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Brazil is one of the largest economies in the Global South. Because of the country’s strong agribusiness and large population, it has a huge potential for biogas production that has yet to be realized. Biogas systems could potentially address a broad range of social, environmental, and economic issues, such as improving accessibility to clean energy sources in rural areas, alternative cooking fuel, and providing proper treatment of organic waste. Hence, biogas systems can play an important role in sustainability transitions by improving the environmental performance of energy generation, waste management systems, and food production. However, despite the availability of substrate for biogas production and the multiple benefits that biogas systems could bring, there is still a large implementation gap.   Biogas systems go beyond technical components and involve a multitude of stakeholders, infrastructure, knowledge, and formal and informal institutions. Therefore, the diffusion of biogas systems cannot be explained only by analyzing the technical components of biogas systems. Previous studies have explored the influences of societal contexts on technological diffusion, but these explored countries in the Global North. However, social, economic, and political aspects differ significantly between Global North and Global South countries.   This thesis aims to explain how societal contexts influence the diffusion of biogas systems in Brazil. The thesis distinguishes between societal contexts, delineating them as societal environments and socio-economic structures. Societal environments refer to the circumstances and aspects surrounding the diffusion process where alignment processes between new socio-technical systems and society happen across five environments: user, business, regulatory, cultural, and trans-local. Socio-economic structures refer to societal arrangements that shape social and economic aspects of society. The Varieties of Capitalism framework provides a tool for comparison of the socio-economic structures of different countries in the Global North and South. The thesis relies on case studies based on quantitative and qualitative data from documents (scientific articles, news articles, technical reports, research reports, official documents by governmental agencies, and policies) and interviews.    Societal contexts appear to be more unstable and fragmented compared to counterparts in the Global North, influencing the diffusion of biogas systems. Hierarchical structures in Brazil lead to power disparities between administrative levels (municipal, state, and federal levels), impacting policymaking and hindering local-level biogas system configurations. The thesis highlights socio-economic diversity among Brazilian states and how it influences where and which biogas system configurations are formed. This thesis emphasizes that studies on biogas systems’ potential should consider contextual aspects beyond substrate availability to comprehensively understand biogas systems diffusion in diverse settings. / Brasilien är en av de största ekonomierna i den globala södern. Givet landets starka jordbruksindustri och stora befolkning finns goda förutsättningar för storskalig biogasproduktion. Men det är en potential som ännu inte har exploaterats i någon större utsträckning. Biogassystem har potential att bidra till lösningen på flertalet sociala, miljömässiga och ekonomiska frågor, såsom att förbättra tillgången till rena energikällor på landsbygden, erbjuda alternativa bränslen för matlagning och att tillhandahålla lämplig behandling av organiskt avfall. Därmed kan biogassystem spela en viktig roll i en hållbar omställning genom att förbättra miljöprestandan för energiproduktion, avfallshantering och livsmedelsproduktion. Trots de många fördelarna som biogassystem medför finns alltså fortfarande en stor klyfta mellan potentialen och vad som är realiserat.   Biogassystem sträcker sig bortom tekniska komponenter och inkluderar även en mångfald av intressenter, infrastruktur, kunskap samt formella och informella institutioner. Därför kan spridningen av biogassystem inte förstås enbart genom att analysera tekniska komponenter i biogassystemet. Tidigare studier som har studerat hur sådana bredare samhällsfaktorer påverkar spridningen av teknologi har huvudsakligen undersökt länder i västvärlden (det globala norr). Men sociala, ekonomiska och politiska aspekter skiljer sig betydligt mellan länder i det globala norr och det globala söder.   Denna avhandling syftar därför till att förklara hur olika samhällsfaktorer påverkar spridningen av biogassystem i Brasilien. Avhandlingen skiljer mellan olika sorters samhällsfaktorer och delar in dem i samhälleliga miljöer och socioekonomiska strukturer. Samhälleliga miljöer avser de omständigheter och aspekter som omger spridningsprocessen där anpassningsprocesser mellan nya sociotekniska system och samhället sker över fem miljöer: användarmiljön, affärsmiljön, den reglerande miljön, den kulturella miljön och den translokala miljön. Socioekonomiska strukturer avser samhälleliga arrangemang som formar sociala och ekonomiska aspekter av samhället. För att jämföra socioekonomiska strukturer i olika länder i det globala norr och globala söder används även ramverket ”Varieties of Capitalsim” som beskriver olika former av kapitalism. Avhandlingen baseras på fallstudier och använder kvantitativa och kvalitativa data från dokument (vetenskapliga artiklar, nyhetsartiklar, tekniska rapporter, forskningsrapporter, officiella dokument från statliga organ och policys) samt intervjuer. Resultaten visar att de studerade samhällsfaktorerna i Brasilien verkar vara mer instabila och fragmenterade jämfört med motsvarigheter i det globala norr, vilket påverkar spridningen av biogassystem negativt. Hierarkiska strukturer i Brasilien leder till maktobalans mellan administrativa nivåer (kommunal, delstatlig och federal nivå), vilket påverkar politiskt beslutsfattande och hindrar utvecklingen av biogassystem på lokal nivå. Avhandlingen lyfter fram betydelsen av socioekonomisk mångfald bland Brasiliens delstater och hur dessa påverkar var och vilka biogassystem som utvecklas. Avhandlingen understryker att studier om biogassystems potential bör överväga kontextuella aspekter bortom tillgång på substrat för att bättre förstå spridningen av biogassystem i olika sammanhang. / <p><strong>Funding:</strong> the Biogas Solutions Research Center (BSRC)</p>

Facing the pressure of population growth and global warming, this dissertation provided an array of innovative carbon-efficient wastewater treatment technologies for resource recovery, process intensification, and anammox featured next generation biological nutrient removal (BNR) technologies. These technologies aim to supplant traditional carbon-intensive treatment processes with more sustainable alternatives. To this end, the dissertation first comprehensively reviewed what resources can be recovered from wastewater, and how these valuable resources can contribute to the carbon neutrality in water resource reclamation facilities (WRRFs) and help achieve sustainable society development. Then, the effect of mixed liquor recycle (MLR) configurations on the process intensification through continuous-flow aerobic granulation was explored in plug flow reactors. The results demonstrated that MLR configuration could hinder the sludge granulation, but the hindrance could be alleviated to some extent by its location change. In order to eliminate the energy consuming MLR, endogenous denitrification was taken advantage through a synergistic integration with partial nitrification, partial denitrification anammox (PdNA), and enhanced biological phosphorus removal (EBPR). This idea was tested in a pilot setup treating real primary effluent under highly variable influent conditions and low temperatures. The results showcased substantial carbon savings while meeting the stringent effluent requirements. To take a deeper dive into the PdNA performance and the underlying mechanisms, two parallel pilot-scale moving bed biofilm reactor (MBBR) treatment trains fed with methanol and glycerol, respectively, were operated in a local WRRF. Their efficacies in achieving stringent nutrient removal targets and carbon savings were compared. The impacts of operational conditions on the mechanisms and performance were elucidated. In the culmination of this dissertation, a sidestream process intensification and resource recovery technique, namely thermal hydrolysis pretreatment (THP) enhanced anaerobic digestion (AD), was experimented to compare the efficiencies between thermophilic and mesophilic AD when integrated with THP. To sum up, this dissertation not only advanced our understanding of carbon-efficient wastewater treatment processes but also laid the groundwork for their practical implementation, contributing to the global effort towards sustainability. / Doctor of Philosophy / Wastewater treatment consumes 3-4% of the energy produced in the U.S. and contributes to approximately 1.6% global greenhouse gas emissions. This dissertation aims to advance a series of carbon-efficient technologies specifically tailored for sustainable wastewater treatment. To this end, a variety of valuable resources that can be recovered or reused in wastewater treatment plants was firstly reviewed. Then, an advanced technology that can turn dispersed bacteria into bacteria aggregates was tested with real wastewater in a local wastewater treatment plant. Although these bacteria aggregates allow more wastewater to be treated with less small footprint, which was great, it was realized from this study that the formation of these bacteria aggregates was hindered by the nitrate water recycle which has been commonly practiced for using influent carbon for nitrogen removal. This nitrate water recycle consumed excessive energy for its high flow rate. To save this energy, a novel bioprocessing design was developed to eliminate the need for this nitrate water recycle by using carbon stored in bacterial cells. This new design also incorporated phosphorus recovery capacity and a low carbon nitrogen removal technique into one consolidated system to create an all-in-one solution to meet the stringent wastewater treatment requirement. This low carbon nitrogen removal technique harnessed a special group of bacteria that can use ammonia to reduce nitrite to nitrogen gas. Hence, only minor carbon source needs to be provided to reduce nitrate to nitrite for these bacteria to utilize. Two types of carbon sources, namely methanol and glycerol, were compared in a pilot-scale study to understand their efficiencies in generating nitrite. Results indicated that although both types of carbon sources can work, methanol is better suited for low strength wastewater treatment. These results provided an engineering basis for the full-scale application of the technology in the same wastewater treatment plant where the pilot study was performed. Besides liquid treatment, a carbon efficient solid treatment technology was also studied. The bottleneck constraining the rate of sewage sludge conversion to flammable menthane gas was identified, which provided engineering guidance for the design of the solid treatment process that can destroy more sewage sludge within smaller reactor spaces. In essence, this dissertation offers promising solutions for modern wastewater treatment plants to achieve low carbon wastewater treatment without compromising the treatment performance.

Yes / An Euler-Lagrange CFD model is applied to a full-scale, biogas-mixed anaerobic digester to improve mixing efficiency and improve overall performance. Two quantitative mixing criteria previously adopted in anaerobic digestion (viz., uniformity index and dead volume) are critically assessed for the first time. A novel qualitative method is introduced to clarify the output of the quantitative methods. The first-ever quantitative assessment of mixing quality in full-scale, biogas-mixed anaerobic digestion is then proposed, and a strategy to improve mixing, involving the combined use of concentric nozzle manifolds at the base of the digester, is evaluated. / University of Birmingham (UK) Postgraduate Teaching Assistantship award; University of Bradford (UK) Postdoctoral research assistant contract, who provided financial support