This dissertation determines theoretical targets for producing biogas. Calculations were based on the relationship between the mass of substrate used (assumed to be glucose) versus the amount and composition of gas produced. Methane, hydrogen and carbon dioxide were considered as gases produced by biogas processes. The calculations undertaken to determine the production rates and environmental targets of the biogas production system were based on mass and energy balances as well as the second law of thermodynamics. These were applied to determine the limits of performance of the process. These limits are important due to the fact that they cannot be exceeded even if we genetically engineer organisms or change the equipment design or operation. Combining the results enabled us to plot an attainable region that showed the achievable composition of the gas as well as the minimum work and energy requirements for biogas production. It shows that the process is hydrogen and enthalpy (heat) limited. Furthermore the results show that a maximum of 3 moles of methane per mole of glucose are produced sustainably which in turn produces a large heat load of 142 kJ/mol of glucose. / Physics / M. Sc. (Physics)

Because of the increasing trends in energy consumption and increased environmental awareness, greater focus has been placed on improvement and development of renewable energy sources. An already proven and accepted method is biogas production from anaerobic digestion at municipal wastewater treatment plants. In the waste water treatment process solid material and dissolved pollutants are separated from the water, forming a sludge. The sludge is separated from the process and stabilized during anaerobic digestion or aerobic aeration. Most often, mesophilic anaerobic digestion is used. Because of degradation by microorganisms, biogas with a high content of methane is formed during the digestion. To optimize the process different studies with co-digestion with sludge and other substrate have been made. It has been showed, in earlier research studies, that co-digestion with microalgae and sewage sludge results in a synergistic effect with increased biogas production. As the microalgae are microorganisms which use photosynthesis they contain stored energy from sun light. The stored energy will be available when the microalgae are digested in mesophilic conditions. In contrast to other biomass suitable for co-digestion microalgae have the advantage of being able to grow in waste water and reduce the pollutants in the water phase. Cultivation of microalgae will therefore not compete with the cultivation of food production and at the same time has the possibility to decrease the electricity- and heat consumption at the wastewater treatment plants. The aim of this study was to investigate how a possible synergetic effect between microalgae and sewage sludge effects the biogas production and the process stability. The microalgae was cultivated in municipal waste water from the WWTP in Umeå (Sweden) and the sludge was collected from the WWTP in Västerås (Sweden). The fermenters used was of the type DOLLY© and the active volume was 5 dm3. The temperature in the fermenters was kept at 37 °C and the study was divided into two periods. During the first period the hydraulic retention time was 15 days and the organic loading rate 2.4 g VS dm-3 d-1. During the second period the hydraulicretention time was kept at 10 days and the organic loading rate was 3.5 g VS dm-3 d-1. The result showed an increase with 54.6 % in methane production per reduced VS in the fermenter with co-digestion compared to the fermenter where only sludge was digested. Period one showed the highest increase. The result also showed a good process stability for both fermenters during the whole experiment. This study shows that there are reasons for continued investigations about co-digestion with microalgae and sewage sludge for an increased biogas production. / På grund av ökande el- och värmeförbrukning och ökat miljöengagemang har större fokus lagts på förbättring och utveckling av förnyelsebara källor för el- och värmeproduktion. En redan beprövad och accepterad metod för framställning av förnyelsebar energi är från biogasproduktion vid kommunala reningsverk. Vid rening av avloppsvatten avskiljs fasta partiklar och lösta föroreningar och bildar ett slam som separeras från vattnet. Slammet kan sedan stabiliseras anaerobt genom rötning eller aerobt genom luftning. En ofta använd metod vid konventionella reningsverk är mesofil anaerob rötning. Vid rötningen bryts material ner av mikroorganismer och genererar biogas som framförallt innehåller metan och koldioxid. För att optimera en sådan process och därmed kunna utvinna mer gas har det tidigare undersökts hur samrötning med olika material påverkar biogasproduktionen. Det har visat sig i forskningsförsök att samrötning med mikroalger och orötat blandslam ger en synergieffekt och mer biogas produceras. Mikroalgerna innehåller lagrad energi från solljus, då de är fotosyntesiserande organismer. Den lagrade energin har visat sig bli tillgänglig vid mesofil anaerob nedbrytning. Till skillnad från annan biomassa som undersökts för samrötning kan mikroalgerna odlas på avloppsreningsverken och fungera som en del av reningsprocessen då mikroalgerna tar upp näringsämnen ur vattnet de växer i. På det sättet undviks konkurrens om odlingsmark för livsmedel och så blir reningsprocessen på avloppsreningsverken mer el- och värmeeffektiv. Syftet med studien var att undersöka om eventuell synergieffekt mellan mikroalgerna och slammet påverkar biogasproduktionen och processtabiliteten vid mesofil anaerob rötning. Mikroalgerna som användes var odlade på mekaniskt renat spillvatten från Umeås reningsverk och slammet som användes hämtades ifrån Västerås reningsverk. Rötkamrarna som användes var av modellen DOLLY© med en aktiv volym på 5 dm3. Temperaturen i rötkamrarna hölls kring 37°C och studien var uppdelad i två perioder. Under period ett var den hydrauliska uppehållstiden 15 dygn och den organiska belastningen 2,4 g VS dm-3 d-1, medan period två hade en hydraulisk uppehållstid på 10 dygn och en organisk belastning på 3,5 g VS dm-3 d-1. Resultaten visade att metangasproduktionen per tillförd mängd organiskt material var lägre vid samrötning jämfört med rötning av enbart slam. Metangasproduktionen per reducerad mängd organiskt material ökade med upp till 54,6 % vid samrötningen jämfört med rötning av enbart slam. Period ett gav upphov till den största ökningen. Processen hölls stabil även vid inblandning av mikroalger, under både period ett och två. Studien visar att det finns ett underlag för fortsatta studier kring samrötning av mikroalger och slam för en ökad biogasproduktion.

This dissertation determines theoretical targets for producing biogas. Calculations were based on the relationship between the mass of substrate used (assumed to be glucose) versus the amount and composition of gas produced. Methane, hydrogen and carbon dioxide were considered as gases produced by biogas processes. The calculations undertaken to determine the production rates and environmental targets of the biogas production system were based on mass and energy balances as well as the second law of thermodynamics. These were applied to determine the limits of performance of the process. These limits are important due to the fact that they cannot be exceeded even if we genetically engineer organisms or change the equipment design or operation. Combining the results enabled us to plot an attainable region that showed the achievable composition of the gas as well as the minimum work and energy requirements for biogas production. It shows that the process is hydrogen and enthalpy (heat) limited. Furthermore the results show that a maximum of 3 moles of methane per mole of glucose are produced sustainably which in turn produces a large heat load of 142 kJ/mol of glucose. / Physics / M. Sc. (Physics)

Swedish state has been promoting alternative renewable fuels like biogas to reduce the dependency on fossil fuels and to curb related greenhouse gas emissions. Owing to many policies like subsidies and tax exemptions for using biogas, the country has seen a surge in demand for biogas. Meanwhile, the increase in production of biogas in Sweden has been modest in recent years, though many studies have estimated substantially higher potentials from many sources. Agricultural feedstock/biomass is one among these sources where production and use of biogas could address many challenges faced by farmers like agricultural waste management, soil nutrient management, methane emissions from manure etc. while closing the nutrient cycle and contributing to sustainability.This work is an investigation on how to stimulate the growth of biogas production based on agricultural feedstock/biomass production in Sweden. Since policies give different results in different states/countries depending on the local preconditions, locally developed policies, national policies and EU policies should integrate well in all the policy sectors in that particular region to give the intended result. The current production capacity is about 2 TWh worth of biogas/year but the theoretical potential is estimated to be up to 15 TWh that has been claimed by many researches and literature works like in (Westlund, et al., 2019). Much of the potential has not been explored especially in the field of agriculture. It is asserted in many articles that the true potential of biogas production from Swedish agriculture is far greater than what is produced today. Yet, all the regulations, financial and other financial instruments failed to stimulate local biogas production in Sweden to attain its full theoretical potential. The results presented in this study show where these policies failed and what else apart from the policies could be improved in order promote biogas production.Farmers are hesitant to invest in biogas production because of the complexity and unpredictability of the existing policies. There has been significant negative impact from lack technological training of anaerobic digestion (AD) technology. This is also reflected as difficulties in finding trained and dedicated staff for biogas plant operations. Low profitability of biogas business exists ever since the production started and the financial aids are insufficient. Strict digestate regulations along with worsening substrate competition also creates problems. Permits to run the biogas plants are perceived to be expensive alongside increasing investment costs and taxes, affecting already low profitability. There is also a lack of infrastructure in terms of electricity/gas grid connectivity. Feed in tariffs for electricity produced from renewable sources are not bringing enough profitability to the business. Technological improvements are needed in terms of agricultural machinery that can use upgraded biogas as fuel and treatment of digestate to eliminate heavy metal content. Producers need more long term, sure market for their biogas. / Biogasmarknadsutredningen of BRC

The production of ethanol and other sustainable products including methane, limonene and pectin from citrus wastes (CWs) was studied in the present thesis. In the first part of the work, the CWs were hydrolyzed using enzymes – pectinase, cellulase and β-glucosidase – and the hydrolyzate was fermented using encapsulated yeasts in the presence of the inhibitor compound ‘limonene’. However, the application of encapsulated cells may be hampered by the high price of encapsulation, enzymes and the low stability of capsules’ membrane at high shear stresses. Therefore, a process based on dilute-acid hydrolysis of CWs was developed. The limonene of the CWs was effectively removed through flashing of the hydrolyzate into an expansion tank. The sugars present in the hydrolyzate were converted to ethanol using a flocculating yeast strain. Then ethanol was distilled and the stillage and the remaining solid materials of the hydrolyzed CWs were anaerobically digested to obtain methane. The soluble pectin content of hydrolyzate can be precipitated using the produced ethanol. One ton of CWs with 20% dry weight resulted in 39.64 l ethanol, 45 m3 methane, 8.9 l limonene, and 38.8 kg pectin. The feasibility of the process depends on the transportation cost and the capacity of CW. For example, the total cost of ethanol with a capacity of 100,000 tons CW/year was 0.91 USD/L, assuming 10 USD/ton handling and transportation cost of CW to the plant. Changing the plant capacity from 25,000 to 400,000 tons CW per year results in reducing ethanol costs from 2.55 to 0.46 USD/L in an economically feasible process. Since this process employs a flocculating yeast strain, the major concern in design of the bioreactor is the sedimentation of yeast flocs. The size of flocs is a function of sugar concentration, time and flow. A CFD model of bioreactor was developed to predict the sedimentation of flocs and the effect of flow on distribution of flocs. The CFD model predicted that the flocs sediment when they are larger than 180 micrometer. The developed CFD model can be used in design and scale-up of the bioreactor. For the plants with low CW capacity, a steam explosion process was employed to eliminate limonene and the treated CW was used in a digestion plant to produce methane. The required cost of this pretreatment was about 0.90 million dollars for 10,000 tons/year of CWs. / <p><strong>Sponsorship</strong>:</p><p>Sparbankstiftelsen Sjuhärad, Kommunalförbundet i Sjuhärad, Brämhults juice AB</p>

By 2018 at least 50 % of the Swedish food waste will be biologically treated. Stockholm Vatten are planning to quadruple the collection of food waste for biological treatment between 2015 and 2020. There are three different food waste collecting systems in Stockholm City; food waste bins, half open food disposer and sealed food disposer. The factor that affects the choice of collecting system are costs throughout the process, for example waste fees. Waste fees are seen as a powerful policy instrument to reduce unsorted waste, and should be designed to reduce overall waste, increase the sorting and reduce the environmental load. The purpose of the thesis is to design two decision models for collecting systems of food waste for biogas and digestate production. One model will be simple and be of support when deciding which system the kitchen should invest in, the other model will be designed to give an overview for each systems costs and processes from collection to production of biogas/digestate. The methodology was composed of a mixture of a qualitative and quantitative method, and a case study. The data collection was made by a literature study, mail contact, study tour and a map of the processes. The pre-treatment cost is 500kr/ton for food waste collected from bins, a cost that food waste does not accrue from disposers. The waste tariff is 57% lower for waste disposals, and they require 72% less transport when collected. The costs Stockholm Vatten have for transporting food waste is 75 % lower for waste disposals compared to food waste bins. If the waste tariff would reflect the costs more kitchens would choose waste disposals over food waste bins. Beside the differences in food waste bins and waste disposals, there are differences between types of waste disposals. Sealed food waste disposals require half of the transports compared to half open food waste disposals for the same biogas potential. When designing tariffs this should be taken in consideration. / Senast 2018 ska minst 50 % av det svenska matavfallet sorteras ut och behandlas biologiskt. Stockholm Vatten planerar att fyrdubbla insamlingen av matavfall till biologisk behandling under perioden 2015 till 2020. Det finns tre olika system för insamling av matavfall för storkök/restauranger i Stockholms Stad; kärlsystem, halvöppna kvarnsystem och slutna kvarnsystem. De faktorer som påverkar valet av insamlingssystem är kostnader genom processerna som exempelvis avfallstaxor. Avfallstaxorna ses som ett kraftfullt styrmedel för att minska uppkomsten av osorterat avfall och de ska utformas så de styr tydligare mot minskade avfallsmängder, ökad källsortering och minskad miljöbelastning. Syftet med studien är att utforma två beslutsmodeller för insamling av matavfall till biogas- och biogödselproduktion. Den ena modellen ska vara enkel och vara till stöd vid val av insamlingssystem, den andra modellen ska utformas för att ge en överblick för respektive systems kostnader och processer från insamling till produktion av biogas/biogödsel. Metodologin utgick ifrån en blandning av en kvalitativ och kvantitativ metod, samt fallstudie. Datainsamlingen utfördes genom litteraturstudie, mailkontakt, studiebesök och kartläggning av processer. Förbehandling har en kostnad på 500kr/ton matavfall, en kostnad matavfall från kvarnsystem inte kräver. Avfallstaxan är 57 % lägre för kvarnsystem i jämförelse med kärlsystem, dessutom krävs det 72 % mindre transporter med kvarnsystem. Stockholm Vattens kostnader för transport av matavfall från kärlsystem är 75 % högre än matavfall från kvarnsystem.  Ifall avfallstaxan skulle reflektera Stockholm Vattens kostnader skulle fler kök välja kvarnsystem över kärlsystem. Förutom att det finns en skillnad på kärl- och kvarnsystem finns det även skillnader mellan kvarnsystem. Slutna kvarnsystem kräver ca hälften så mycket transporter som halvöppna kvarnsystem för att få ut samma mängd biogaspotential. Vid utformning av taxor och priser bör detta finnas i åtanke.

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.

Small scale biogas plants (max digester volume 1000 m3) in Sweden produced in average 1.26 GWh per plant in 2014. Most of the biogas was used for combined heat and power production. The relatively cheap electricity in Sweden makes this a low profit business. If the biogas is upgraded to vehicle fuel its value will increase. However, upgrading biogas with conventional methods is costly, and for small scale biogas plants this cost cannot be justified. Development of alternative upgrading methods is an option to decrease the cost of upgrading and making small scale vehicle fuel production a reality. In this master thesis the upgrading method known as in-situ methane enrichment was investigated. This method involves desorption of carbon dioxide in the sludge using a desorption chamber separated from the digester. Air is blown through the sludge for desorption of carbon dioxide. Subsequently, the sludge is pumped back to the digester. The aim was to perform an energy mapping on the enrichment facility installed at the biogas plant (260 m3) at Sötåsens naturbruksgymnasium. In addition, the possibility to absorb ammonium-nitrogen in the off-gas from the process using a scrubber was also investigated in laboratory-scale. The results showed that the upgrading facility lost large quantities of heat during operation. During the coldest circumstances using an air flow of 260 m3/h through the sludge, the heat loss was 495 kWh/day. The corresponding efficiency of carbon dioxide removal was 7.6 kWh/m3 removed carbon dioxide. With proper insulation and heat recovery, the facility has the potential to decrease the heat demand to ca 139 kWh/day, giving an efficiency of 2.3 kWh/m3 removed carbon dioxide. The electric efficiency was 1 kWh/m3 removedcarbon dioxide. The laboratory test of ammonium-nitrogen absorption indicated that the plant has a potential to absorb 59 – 275 kg nitrogen/year by installing a scrubber with a volume of 122 l. The economic benefits are small, but other values such as reduced ammonia pollution or heat recovery solutions using a scrubber should be considered. / Biogas 2020

In den Themenbereichen Klimawandel, Klimaschutz und Erneuerbare Energien wurden in den letzten Jahren zunehmend neue Bewertungsmethoden in der geowissenschaftlichen und umweltwissenschaftlichen Forschung eingesetzt. Mit Blick auf die Biogasnutzung kann festgestellt werden, dass diese aus Umwelt- und Klimaschutzgründen sehr wichtig ist, da die Vergärung von Biomasse mit der nachfolgenden indirekten Erzeugung von Strom und Wärme über Blockheizkraftwerke, bzw. der direkten Nutzung des Biogases als Feuerungsgas bzw. als Treibstoff , einen besonderen Beitrag zum Klimaschutz leistet. In Deutschland ist die Biogasnutzung heute einer der wichtigsten Erneuerbaren Energieträger geworden. In China hat die Biogasnutzung zudem ein riesiges Entwicklungspotenzial. Der Autor versucht, im interdisziplinären Themenkreis „Umwelt- und Klimaschutz“ ein Bewertungsmodell für die Biogasnutzung zu entwickeln, um die tatsächlichen und potentiellen umwelt- und klimaschutzrelevanten Auswirkungen der Biogasnutzung zu bewerten. Um das Bewertungsmodell für die Biogasnutzung nach Umwelt- und Klimaschutzaspekten möglichst umfassend zu entwickeln, ist die Verzahnung der interdisziplinären umweltwissenschaftlichen, geowissenschaftlichen, rechtlichen, sowie lokal-, national- und internationalen politischen sowie technischen Faktoren mit ihren umweltbezogenen und klimabezogenen Auswirkungen von höchster Bedeutung. Das in der vorliegenden Arbeit entwickelte Bewertungsmodell erhebt den Anspruch, für den praktischen Einsatz vor Ort tauglich zu sein. Hierzu wurden umwelt- und klimaschutzrechtliche, sowie nationale und internationale politische Anforderungen zur Kategorisierung und Bewertung herangezogen und damit die Durchführbarkeit gewährleistet. Der Lösungsweg zur Bewertung nach Umwelt- und Klimaschutzaspekten führt zum Einen über die Umwelt- und Klimaschutzbilanzierung und zum Anderen über eine Umweltrisikobewertung sowie eine umweltbezogene Standortbewertung. Anhand der praktischen Arbeit und der Analyse von insgesamt 23 Biogasprojekten aus Deutschland und China, konnten bestimmte Charakteristika der Biogasnutzung ermittelt werden. Für die Ermittlung der Bewertungskriterien des Bewertungsmodells wurden insgesamt 3 Themenbereiche (Teil I: Substratversorgung; Teil II: Biogasanlagenbau; Teil III: Biogasverwertung) der Biogasnutzung unterschieden. Jene wurden hinsichtlich der technischen, rechtlichen und politischen Kriterien nach negativen Umwelt- und Klimaschutzauswirkungen über die verschiedenen Belastungspfade der Umweltmedien (Boden, Wasser und Luft) untersucht. Ziel dieser Studie war es auch, durch die Anwendung des Bewertungsmodells auf je drei deutsche und chinesische Fallbeispiele, die ausgereiften deutschen Erfahrungen, die deutsche Technologie und das Know-How der Biogasnutzung auf deren Übertragbarkeit auf die chinesischen Verhältnisse zu prüfen.

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