bacteroidetes also numerically abundant. While less phylogenetically diverse, the archaeal community showed robust populations of both hydrogenotrophic and acetoclastic methanogens. A core microbiome present across all reactors was identified and differences in the relative abundances of the bacteria within the core community suggested significant niche overlap and metabolic redundancy in the reactors. A time-course study correlating the abundances of individual Bacteria and Archaea to methane production and volatile fatty acid catabolization identified several microorganisms hypothesized to be critical to both hydrogenotrophic and acetoclastic methanogenesis. Individual Bacteria most closely related to Clostridium spp. and Acetivibrio spp. were 10-1000-fold less abundant in reactors suffering from volatile fatty acid accumulation and inhibition of methanogenesis. Additionally, failing reactors were devoid of robust populations of acetoclastic methanogens. Microorganisms identified as critical during the time-course study were targeted for isolation in vitro and a robust methanogenic consortium consisting of at least 9 bacteria and both a hydrogenotrophic and an acetoclastic methanogen was stably propagated. Addition of this bioaugmentation consortium to digesters experiencing classic symptoms of acid crisis resulted in reduced acetate accumulation and initiation of methanogenesis. One acetoclastic methanogen, most likely a novel species from the genus Methanosarcina, showed particularly robust growth in the recovered bioaugmented reactors, increasing 100-fold in the first 7 days post-treatment. A combination of Illumina shotgun and Roche 454 paired-end sequencing chemistry was used to generate a high quality draft genome for this organism. Analysis of the annotated genome revealed diverse metabolic potential with a full complement of genes for acetoclastic, hydrogenotrophic and methylotrophic methanogenesis pathways represented. Taken as a whole, this thesis provides the foundation for using microbial community characterization to inform anaerobic digester design and operation. By identifying organisms of interest, correlating their abundance to specific biochemical functions and confirming their hypothesized functions in situ, microorganisms critical for robust methane production were acquired. The logical extension of this work is to establish monitoring tools for microorganisms identified as critical to specific performance parameters, to enumerate them in real-time, and to use that data to improve reactor operation.

Today 88 % of the world energy comes from fossil fuels. Greenhouse gas emissions are increasing and the fossil fuels energy sources will decrease at some point. Other alternatives must be found, to substitute and lower the usage of fossil fuels. Biogas is one of these other options. It is a versatile fossil free fuel that can be used for heat, power and fuel for vehicles. Many different substrates have been used for biogas production over the years, and now algae are examined as a substrate. Algae have advantages over the former substrates used for biogas production. Laboratory experiments were conducted to examine the co-digestion potential of algae and biosludge, which is a rest product from a wastewater treatment plant at a pulp and paper mill. The profitability aspect of using algae and biosludge for biogas production has been examined as well.The result shows that unmixed algae were the highest methane producing substrate, which produced a maximum of 203,5 Nml/g VS. An interesting result was that both algae and biosludge separately produced more methane gas than the mixtures. The profitability aspect of the thesis showed that it is not profitable to use algae primarily for biogas production, based on the conditions of today.

The effects of a simulated in vitro digestion model on the viscosity of solutions of locust bean gum, guar gum, fenugreek gum, xanthan gum, gum Arabic, psyllium, flaxseed gum and soy soluble polysaccharides (SSPS) were examined in this study. All hydrocolloid solutions were formulated for low viscosity (LV), medium viscosity (MV) and high viscosity (HV), which were subsequently subjected to 3 treatments of equal volumes each. The treatments consisted of 1) H2O-dilutions, 2) acid and alkali in the absence of enzymes/bile and 3) an in vitro digestion model simulating the gastric and duodenal phases with pH changes in the presence of hydrolytic enzymes and bile salts. All hydrocolloids showed substantial reductions in viscosity, with dilutions exerting the greatest effect. Depending on the concentration, xanthan gum retained 20-50% of its initial viscosity while the other solutions were in a lower range of 1-16%, thereby showing considerable resilience to the 3 simulated conditions. / NSERC

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.

Access to modern energy is essential to achieve sustainable development and poverty reduction. However, with about 321 kWh per capita, Rwanda is ranked among the countries that have a lower consumption of primary energy in the world. More than 86 percent of its total energy comes from the traditional biomass energy such as forests, agricultural residues and by-products from crops that lead to environmental degradation and ecological imbalance and negative impacts on human health as well. In addition, only 301,500 ha of forest are available for fuel wood and other uses such as construction for a total population of 10.5 million. Therefore, decentralized energy sources in small-scale are presented to improve access to "appropriate" energy, which are beneficial to human health and environmental perspectives. The anaerobic digestion of biomass, popularly called “biogas”, is one of the appropriate energy technologies for cooking and/or lighting purposes (both in households and in institutions), which receives special attention in Rwanda since 2007. Three main objectives of this study were to assess the current biogas sector in Rwanda, to make projections of biogas development by 2020 and finally to analyze the socio-economic and environment benefits of biogas use to the Rwandan community. The fieldwork conducted in two districts per province in addition to services that are in the capital, was based on the structured questionnaire, discussion with key people and see the state of biogas built. Therefore, in this study we used the "Appropriate Energy Model” to measure the degree of biogas dissemination, which educates for “geographical, institutional, entrepreneurial and socio-cultural “aspects. The results showed that the temperature conditions in the country are generally conducive to the operation of a digester. However, the drought period between June and August, water scarcity in some regions and a low potential for digester feeding impede the propagation of biogas to a large number of people.  The Rwandan entrepreneurs do not face institutional barriers to start-up biogas companies since the bureaucratic system in registration of a company is transparent. The installation costs of biogas plant are so high that they hamper the dissemination of biogas; however biogas technology does not contradict the socio-cultural conditions of Rwandans. Based on projections of potential biogas in Rwanda in 2020, following three scenarios for 2020 biogas development were identified: 1,135,000 biogas plants can be built in 2020 by considering a global basis the potential biogas available If 70% of the population will live in grouped settlements in 2020, 70% of Rwandan households will use biogas if additional resources as livestock and subsidies were provided to the poor families. Only 10% of the population (251,000households) will be eligible for biogas installation Reducing the consumption of firewood after biogas operation provides annual coverage of approximately 0.306 ha of forest area per household. Therefore, each household biogas would reduce annual GHG emissions of about 4.1 tonnes of CO2 and could possibly lead to Rwanda an annual income of about USD 21 due to the reduction of CO2 emissions in a hypothetical rate USD 5 per ton of CO2 if registered under the CDM.