Anaerobic digestion is a useful method for stabilizing and reducing the waste activated sludges (WAS) produced from biological secondary treatment. Pretreatments can make anaerobic digestion more efficient. However, the study of anaerobic digestion and pretreatments is limited to a focus in treating conventional WAS. Therefore, WAS from three non-conventional municipal wastewater treatment systems, a rotating biological contactor (RBC), a lagoon, and a moving bed bioreactor (MBBR), were digested anaerobically to determine the sludges’ biogas potentials compared to a conventional WAS. All three WAS had lower biogas potential normalized per volatile solids than conventional sludge by 46% + 6 (MBBR), 63% + 6 (RBC), and 77% + 7 (lagoon). The four sludges were pretreated with ultrasonic energies of 800 - 6550 kJ/kg TS to illustrate impact of sludge type on biogas production, solubilization, and digestion kinetics. All four sludge types responded uniquely to the same levels of sonication energies. The greatest increase in biogas production over the control of pretreated sludge did not coincide consistently with greater sonication energy but occurred within a solubilization range of 2.9 – 7.4% degree of disintegration (DD) and are as follows: 5% + 3 biogas increase for conventional sludge, 12% + 9 for lagoon, 15% + 2 for MBBR and 20% + 2 for RBC. The yield of biogas production related to soluble COD decreases with increased sonication energy. Hence it is likely that sonication produces refractory COD or causes inhibition in biogas production. The effect of sonication on digestion kinetics was inconclusive with the application of Modified Gompertz, Reaction Curve, and First Order models to biogas production. Diauxic growth patterns of biogas production of sonicated conventional waste demonstrates that the active time of digestion can be decreased through the conversion of less preferential substrates into existing, preferential substrates.

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

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.

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

This study evaluates the enhancement of anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) by microwave pretreatment (MW) at high temperatures (115, 145 and 175°C). The highest level of solubilization was achieved at 175ºC, with a supplemental water addition of 30% (SWA30). Pretreatments combining two modalities; MW heating in presence or absence of hydrogen peroxide (H2O2) was also investigated. Biochemical methane potential (BMP) tests were conducted on the whole OFMSW, as well as on the liquid fractions. The whole OFMSW pretreated at 115 and 145 ºC showed little improvement in biogas production over control. When pretreated at 175 ºC, biogas production decreased due to formation of refractory compounds, inhibiting digestion. For the liquid fraction of OFMSW, the effect of pretreatment on the cumulative biogas production (CBP) was more pronounced for supplemental water addition of 20% (SWA20) at 145 ºC. Combining MW and H2O2 modalities did not have a positive impact on OFMSW stabilization and enhanced biogas production. Based on the BMP assay results, the effects of MW pretreatment (145 ºC) on the AD of OFMSW (SWA20) were further evaluated in single and dual stage semi-continuous digesters at hydraulic retention times (HRTs) of 20, 15, 12 and 9 days. Overall, MW pretreatment did not enhance the AD of the whole waste at the HRTs tested. However, the use of a dual stage reactor digesting non pretreated whole OFMSW had the best performance with the shortest HRT of 9 days. Conversely, for free liquid after pretreatment in two stage reactors at 20 day HRT methane production was tripled. In general, the performance of the dual stage digesters surpassed that of the single stage reactors. Cyclic BMP assays indicated that using an appropriate fraction of recycled effluent leachate can be implemented without negatively effecting methanogenic activity and biogas production. Based on the results obtained in this study, digestion of OFMSW by dual stage reactors without pretreatment appears to provide the best potential for waste stabilization in terms of biogas production and yield, process stability and volumetric loading rates.

Anaerobic digestion of waste activated sludge can be improved if hydrolysis of particulate substrates is enhanced and available substrate is made more accessible by both breakup of the sludge matrix floc and rupture of the cell wall. Microwave (MW) pretreatment was suggested and studied as a way to improve digestion efficiency. The work done focuses on the effects of MW pretreatment on the characteristics of the sludge, due to thermal and athermal effects. It also evaluates the effects some process variables in the activated sludge process have on the pretreatment efficiency as well as the effect operating conditions in the downstream anaerobic digestion process have on the biodegradability efficiency of those sludges. Effects of athermal and thermal MW radiation were measured by use of a customized MW oven capable of providing MW radiation with uncoupled thermal and athermal effects. Athermal radiation was capable of increasing substrate present in the soluble phase of sludge, and had a positive effect in the digestion of athermal samples. The increases in biogas production and substrate solubilisation were smaller in magnitude than the increases measured for MW thermal tests. Further refining of the tests with athermal and thermal sludge, involved separation by size class of the solubilized substrate by means of ultrafiltration (UF), and revealed that changes in particle size distribution were significant not only for MW thermal tests, but also for athermal tests, with a particular emphasis in proteins in athermal tests. These changes had an effect on the biodegradability of the sludges by class size, with thermally pretreated sludge producing more biogas for smaller particles size classes but also exhibiting more inhibition. Tests were made with several combinations of sludge with different ages and subject to different MW pretreatment temperatures. The work showed that sludge age or solids retention time (SRT) has a significant effect on the pretreatment efficiency with maximum biogas improvements measured at different MW pretreatment temperatures depending on the SRT of the sludge tested, and with different behaviour for mesophilic and thermophilic digestion. Mesophilic tests showed greater improvements in terms of digestion effiency on average, but thermophilic tests showed more uniform performance, with a higher baseline efficiency. The presence of an optimum of MW pretreatment temperature and sludge SRT for maximal biogas production is more defined for mesophilic conditions than for thermophilic conditions. Semi-continuous studies were conducted with several combinations of single and two stage mesophilic and thermophilic digestors treating MW pretreated sludge and non-pretreated sludge. Staging and thermophilic digestion allowed the maintenance of a stable digestion process with high biogas productions and high solids removal efficiencies with production of sludge with good bacteriological characteristics for an very low residence time (5 d).

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.