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.

Several operational and environmental conditions can result in poor biogas yield during the operation of anaerobic digesters and anaerobic bioreactor landfills. Over time, anaerobic co-digestion and leachate blending have been identified as strategies that can help address some of these challenges to improve biogas production. While co-digestion entails the co-treatment of multiple substrates, leachate blending involves combination of mature and young landfill leachate. Despite the benefits attributed to these strategies, their impact on recirculating bioreactor landfill scenarios and anaerobic digesters requires further investigation. In the first phase of this thesis, an attempt to assess biogas production improvement from organic fraction of municipal solid waste in simulated bioreactor landfills through recirculation of blended landfill leachate was conducted. Real old and new leachate blends (67%New leachate:33%Old leachate, 33%New leachate:67%Old leachate) as well as 100%New and 100%Old leachate were recirculated through six laboratory-scale bioreactors using open-loop and closed-loops modes. Compared with the control bioreactor where 100% new leachate was recirculated and operated as a closed-loop, cumulative biogas production was improved by as much as 77 to 193% when a leachate blend of 33%New:67%Old was recirculated. Furthermore, comparison of the results from open-loop and closed-loop operated bioreactors indicated that there was approximately 28 to 65% more biogas in open-loop bioreactors. The Gompertz model applied to the methane data produced a better fit (R2 > 0.99) than first order and logistic function models. Leachate blending reduced the lag phase by almost half and thus helps in alleviating the ensiling during the start-up phase. In the second phase, a biochemical methane potential (BMP) assay was conducted to investigate the synergistic effect of percentage sewage scum addition; 10%, 20% and 40% (volatile solids basis) on biogas production during mesophilic co-digestion with various organic substrates viz; organic fraction of municipal solid waste, old leachate, new leachate and a leachate blend prepared from 67%old leachate and 33%new leachate under sub-optimal condition. Results show that the net cumulative bio-methane yield was improved with increased sewage scum percentage during co-digestion because of positive synergism. Meanwhile, the addition of 40% sewage scum to the individual co-substrates improved net cumulative bio-methane yield by 28% - 67% when compared to their respective mono-substrate digestion bio-methane yield. Furthermore, reactors containing leachate blends consistently produced more biogas over other sets because of blending. Kinetic modelling applied to the bio-methane production data shows modified Gompertz equation achieved a better fit with up to an R2 value of 0.999. Finally, co-digestion substantially reduced the lag time encountered during mono-digestion. In the last phase, the biomethane potential involved in the ACo-D of sewage scum, organic fraction of municipal solid waste was investigated in this phase using either thickened waste activated sludge or leachate blend (67%old leachate and 33%new leachate) as a tertiary component. Compared to the mono-digestion of TWAS, results shows that biomethane yield was enhanced in by as much as 32 - 127% in trinary mixtures with SS and OFMSW mainly due to the effect of positive synergism. Furthermore, LB addition improved biomethane production in trinary mixtures of SS:LB: OFMSW by 38% than in corresponding trinary mixtures of TWAS. Whereas an optimal combination of 40%SS:10%TWAS:50%OFMSW and 20%SS:70%LB:10%OFMSW produced the highest biogas yield of 407mL.gVS-1 and 487mL.gVS-1 respectively. The application of the first order model showed that lower hydrolysis rates promoted methanogenesis with k = 0.04day-1 in both 20%SS:70%LB:10%OFMSW and 20%SS:50%LB:30%OFMSW. Estimations by the modified Gompertz and logistic function were conclusive methane production rate improved by as much a 60% in a trinary mixture over the production rate during mono-digestion of TWAS alone. The results of the various experiments of this thesis therefore suggest that leachate blending can be used as a strategy to improve biogas production in both bioreactor landfills and anaerobic digesters. Also, sewage scum as an energy-rich substrate can be better utilized during co-digestion with other low-energy substrates.

The Ontario biogas industry is relatively young and the overall objective of this research was to help support the growth of the industry with investigating the use of co-substrates and reactor design to enhance biogas production, recommend guidelines on the operation of full scale systems to optimize performance and characterize digestate quality. Laboratory studies evaluated the use of various substrates in the co-digestion with liquid dairy manure. These studies were used to establish ultimate biogas yields, % volatile solids (VS) reduction and minimum hydraulic retention times (HRTs). Box-Wilson Central Composite design models for corn thin stillage and waste grease (as co-substrates with dairy manure) suggest methane yields optimize with increasing proportion of the feed VS from co-substrates (constant total VS in all assays) and increasing temperatures; however, temperature had a great effect. Bench scale studies were conducted to determine a change in digester design to optimize biogas yields and increase digestate stability. A two-phase digestion system was implemented for co-digestion systems using thin stillage and waste grease with dairy manure, and methane yields showed to increase by over 22% when compared with single-phase systems. Based on current FIT contracts of 18 to 20¢/kWhe, the increased electricity and heat production could make the two-phase system economically attractive for producers. Organic loading rates (OLRs) over 4.4 g VS/L led to digester upset and OLRs of over 4.2 g VS/L·day are not recommended. On-farm anaerobic digester systems were studied for digester performance and digestate quality. Residual biogas potential (RBP) yields were effective at evaluating the stability of digestate and the U.K. PAS 110:2014 limit of 0.45 L biogas/g VS (28 days incubation) was assessed too lenient for the Ontario systems studied. A limit of 0.25 L biogas/g VS after 28 days of incubation or 0.45 L biogas/g VS after 60 days of incubation are recommended. VS reductions ranged from 56 to 76% and easily achieved the O. Reg. 267/03 regulated 50% VS reduction. E.coli and Salmonella were typically 1 to 3 logs CFU/100 mL lower than raw manure and increased HRT did not demonstrate a significant impact on the bacterial log reductions. Intermediate alkalinity (IA)/partial alkalinity (PA) proved to be a valuable tool in determining potential digester upset and has been recommended as a standard performance parameter for on-farm systems.

Two different sludge pretreatments were investigated in an attempt to improve the management and performance of processes for the co-digestion of biosolids with fats, oils, and grease (FOG). The mechanisms of long chain fatty acids (LCFA) degradation in thermal hydrolysis pretreatment and the influence of pH on LCFA degradation in two-phase co-digestion systems were studied. LCFA thermal hydrolysis was investigated at different temperatures (90-250 °C) and reaction times (30 minutes and 8 hours). Approximately 1% of saturated fatty acids were degraded to shorter chain fatty acids at 140 and 160 °C (8-hr thermal hydrolysis). Only 1% or less of unsaturated fatty acids were degraded from 90 to 160 °C (8-hr thermal hydrolysis). Little degradation (< 1%) of both saturated and unsaturated LCFAs was observed at a 30-min reaction time. Both groups of LCFAs were stable up to 250 °C (30-min hydrolysis). The use of chemical-thermal treatments was also investigated. Only unsaturated LCFAs, C18:1 and C18:2, were degraded when thermally hydrolyzed with hydrogen peroxide coupled with activated carbon or copper sulfate. Semi-continuous, acid-phase digesters (APDs) under different pH conditions were studied in order to understand the effects of pH on FOG degradation. Increases in soluble chemical oxygen demand (SCOD) were observed in all APDs. However, the APDs with pH adjustment appeared to perform better than the controls in terms of solubilizing organic compounds. Approximately 38% and 29% of total COD (TCOD) was solubilized, and maximum volatile fatty acid (VFA) concentrations of 10,700 and 7,500 mg/L TCOD were achieved at pH 6 and 7, respectively; It is useful to note that the feed sludge had a VFA concentration of 2,700 mg/L COD. Higher pH (6.0-7.0) showed less accumulation of LCFA materials and more soluble LCFAs in the APDs. This indicates that the lower pH in the APDs was most likely the cause of precipitation and accumulation of LCFAs due to saturation of unsaturated LCFAs. / Master of Science

La digestion anaérobie représente un des acteurs majeurs du développement durable et de l'économie circulaire dans le concept « des déchets à l'énergie ». Compte-tenu de la grande diversité des déchets organiques, son développement passe par l'optimisation de la co-digestion. D’où la nécessité de développer des outils simples pour caractériser les substrats et pour prédire les performances des digesteurs afin d'optimiser leur fonctionnement. Cette thèse porte sur la caractérisation de la biodégradation des substrats solides par digestion anaérobie et l'optimisation de leur co-digestion à l'aide d'une approche de modélisation simple. En premier lieu, un nouveau protocole pour la quantification du potentiel méthane en mode batch a été mis en œuvre, intégrant une phase d'acclimatation entre l’inoculum et le substrat. Ensuite, un modèle simple a été développé sur la base du fractionnement de la matière organique en trois sous-fractions. Cette approche a permis de développer une base de données incluant les cinétiques et les potentiels en méthane (BMP) de 50 substrats. En second lieu, des expériences de co-digestion de deux substrats solides ont été menées en mode semi-continu à une charge appliquée (cva) constante puis à des charges appliquées croissantes. Les rendements expérimentaux en méthane ont toujours été supérieurs aux valeurs des BMP des mélanges calculées à partir des BMP de chaque substrat, soulignant l'importance de la respiration endogène. Quatre modèles incluant la respiration endogène avec des hypothèses différentes ont été proposés et évaluées pour prédire la production de méthane brute de digesteurs semi-continus en utilisant les données des substrats (BMP et cinétiques) acquises en mode batch. Deux modèles pour lesquels la production expérimentale de méthane à des cva croissantes correspondait bien aux données modélisées ont été validés. L'approche de modélisation retenue a été ensuite appliquée à des mélanges plus complexes de 3 et 5 substrats ainsi qu’à des biodéchets. Enfin, la réponse d’un digesteur fonctionnant en mode de production flexible, c’est-à-dire recevant des surcharges organiques ponctuelles régulièrement a été également modélisée avec succès. L'approche de modélisation proposée fournit un outil simple, pouvant être utilisé par les bureaux d'études, les constructeurs et les exploitants d’unités de méthanisation pour l'optimisation des mélanges de co-digestion et de la cva à utiliser en mode continu. Cela doit permettre de réduire le risque de défaillance et d’optimiser la rentabilité des unités de co-digestion. / Anaerobic digestion represents one of the major actors of sustainable development and the circular economy in the concept of "Waste to Energy". Given the great diversity of organic waste, its development requires the optimisation of co-digestion. Hence, it is needed to develop simple tools to characterize substrates and predict digester performance in order to optimize their operation. This thesis focuses on the characterization of biodegradation of solid substrates by anaerobic digestion and optimization of co-digestion using a simple modelling approach. First, a new batch protocol was implemented to quantify the Biochemical Methane Potential (BMP), integrating an acclimatization phase between the inoculum and the substrate. Then, a simple model was developed based on the fractionation of organic matter into three sub-fractions. This approach has allowed to develop a database including kinetics and BMPs of 50 substrates. Second, co-digestion experiments of two solid substrates were conducted in semi-continuous mode at a constant organic loading rate (OLR) and then at increasing applied loads. The experimental methane yields were always higher than the BMP values of the mixtures calculated from the BMPs of each substrate, underlining the importance of endogenous respiration. Four models including endogenous respiration with different assumptions were proposed and evaluated to predict raw methane production from semi-continuous digesters using substrate data (BMP and kinetics) acquired in batch mode. Two models for which the experimental methane production at increasing OLR corresponded well to the modelled data were validated. The chosen modelling approach was then applied to more complex mixtures of 3 and 5 substrates and to bio-waste. Finally, the response of a digester operated in flexible production mode, i.e. receiving regular punctual organic overloads, was also successfully modelled. The proposed modelling approach provides a simple tool that can be useful to design offices, manufacturers and operators of co-digestion units for the optimisation of feed mixtures and OLR to be used in continuous mode. This should reduce the risk of failure and optimise the profitability of co-digestion units.

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>

Biogas production from organic materials can be used as a renewable vehicle fuel, provide heat and generate electricity and can thereby reduce the greenhouse gas emissions. This thesis focuses on the biogas production based on lignocelluloses. There is an abundant availability of lignocelluloses, constituting 50% of the total biomass worldwide. However, the biomass recalcitrance limits the microbial degradation as well as the biogas production from these types of materials. In the present work different pretreatment methods have been performed in order to decrease the biomass recalcitrance and improve the biogas production. Steam explosion pretreatment, together with the addition of sodium hydroxide and hydrogen peroxide, has been performed on lignocellulosic-rich paper tube residuals. The pretreatment has resulted in methane yields of up to 493 NmL/gVS, which is an increase by 107% compared with untreated material. Furthermore, the use of an organic solvent, N-methylmorpholine-N-oxide (NMMO), was evaluated as a pretreatment method for spruce (both chips and milled), rice straw, and triticale straw. The NMMO pretreatment resulted in 202, 395, 328, and 362 NmL CH4/g carbohydrates produced of these substrates, respectively, corresponding to an increase of between 400-1,200% compared with the untreated version of the same material. Moreover, the paper tube residuals have been co-digested with an unstable nitrogen-rich substrate mixture, mainly based on municipal solid waste. The addition of the lignocellulosic-rich paper tubes in a co-digestion process showed stabilizing effects and prevented the accumulation of volatile fatty acids with a subsequent reactor failure. Additionally, synergistic effects have been found leading to between 15-33% higher methane yields when paper tubes were added to the co-digestion process compared with the yields calculated from the methane potentials of the two substrates. Substrate characterization analysis can be used to study the changes on the lignocellulosic components after the pretreatment, relating the changes to the performance in the anaerobic digestion. Increased accessible surface area, measured by the Simons’ stain and the enzymatic adsorption methods, as well as decreased crystallinity, determined by using the Fourier Transform Infrared Spectroscopy, can all be linked to improved biogas production after pretreatment. Finally, the NMMO pretreatment on forest residues has been financially evaluated for an industrial scale process design. The base case that was evaluated simulated a case where pretreated forest residues were co-digested with the organic fraction of municipal solid waste to obtain optimal nutritional balance for the anaerobic digestion. This process has been found to be economically feasible with an internal rate of return of 20.7%. / <p>Akademisk avhandling som för avläggande av teknologie doktorsexamen vid Chalmers tekniska högskola försvaras vid offentlig disputation den 24 maj 2013, klockan 10.00 i KA,Kemigården 4, Göteborg</p>

Este trabalho apresenta uma avaliação da produção de metano em um reator anaeróbio operado em batelada sequencial com biomassa imobilizada em suporte inerte (AnSBBR) pela codigestão de vinhaça de cana-de-açúcar e soro de queijo em condições mesofílicas. A avaliação é realizada com base na influência da variação dos aspectos operacionais de estratégia de alimentação (batelada ou batelada alimentada), interação entre tempo de ciclo (8, 6 ou 4 h) e concentração afluente (5000, 3750 ou 2500 mgDQO.L-1), carga orgânica volumétrica aplicada (5, 7,5, 10 ou 15 gDQO.L-1.d-1) e temperatura (25, 30 e 35&#186;C) sobre a estabilidade e desempenho do sistema. O AnSBBR com recirculação da fase líquida e volume reacional de 3,0 L foi operado por 186 dias, sendo o afluente para todos os ensaios composto por 75 % vinhaça e 25 % soro (massa/volume) e suplementado com bicarbonato de sódio. Nas condições operadas, o sistema demonstrou flexibilidade quanto à estratégia de alimentação, porém a redução do tempo de ciclo e da concentração afluente, para a mesma carga, resultou em menores produções de metano. Por outro lado, o aumento da carga orgânica, até o valor de 15 gDQO.L-1.d-1, favoreceu o processo, aumentando o rendimento de metano por DQO removida e a produtividade. A redução da temperatura de 30 para 25 &#186;C resultou na queda do desempenho, porém às temperaturas de 30 e 35 &#186;C foram obtidos resultados similares. O melhor desempenho foi alcançado a uma carga aplicada de 15,27 gDQO.L-1.d-1, tempo de ciclo de 8 horas, operação em batelada alimentada e temperatura de 30 &#186;C. Nessas condições, o sistema atingiu remoção de DQO solúvel de 88,8 %, produtividade de metano de 208,5 molCH4.m-3.d-1 (equivalente a 4672 CNTP-mLCH4.L-1.d-1), rendimento de metano por DQO removida de 15,76 mmolCH4.gDQO-1 e composição de metano de 72% no biogás. O ajuste do modelo cinético demonstrou preferência pela rota hidrogenotrófica na metanogênese em todos os ensaios. Na aproximação em escala plena para o cenário de usina de etanol de cana-de-açúcar com produção de etanol de 150.896 m3.ano-1 foi estimada uma geração de energia de 25.544 MWh.mês-1. / This paper presents an assessment of the methane production in an anaerobic sequencing batch biofilm reactor (AnSBBR) by co-digestion of sugarcane vinasse and cheese whey at mesophilic conditions. The assessment is based on the influence of modifying the operational aspects of feed strategy (batch or fed-batch), interaction between cycle time (8, 6 or 4 h) and influent concentration (5000, 3750 or 2500 mgCOD.L-1), applied volumetric organic load (5, 7.5, 10 or 15 gCOD.L-1.d-1) and temperature (25, 30 and 35 &#186;C) over the system stability and performance. The AnSBBR with recirculation of the liquid phase and 3.0 L of liquid medium was operated for 186 days, with influent composition for all assays of 75 % vinasse and 25 % whey (mass/volume), also supplemented with sodium bicarbonate. At the operated conditions, the system showed flexibility with regards to the feed strategy, but the reduction of cycle time and influent concentration, for the same organic load, resulted in lower methane productions. On the other hand, increasing organic load, to the value of 15 gCOD.L-1.d-1, favored the process, increasing methane yield and productivity. Temperature reduction from 30 to 25 &#186;C resulted in performance loss, although at 30 and 35&#186;C it was achieved similar results. The best performance was achieved at an applied organic load of 15.27 gCOD.L-1.d-1, cycle time of 8 hours, fed batch operation and temperature of 30 &#186;C. The system achieved soluble COD removal efficiency of 88.8 %, methane productivity of 208.5 gCOD.L-1.d-1 (equal to 4672 STP-mLCH4.L-1.d-1), methane yield per removed organic matter of 15.76 mmolCH4.gCOD-1 and methane composition of 72% of the biogas. The kinetic model fit showed preference for the hydrogenotrophic route in the methanogenesis. At the full scale approximation considering a scenario with a sugarcane ethanol plant with ethanol production of 150,896 m3.year-1 it was estimated an energy production of 25,544 MWh.month-1.

Slaughterhouse waste (SB) has high potential to be utilized in anaerobic digestion due to its high protein and lipid content. However, these are also the limiting factors of system stability. Thus, co-digestion of slaughterhouse waste with other agro-industrial residues (manure (M), various crops (VC) and municipal solid waste (MSW)) was introduced in this study to overcome this problem. The main objective of the work was to determine the operating parameters and the methane yield in semi-continuous co-digestion of slaughterhouse waste with other agro-industrial waste streams. Four continuously stirring tank reactors (CSTRs) with different substrates and mixtures (SB, SB:M, SB:VC and SB:VC:MSW) were started up operating with hydraulic retention time (HRT) of 25 days in thermophilic conditions. The highest organic loading rates which could be achieved were 0.9 g VS/L·d in digestion of SB and 1.5 g VS/L·d for the co-digestion mixtures. In these cases, average methane yields of 300, 510, 587 and 426 ml/g VS were obtained from the digestion of SB, and the co-digestion of SB:M, SB:VC and SB:VC: MSW, respectively, with methane contents in the biogas of 60-85%. The highest average methane yield of 587 ml/g VS was found in co-digestion of SB:VC, which was in accordance with the value of 592 ml/g VS detected during the batch digestion of the same mixture. Moreover, batch assays with different substrates as well as 11 different mixtures of those were also set up to investigate the methane potential and the effect of second feeding. The results showed that the co-digestion of SB:VC, SB:VC:MSW and SB:M could provide high methane potentials, where the highest methane yields of 592, 522 and 521 ml/g VS, respectively were obtained. Moreover, increasing, similar or decreasing methane yields were determined from the second feeding depending on the substrates and substrate mixtures used. / Program: MSc in Resource Recovery - Sustainable Engineering