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Sludge management is the highest operating cost in municipal wastewater treatment. Anaerobic digestion (AD) is used to stabilize the sludge and reduce biosolids generation. Hydrolysis kinetics limit the rate of anaerobic digestion and must be improved to increase the overall process rate. In this study a new sludge characterization analysis was used to evaluate hydrolysis in a lab-scale pretreatment process operated at 55℃, 65℃, and 75℃. The experimental results were used to develop a new AD mathematical model, the hydrolysis digestion model (HDM). The model developed is easier to use, as the number of processes and variables were reduced by half, in comparison to existing models. The model variables can be measured using standard sludge characterization analysis, and the hydrolysis reactions included the fermenting microorganism to more accurately model the two-phase hydrolysis model. Model simulations were found to be a good fit of the experimental results, accurately predicting the rate and extent of hydrolysis in the pretreatment digester. / Thesis / Master of Applied Science (MASc)

Organosilicon compounds, which are heavily utilized in personal care products, are typically present, sometimes in high concentrations in the influent of wastewater treatment facilities. During anaerobic sludge digestion, these compounds volatilize and enter the methane gas recovery stream. As the methane is combusted for energy cogeneration, these compounds become oxidized to microcrystalline silicon dioxide and cause damage and potential failure of expensive infrastructure. Adsorption and other catchment methods are typically utilized for removal of these volatilized compounds in order to mitigate their entrance into methane combustion systems. This research investigated the effect of phased anaerobic digestion, specifically acid-gas digestion, on the behavior of the volatilization of these organosilicon compounds, particularly octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) as these are the most abundant volatile silicone compounds present in sludge. A bench scale acid reactor anaerobic digester was operated at varying solids retention times and temperatures in order to quantify biogas effects generated in the downstream gas reactor, which was operated at a constant mesophilic conditions. Results of the research indicated that the addition of an acid reactor did not cause a change in behavior of the D4 and D5 siloxane volatilization in the downstream gas reactor. However, it was observed that hydrogen sulfide gas was decreased in the gas reactor when an acid reactor was utilized, which could permit decreased corrosivity of biogas recovery. Cumulative volatile solids reduction and gas reactor methane yield data did not indicate an enhancement due to utilization of acid-gas digestion. / Master of Science

Call number: LD2668 .T4 1979 G46 / Master of Science

Energy shortfall and air pollution are some of the challenges the human kind is facing today. Fossil fuel is still the most widely used fuel, which is a non-renewable resource, increasing excess carbon dioxide into the air. To overcome these issues, and reduce the carbon footprint, a greater development of renewable energy from green and natural resources is required. Compared to fossil energy, renewable energy has the benefit to reduce greenhouse gas emissions. There are different solutions available for green and renewable energy. Biomass is all biologically produced matter. Through the biological breakdown of biomass, biogas can be produced through the process called anaerobic digestion. This work was focused on the production of biogas, using algal biomass, sewage sludge and coffee grounds in an anaerobic co-digestion system. The main goal of this study was to investigate the feasibility of combining these three substrates. Two different types of algae were employed; Chlorella vulgaris and Scenedesmus sp. and the investigations included even the cultivation and harvesting of algal biomass. The production of biogas was examined under anaerobic conditions using 5 batch reactors in duplicate under constant temperature of 37 °C in 30 days. The result showed that co-digestion of algal biomass with sewage sludge led to an enhanced biogas production by 75 % compared to that of just sewage sludge. This indicates the synergistic effects of co-digestion. However, the addition of coffee ground to the mixture lowered the biogas production. All mixtures except the two with coffee grounds were in neutral pH. Methanogens, involved in the last step in biogas production are very sensitive to pH, and pH around 7 is the optimal for their activity. Furthermore, the presence of caffeine in the coffee ground could also inhibit the biogas production.

Innovative pre-treatment methods applied to anaerobic digestion (AD) have developed to enhance the methane yields of food waste. This study investigates hydrodynamic cavitation, which induce disintegration of biomass through microbubble formations, impact on food waste solubilisation and methane production during following AD. Two different sub-streams of food waste (before and after the digestion) pre-treated by hydrodynamic cavitation were evaluated in lab scale for its potential for implementation in a full scale practise. First, the optimum condition for the hydrodynamic cavitation device was determined based on the solids and chemical changes in the food waste. The exposure time was referred to as the number of cycles that the sample was recirculated through the cavitation inducer’s region. The optimal cycles were later tested as a pre-treatment step in a BMP test and semi-CSTR lab scale operation. The tests showed that sufficient impact from the hydrodynamic cavitation was achieved by 20 cavitation cycles. Due to the pre-treatment, food waste solubilisation increased, up to 400% and 48% in terms of turbidity and sCOD measurements, respectively. In the BMP test, the treated samples improved the methane yield by 9-13%, where the digested food waste increased its kinetic constant by 60%. Fresh food waste was then processed in the semi-CSTR operation and the methane yield was increased by up to 17% with hydrodynamic cavitation for two reference periods. These promising results suggest that the hydrodynamic cavitation can be implemented for full scale production with food waste.

The Best PhD Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,1993-1995 / published_or_final_version / Civil and Structural Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

L'objectif de l'étude était d'analyser l'impact relatif des phénomènes physiques, biologiques et biochimiques sur le déterminisme de l'ingestibilité et la digestion des fourrages tropicaux. Les hypothèses de travail étaient que : 1) valorisés à des stades physiologiques assez précoces, l'ingestibilité et la digestion des fourrages tropicaux pouvaient être significativement améliorées, 2) la capacité cellulolytique du rumen ne serait pas le premier facteur limitant l'ingestibilité et la digestion des fourrages, 3) la résistance à la mastication et en conséquence la vitesse de réduction de taille des particules alimentaires (comminution) serait le premier facteur limitant l'ingestibilité. Dans un premier temps, une méta-analyse des données de la littérature a été réalisée. Dans un deuxième temps, 2 groupes d'expérimentations ont été menés afin: 1) de définir les conditions d'étude du deuxième groupe expérimental, 2) de valider nos hypothèses de travail. Les résultats de la synthèse bibliographique ont confirmé que les fourrages tempérés étaient significativement mieux ingérés que les fourrages tropicaux (68.70 vs 57.83 g/PM ; P<0.001). De plus, la méta-analyse a mis en évidence que le travail masticatoire fourni pour valoriser 1kg de MS de fourrage tropical était deux fois plus important qu'avec un fourrage tempéré. Les résultats des expérimentations à but « méthodologique » ont prouvé : 1) l'efficacité de l'apport d'une mixture d'enzyme fibrolytique exogène (dégradabilité 24h d'un fourrage haché de 56j : 32.14 vs 39.25% en absence ou en présence d'enzyme, respectivement; P<0.0001) ; 2) que certains paramètres digestifs et ingestifs étaient différents selon la fréquence des repas (contenu total ruminal avec un fourrage de 21j : 1.01 vs 0.77 g/g MSI avec 4 ou 2 repas / jour, respectivement; P<0.001) ; 3) que certains paramètres digestifs et ingestifs étaient différents selon la période du nycthémère (index de mastication avec un fourrage de 56 jours : 1.07 vs 1.52 durant la période diurne ou nocturne, respectivement; P<0.05). Ainsi au cours du deuxième groupe expérimental, l'étude des dynamiques digestives a été réalisée en distribuant 2 repas par jour, les mesures ont été effectuées sur le nycthémère et l'étude en condition enzymatique non limitante, a été effectuée en apportant de l'enzyme fibrolytique exogène. Les résultats du 2ème groupe expérimental ont montré que 1) l'ingestibilité et la digestibilité diminuaient significativement avec le vieillissement du fourrage (MSI était de 86.69, 83.10, 69.37, 59.29, 50.60 g/PM respectivement pour les fourrages âgés de 14, 21, 28, 42 et 56 jours ; P<0.02) ; 2) l'ingestibilité n'était pas fonction de l'activité cellulolytique (P>0.4) ; 3) l'ingestibilité était inversement proportionnelle à l'index de mastication (MSI (g/PM)= 125 - 65.3 IdMast ; P<0.03). En conclusion, il apparaît que les jeunes fourrages tropicaux (<28j) présentent de bonnes valeurs nutritives, que le potentiel cellulolytique ne serait pas le premier facteur limitant l'ingestibilité, et qu'il s'agirait plutôt de la vitesse de communition. L'impact important de la variabilité individuelle sur l'ingestibilité, observé au cours de nos expérimentations, reste à confirmer.

Two studies were performed to investigate the ability of a portable near-infrared spectrophotometer (NIRS) for on-site analysis of nutrient components in feces from cattle. In trial 1 of study 1, growing dairy steers were fed diets containing either 86 or 90% concentrate. Regression values from a calibration set of 56 samples were promising for CP, DM, and NDF, but not for ADF or starch. In trial 2 of study 1, finishing dairy steers were fed diets containing either thick (512 g/L) or thin (460 g/L) steam-flaked corn. Regression values from a calibration set of 126 samples were poor for all nutrients. Both studies showed statistically valid NIRS calibrations, but further validation was required to make regression values acceptable (R² > 0.80) for all fecal nutrient components. In study 2, NIRS analysis was employed on novel research. Young dairy bull calves were fed diets containing either whole or steam-flaked corn from pre-weaning until 8 weeks post-weaning when the first animal was heavy enough for inclusion into a commercial feedlot. Again, although statistically valid, regression values from a calibration set of 220 samples were promising for CP and ADF, but not predictive for DM, NDF, ash, and starch. Growth performance parameters were similar between diets, with starch digestibilities diverging after weaning and changing to a Holstein starter diet. These 2 studies show that commercial and research application of a portable NIRS for on-site analysis of the nutrient composition of feces from young, growing, and finishing dairy steers statistically possible but requires further validation research. Also, results from the second study imply that there is no advantage in feeding steam-flaked corn to dairy calves from pre-weaning to 8 weeks post-weaning or until reaching feedlot weight. However, starch digestibility begins to improve for steam-flaked corn to whole corn once the animal has been weaned.