In present day society there is an artificial dichotomy between wastes and resources that is perhaps best summed up by the Western Sydney Waste Board slogan 'there is no such thing as waste � only resources in the wrong place and at the wrong time'. Waste management was originally driven by managing the health consequences of wrong time/place materials. This has changed and the significant driver is now the sustainable utilisation of resources, that is, trying to optimally recover as resources (right time/place) those materials that present as wastes requiring management. However, it is not acceptable to justify a resource recovery option purely on the basis that it is diverting material away from landfill. Preferences are emerging for recovery activities that maximise the resource value of a material according to techno-economic, environmental and socio-political criteria; collectively known as the criteria of sustainability. The people and organisations articulating these preferences include owners/operators of resource recovery centres, proponents of alternative waste management technologies, waste planners and managers at both a state and local government level and environmental NGOs representing community interests, in addition to the generators of waste at a domestic, commercial and industrial, and construction and demolition level. It is therefore important to be able to answer the question of 'what is the optimal or most sustainable resource recovery option for materials presenting as waste to landfill in the Greater Sydney Region?' The point of departure for this thesis is twofold. Firstly, that optimal resource recovery options (also known as alternative waste management technologies) can be identified by understanding the context and system drivers and constraints within the system of waste generation and utilisation, by modelling the system using industrial ecology (specifically Materials Flux Analysis) and by using the technology assessment framework developed by the NSW Alternative Waste Management Technologies and Practices Inquiry to evaluate the available options. Secondly, that should the assessment framework from the NSW Inquiry prove to be unsuitable as a framework for evaluation, then an improved and refined assessment framework can be constructed in order to identify optimal resource recovery options and that this process can be successfully demonstrated using wood waste as a case study. The context of waste as an issue has shifted from local government control (pre-1970s) to state government control through the Department of Environment and Conservation. This transition followed experiments with organisations such as the NSW Waste Boards and Resource NSW, in addition to state targets such as a 60% reduction of waste to landfill by the year 2000. In addition to this backdrop of change from a government administrative perspective, there are also a suite of often conflicting drivers and constraints influencing the process of resource recovery. For example, sustainable development is a public policy driver for the integration of environmental and societal concerns, but can also constrain new innovation if competing 'status quo' utilisation options are not subject to the same scrutiny. Similarly, legislation acts as a constraint to resource recovery options by establishing license conditions, prohibiting some energy recovery options and setting recovery criteria; however legislation also acts as a driver for resource recovery options that generate renewable electricity or act to reduce greenhouse gas emissions. Other drivers and constraints include social, technical and economic issues and concerns in addition to environmental impacts such as emissions to air, land and water. Industrial ecology is a model for viewing system components as part of a dependent and interrelated greater whole. Within the context of Industrial Ecology, waste is a by-product of manufacture available as a beneficial input into other processes. Using Materials Flux Analysis as a tool to build a model of waste generation and utilisation, elements within the system are presented as a series of stocks (sources), technology interventions (transformation flows) and sinks (markets). The stocks or sources of materials for resource recovery are categorised as Municipal Solid (MSW), Commercial and Industrial (C&I) or Construction and Demolition (C&D) wastes. Approximately seven million tonnes of waste is generated in the Greater Sydney Region (nearly two and a half million tonnes of materials recovered for recycling and four and a half million tonnes of materials disposed of to landfill). The purpose of technology intervention is to transform the material into a product that is suited to the end market (sink). Markets are grouped according to reuse (same function and form), direct recycling (same supply chain), indirect recycling (different supply chain) and energy recovery (either as process heat, electricity or co-generation, a combination of the two). Landfill is also a potential sink for materials and in this sense can be thought of as a negative value market. The Alternative Waste Management Technologies and Practices Inquiry provided an assessment framework for resource recovery technologies. Each technology was measured and compared against 16 evaluation criteria, resulting in a score out of one hundred. Material sorting scored the highest (81.5), incineration the lowest (50.8) with most of the biological technologies performing �well� (64.6 � 71.7) and with the landfill technologies performing 'moderately well' (60.4 - 61.4). The positive features of the Inquiry included the overview of alternative resource recovery technologies, waste generation and other issues pertinent to decision making and resource recovery. The negatives of the Inquiry arise from the inadequacies of the assessment framework, which lacked technology options, system boundary definition and requisite evaluation criteria in addition to inconsistencies in scoring approaches. By undertaking a sensitivity analysis on the Inquiry�s results, it is shown that rank order reversal results from the allocation of weightings. The improved and refined assessment framework, constructed to overcome identified inadequacies of the Inquiry�s approach, focussed on clearly identifying the problem to be addressed and the primary decision maker involved in the process; ensuring that appropriate options for evaluation were included; defining the system boundary for the assessment; selecting necessary evaluation criteria; adopting a more sophisticated system for scoring; and using a sensitivity analysis to validate the results of the resource recovery option evaluation. Wood waste was used as a case study for this second assessment methodology. Wood waste refers to the end-of-life products, failed products, offcuts, shavings and sawdust from all timber products. Approximately 350,000 tonnes of wood waste are disposed of to landfill each year. This comprises untreated timber (hard wood and soft wood), engineered timber products (particleboard, medium density fibreboard and plywood) and treated timber (predominately copper chrome arsenic). Eight wood resource recovery options are selected for evaluation within the Greater Sydney Region with a different approach to scoring that has the advantage of 'scaling up' the best performers within each attribute (highest score) while 'scaling down' the worst performers (no score). Under this evaluation, an on-site purpose built energy facility is the most preferred option with particleboard manufacture the least preferred option. A sensitivity analysis of the results reveals that the scores of each technology option are sensitive to the weightings of the decision maker. When the change in rankings is examined, it is identified that two eight wood recovery options undergo a large rank reversal. A critique of the results of the wood evaluation reveals five major flaws. Firstly the evaluation produces non-highest resource value results that are non-intuitive (and arguably misleading), for example the poor performance of reuse and particleboard against energy generation options. Secondly, the recording of a single summary score for each recovery option hides unacceptable performance levels in some criteria. For example, the top scorer of Primary Energy On-site hides the fact that such an option is likely to have no political desirability (likely public opposition to 'incineration' within the Sydney air-shed), calling into question its ability to be implemented as a solution. Thirdly there is a reliance on judgement for the scoring of options and weighting of preferences, calling into doubt the accuracy of scores. Fourthly, the rankings of recovery options by the assessment framework are sensitive to the allocation of weightings. Finally and most importantly, the refined evaluation approach suffers from the 'discrete option syndrome', the scoring of each recovery option in isolation with no ability to look at integrated systems with joint recovery options. This is pinpointed as a fundamental flaw in the process of both the Inquiry and the wood evaluation. This leads to the conclusion that the founding assertions of this thesis were false. That is to say that the assessment framework developed by the NSW Alternative Waste Management Technologies and Practices Inquiry is not suitable for use in evaluating resource recovery options. Furthermore a refined assessment framework based on this approach is also unable to identify optimal resource recovery options as demonstrated using wood waste as a case study. The results of this research points to the overall conclusion that any discrete option evaluation and assessment for resource recovery technologies that results in a single summary score for each option will be fundamentally flawed, providing no value in determining optimal resource recovery solutions for the Greater Sydney Region. A systems approach is suggested as an alternative method for the evaluation of optimal resource recovery, the starting point of which is to ask 'what is the highest resource value of the components in the material stream under consideration and how could a network of infrastructure be designed in order to allow materials to flow to their highest resource value use?' A feature of such an integrated approach is a focus on the materials composition of recovered resources, as opposed to recovery technologies, resulting in a 'fit for purpose' as opposed to a 'forced fit' style of resource recovery. It is recommended that further research and public policy efforts be made in logistics planning across the Greater Sydney Region (as opposed to a regional or local government area) in order to create network opportunities for integrated flows of materials to move toward their highest resource value.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves ).

Anaerobic digestion (AD) is a biotechnology that employs natural microbial metabolism under oxygen-free conditions to stabilize organic waste. AD has been shown to be the most environmentally sustainable technology for treating the organic fraction of municipal solid waste (OFMSW), as it allows for the recovery of energy and nutrients from the waste. AD of OFMSW also saves landfill space and reduces leachate generation and fugitive methane emissions from landfills. High-solids AD (HS-AD) technologies (those designed to process feedstocks with >15% total solids content) have been shown to yield additional benefits when compared with liquid AD (L-AD) for treating OFMSW, including reduced parasitic energy demands, reactor volume requirements, water usage, and excess leachate generation. These factors paired with increasingly stringent environmentally-driven legislation have resulted in the steady development of HS-AD technologies in Europe since the 1990’s and the recent advancement of HS-AD in the United States. However, HS-AD implementation in the US is hindered by the low cost of landfilling and a general lack of regulatory drivers encouraging organics separation and recycling. The goal of this research was to contribute to accelerating the implementation and improving the efficiency of HS-AD technologies. The specific objectives were to: (i) assess the state of the art of HS-AD in Europe and the US and investigate trends in development; (ii) conduct a case study assessment of the outlook for implementation of HS-AD in the state of Florida; and (iii) investigate the potential to enhance methane (CH4) yields in HS-AD of lignocellulosic wastes through bioaugmentation with pulp and paper mill anaerobic sludge. Information sources for the assessment of the state of HS-AD in Europe and the US included “grey” and published literature and discussions with consultants and technology vendors. In Europe as of 2014 there were 244 full-scale AD facilities for processing OFMSW with a total capacity of almost 8 million tons per year (TPY), approximately 89% of capacity was “stand-alone” (systems treating only OFMSW), 62% was HS-AD, and 70% installed since 2009 was HS-AD. In the US, as many as 181 AD facilities are now processing OFMSW with an approximate total capacity of 780,000 TPY. Only 24% of the total capacity is currently stand-alone HS-AD with the remaining capacity being stand-alone L-AD (28%) or L-AD codigestion (48%) at wastewater treatment plants or on-farm systems. Development trends in the US are mirroring those in the EU, however, with stand-alone capacity steadily increasing and HS-AD capacity increasing particularly rapidly relative to L-AD for OFMSW processing. The number of full-scale HS-AD facilities in the US has increased from one in 2011 to eight in 2015 and another 19 systems are expected to be operational by 2017. There are at least nine vendors of HS-AD technologies in the US, including four with facilities currently in operation and another four with projects in the planning, permitting, or construction phases. Landfill bans and taxation, mandated source-separation of OFMSW, and policies incentivizing recycling and renewable energy generation are critical factors driving the development and implementation of HS-AD. The case study of HS-AD implementation in Florida incorporated information from industry and data from the Florida Department of Environmental Protection. There is high demand for organics recycling in Florida, with numerous counties generating several hundred thousand TPY of OFMSW and lacking organics recycling infrastructure. HS-AD implementation could increase the statewide recycling rate by as much as 13% and contribute significantly to the reaching the state’s recycling goal of 75% by 2020. Furthermore, up to 7,000 and 3,500 TPY of bioavailable nitrogen and phosphorus, respectively, and up to 500 MW of energy could be recovered through HS-AD of OFMSW in the state. Based on current energy conversion efficiencies, 500 MW of energy translates to either 175 MW of electricity (approximately 660,000 metric tons of CO2 equivalents offsets per year) and 200 MW of heat or nearly 80 million diesel gallon equivalents of vehicle fuel. However, because of the low cost of both landfilling and energy in the state and the lack of markets for compost and renewable energy certificates, legislative action is needed to improve the economic feasibility of HS-AD. Accordingly, a number of policy recommendations were formulated, including banning disposal of OFMSW to landfills and mandating source-separation of OFMSW by all generation sources. Two phases of side-by-side bench-scale batch HS-AD experiments were carried out to investigate the potential to enhance CH4 yield from lignocellulosic waste in HS-AD through bioaugmentation with pulp and paper mill anaerobic sludge. In the first phase, the average CH4 yield from yard waste inoculated with pulp and paper sludge reached 100.2 ± 2.4 L CH4/kg VS, a 73% enhancement compared with the average CH4 yield achieved through inoculation with domestic wastewater anaerobic sludge (58.1 ± 1.2 L CH4/kg VS). In the second phase, CH4 yield from yard waste inoculated with digestate from digesters originally inoculated with pulp and paper sludge was 68% greater than the CH4 yield achieved through inoculation of yard waste with digestate from digesters originally inoculated with domestic wastewater sludge (36.5 ± 0.2 L CH4/kg VS versus 21.7 ± 0.4 L CH4/kg VS). The enhancement in CH4 yield achieved in this study is comparable to enhancements achieved through lignocellulosic pretreatment methods. However, this strategy incurs significantly less additional environmental and economic costs when compared with pretreatment, suggesting that it could serve as an alternative to pretreatment and improve the overall sustainability of HS-AD processes.

When we consider global sanitation from within the framework of sustainable development, we are both failing to meet the needs of the present and are jeopardizing the capacity of future generations to do so. The primary function of sanitation and waste treatment is the protection of public health, but it is urgent that we also consider the long-term sustainability of sanitation and waste treatment systems. Our choice of sanitation and waste treatment systems is intimately connected to the greatest equity and sustainability challenges of our time, and we need something better than the Porcelain Dream (i.e. flush toilets, sewerage, and centralized conventional wastewater treatment). This thesis explores the design of sustainable sanitation systems from three different but complementary perspectives: 1. In a material flow analysis (MFA), I evaluate the positive impact of ecological sanitation (or the reuse of nutrients in excreta for agriculture) as an intervention to mitigate nitrogen pollution and improve stewardship of the global nitrogen cycle. I find that ecological sanitation can substitute 51% of nitrogenous fertilizer use, reduce discharge of nitrogen to waterways by 71%, decrease nitrous oxide (N2O) emissions by 34%, and improve the circularity of the agricultural-sanitation nitrogen cycle by 22%. 2. Through environmental engineering research, I derive fundamental drying characteristics of fresh faeces to support the development of ecological and sustainable sanitation. Based on this characterization, I propose the use of the Guggenheim, Anderson, and de Boer (GAB) model for predicting the relationship between water activity (aw) and equilibrium moisture content, calculating the heat of sorption, and estimating the corresponding energy requirements for drying of fresh faeces. Given an anticipated range of initial moisture contents of 63 to 86%, I estimate an energy requirement of 0.05 to 0.4 kJ/mol to inactivate pathogens in fresh faeces. 3. Via an evaluation of the composting toilet project at the University of Victoria (UVic), I explore factors critical to promoting a paradigm shift from the conventional to more ecological and sustainable systems. I identify the following as factors that facilitated implementation in the Exploration and Adoption/Preparation phases: supportive and self-reinforcing research and outcomes, favorable adopter characteristics, and the technology’s beneficial features. The overall objective of the research is to communicate that the design of sustainable sanitation systems is urgent, with implications both locally and globally, and to provide information to support a shift towards more sustainable sanitation systems. / Graduate / 2020-12-11

The recovery processes of critical metals from multiple sources have turned more and more attention due to the increasing demand and consumption of them in modern industry. Many metals are used as significant components in manufacturing of a variety of products and equipment, playing significant roles in the economic security and national security; those metals involve rare earth elements (REEs), precious metals which include gold, silver, and platinum group metals (PGMs), and other valuable metals such as lithium, uranium, nickel, et al. The traditional approach to obtaining the above metals is by hardrock mining of natural ores via chemical and physical processes. However, this method of mining and refining metals from minerals is usually energy-consuming, costly, and environmental-destructive. Thus, various approaches to extracting or recycling target metals from the seawater or the solution of secondary resources as an alternative to traditional hardrock mining have been developed, and thereinto, using functional porous adsorbents to selectively capture specific metal ions from the aqueous resources has attracted increasing attention due to its outstanding merits such as high efficiency, energy-saving process, low cost, and reduced environmental impacts

Research about resource recovery from complex waste streams is getting an increased scientific attention since valuable resources can be produced by sustainable biological means. In anaerobic degradation processes, resources such as volatile fatty acids (VFAs) and biogas are highly coveted. One of the key parameters affecting the yield of resources is the hydrolytic efficiency in the waste stream by hydrolytic bacteria. The aim of this study was to examine how bioaugmentation can be implemented as a strategy to enhance hydrolysis in complex waste streams. In pursuit of this aim, three selected species of hydrolytic bacteria, Bacteroides thetaiotaomicron, Bacteroides amylophilus and Bacteroides ruminicola were inoculated both in pure culture combinations and bioaugmented with granular sludge as mixed culture in reactors. The studied waste stream was food waste mixed with primary sludge collected from Henriksdals wastewater treatment plant at Stockholm, Sweden.  The highest hydrolytic efficiency (90%) was reached by the pure culture fermented reactor inoculated with Bacteroides thetaiotaomicron and Bacteroides ruminicola. This efficiency was measured at day 10 after reactor set-up. Among the bioaugmented reactors, highest hydrolytic activity (66%) was achieved by the reactor inoculated with Bacteroides thetaiotaomicron and it was measured at day 10. The increase in hydrolytic efficiency for bioaugmented reactors was slower compared to pure culture fermented reactors and the most probable reason to that is due to competition amongst introduced species and pre-existing mixed culture in granular seed sludge. / Mer uppmärksamhet riktas till forskning kring resursåtervinning från komplexa avfallsströmmar eftersom värdefulla resurser kan produceras genom mer hållbara biologiska tillvägagångssätt. I anaeroba nedbrytningsprocesser är produkter såsom flyktiga fettsyror (VFAs) och biogas mycket eftertraktade. En av huvudparametrarna som påverkar utbytet av återvunna resurser är den hydrolytiska effektiviteten i avfallsströmmen av hydrolytiska bakterier. Syftet med studien var att undersöka hur bioaugmentering kan implementeras som strategi för att förstärka hydrolys i komplexa avfallsströmmar. Därav utfördes fermentering med tre valda hydrolytiska bakterier, Bacteroides thetaiotaomicron, Bacteroides amylophilus och Bacteroides ruminicola både i renkultur och bioaugmenterat med granulärt slam som mixad kultur i reaktorer. Avfallsströmmen som studerades var matavfall mixat med primärt slam hämtat från Henriksdals vattenreningsverk i Stockholm, Sverige.  Högsta hydrolytiska effektivitet (90%) uppnåddes för reaktorn inokulerat med Bacteroides thetaiotaomicron och Bacteroides ruminicola i renkultur. Denna effektivitet uppmättes dag 10 efter reaktorerna sattes upp. För de bioaugmenterade reaktorerna så uppnåddes högsta hydrolytiska effektivitet (66%) dag 10 av reaktorn inokulerat med Bacteroides thetaiotaomicron. Ökningen i hydrolytisk effektivitet var långsammare för de bioaugmenterade reaktorerna jämfört med reaktorerna med renkultur. Den mest sannolika förklaringen till det är tävling om näringsämnen och vitaminer mellan introducerade bakterier och de bakterier som redan existerar i det granulära slammet.

While the terms reduce, reuse, and recycle are common concepts in minimizing resource waste, most people do not think twice about energy as a resource or the large amounts of wasted energy in wastewater treatment and industrial processes. Recovery of wasted energy or reducing the net energy consumption of such processes would save resources and reduce energy costs. This research investigated emerging energy systems for handling wastewater (bioelectrochemical systems) and waste heat (ion exchange membrane systems) to elucidate and quantify thermodynamic and kinetic phenomena in biological and electrochemical reactions. Bioelectrochemical systems utilize exoelectrogenic microorganisms for wastewater treatment energy recovery in the form of electricity or biogas. The substrate utilization and electron transfer by exoelectrogens to the bioanode have not been clearly explained and thus there are no commonly accepted models for bioanode performance. A comprehensive model for bioanode operation was proposed including equilibrium, kinetics, and microbiological characteristics. The utilization and preference of different organic substrates were also assessed with electrochemical techniques and it was found that linear sweep voltammetry and exchange current are good indicators of whether a substrate is directly or indirectly utilized by exoelectrogenic microorganisms. This research also investigated ion exchange membrane systems for energy recovery from waste-grade heat, such as that wasted in the steel refinery and power industries, using concentration gradients of ammonium bicarbonate solutions. Estimation of the junction potential (amount of concentration gradient energy) has significant technical difficulties for highly concentrated ammonium bicarbonate solutions (e.g., unknowns in equilibrium speciation and activity coefficient determination). A straightforward estimation method was proposed and found to be able to reliably determine the junction potential across an ion exchange membrane based on conductivity measurement, simplifying the model for junction potential determination. / Thesis / Doctor of Philosophy (PhD)

Recovering valuable resources from wastewater will transform wastewater management from a treatment focused to sustainability focused strategy, and creates the need for new technology development. An innovative treatment concept - osmotic bioelectrochemical system (OsBES), which is based on cooperation between bioelectrochemical systems (BES) and forward osmosis (FO), has been introduced and studied in the past few years. An OsBES can accomplish simultaneous treatment of wastewater and recovery of resources such as nutrient, energy, and water (NEW). The cooperation can be accomplished in either an internal (osmotic microbial fuel cells, OsMFC) or external (microbial electrolysis cell-forward osmosis system, MEC-FO) configuration. In OsMFC, higher current generation than regular microbial fuel cell (MFC) was observed, resulting from the lower resistance of FO membrane. The electricity generation in OsMFC could greatly inhibit the reverse salt flux. Besides, ammonium removal was successfully demonstrated in OsMFC, making OsMFCs a promising technology for "NEW recovery" (NEW: nutrient, energy and water). For the external configuration of OsBES, an MEC-FO system was developed. The MEC produced an ammonium bicarbonate draw solute via recovering ammonia from synthetic organic solution, which was then applied in the FO for extracting water from the MEC anode effluent. The system has been advanced with treating landfill leachate. A mathematical model developed for ammonia removal/recovery in BES quantitatively confirmed that the NH4+ ions serve as effective proton shuttles across cation exchange membrane (CEM). / Ph. D.

Efforts are made to change from 1st to 2nd generation bioethanol production, using lignocellulosics as raw materials rather than using raw materials that alternatively can be used as food sources. An issue with lignocellulosics is that a harsh pretreatment step is required in the process of converting them into fermentable sugars. In this step, inhibitory compounds such as furan aldehydes and carboxylic acids are formed, leading to suboptimal fermentation rates. Another issue is that lignocellulosics may contain a large portion of pentoses, which cannot be fermented simultaneously with glucose by Saccharomyces cerevisiae. In this thesis, high local cell density has been investigated as a means of overcoming these two issues. Encapsulation of yeast in semi-permeable alginate-chitosan capsules increased the tolerance towards furan aldehydes, but not towards carboxylic acids. The selective tolerance can be explained by differences in the concentration of compounds radially through the cell pellet inside the capsule. For inhibitors, gradients will only be formed if the compounds are readily convertible, like the furan aldehydes. Conversion of inhibitors by cells close to the membrane leads to decreased concentrations radially through the cell pellet. Thus, cells closer to the core experience subinhibitory levels of inhibitors and can ferment sugars. Carbohydrate gradients also give rise to nutrient limitations, which in turn trigger a stress response in the yeast, as was observed on mRNA and protein level. The stress response is believed to increase the robustness of the yeast and lead to improved tolerance towards additional stress. Glucose and xylose co-consumption by a recombinant strain, CEN.PK XXX, was also improved by encapsulation. Differences in affinity of the sugar transporters normally result in that glucose is taken up preferentially to xylose. However, when encapsulated, cells in different parts of the capsule experienced high and low glucose concentrations simultaneously. Xylose and glucose could thus be taken up concurrently. This improved the co-utilisation of the sugars by the system and led to 50% higher xylose consumption and 15% higher final ethanol titres. A protective effect by the capsule membrane itself could not be shown. Hence, the interest in flocculation was triggered, as a more convenient way to keep the cells together. To investigate whether flocculation increases the tolerance, like encapsulation, recombinant flocculating yeast strains were constructed and compared with the non-flocculating parental strain. Experiments showed that strong flocculation did not increase the tolerance towards carboxylic acids. However, the tolerance towards a spruce hydrolysate and especially against furfural was indeed increased. The results of this thesis show that high local cell density yeast cultures have the potential to aid against two of the major problems for 2nd generation bioethanol production: inhibitors and simultaneous hexose and pentose utilisation. / <p>Akademisk avhandling som för avläggande av teknologie doktorsexamen vid Chalmers tekniska högskola försvaras vid offentlig disputation den 19 februari 2014,klockan 13.30 i KA-salen, Kemigården 4, Göteborg.</p>

Lignocellulosic biomass is a potential feedstock for production of sugars, which can be fermented into ethanol. The work presented in this thesis proposes some solutions to overcome problems with suboptimal process performance due to elevated cultivation temperatures and inhibitors present during ethanol production from lignocellulosic materials. In particular, continuous processes operated at high dilution rates with high sugar utilisation are attractive for ethanol fermentation, as this can result in higher ethanol productivity. Both encapsulation and membrane bioreactors were studied and developed to achieve rapid fermentation at high yeast cell density. My studies showed that encapsulated yeast is more thermotolerant than suspended yeast. The encapsulated yeast could successfully ferment all glucose during five consecutive batches, 12 h each at 42 °C. In contrast, freely suspended yeast was inactivated already in the second or third batch. One problem with encapsulation is, however, the mechanical robustness of the capsule membrane. If the capsules are exposed to e.g. high shear forces, the capsule membrane may break. Therefore, a method was developed to produce more robust capsules by treating alginate-chitosan-alginate (ACA) capsules with 3-aminopropyltriethoxysilane (APTES) to get polysiloxane-ACA capsules. Of the ACA-capsules treated with 1.5% APTES, only 0–2% of the capsules broke, while 25% of the untreated capsules ruptured within 6 h in a shear test. In this thesis membrane bioreactors (MBR), using either a cross-flow or a submerged membrane, could successfully be applied to retain the yeast inside the reactor. The cross-flow membrane was operated at a dilution rate of 0.5 h-1 whereas the submerged membrane was tested at several dilution rates, from 0.2 up to 0.8 h-1. Cultivations at high cell densities demonstrated an efficient in situ detoxification of very high furfural levels of up to 17 g L-1 in the feed medium when using a MBR. The maximum yeast density achieved in the MBR was more than 200 g L-1. Additionally, ethanol fermentation of nondetoxified spruce hydrolysate was possible at a high feeding rate of 0.8 h-1 by applying a submerged membrane bioreactor, resulting in ethanol productivities of up to 8 g L-1 h-1. In conclusion, this study suggests methods for rapid continuous ethanol production even at stressful elevated cultivation temperatures or inhibitory conditions by using encapsulation or membrane bioreactors and high cell density cultivations. / <p>Akademisk avhandling som för avläggande av teknologie doktorsexamen vid Chalmers tekniska högskola försvaras vid offentlig disputation den 4 april 2014, klockan 9:30 i KE-salen, Kemigården 4, Göteborg.</p>