A utilização de inóculos líquidos na produção de Shiitake (Lentinula edodes (Berk.) Pegler) é uma tecnologia promissora para a industrialização do cultivo em sistema axênico, uma vez que permite a inoculação do micélio de forma rápida e bem distribuída, reduzindo riscos de contaminação e o período de incubação dos substratos. Neste trabalho, o cultivo submerso para a produção de micélio de Shiitake foi avaliado em um biorreator airlift de circulação externa, idealizado e projetado no grupo, utilizando o meio de cultura Mushroom Complete Medium adicionado de micronutrientes, nas condições de operação: taxas de aeração: 0.16, 0.20, e 0.24 vvm e tamanhos de inóculo (i.s.): 1.0 g.L-1 e 2.0 g.L-1. Na melhor condição de operação (0.16 vvm e 1.0 g.L-1 i.s.), um modelo matemático foi desenvolvido usando o software EMSO para descrever a cinética da cultura em ajuste aos dados experimentais. Foram atingidos 15,47 g.L-1 de biomassa total, após 10 dias de cultivo, 0,516 d-1 de taxa máxima de crescimento específico, fatores de rendimento Yx/s 1,06 g.g-1, YP/X 0,485 (g.L-1).g-1, YP/S 0,140 (g.L-1).g-1 e produtividade PX 0,061 (g.L-1).h-1. A predição do modelo demonstrou ser um parâmetro confiável para estudos de aumento de escala já que descreveu bons resultados preditivos para biomassa em relação aos produtos do metabolismo (CO2 e síntese de H+ pela acidificação do meio) e ao consumo de nutrientes (O2 e glicose). A seleção e a avaliação de linhagens no cultivo também são fatores a serem considerados para obtenção de boas produtividades e, deste modo, o desempenho produtivo de cinco linhagens de Shiitake foi avaliado em cultivo axênico, utilizando um planejamento composto central (CCD) para avaliar as variáveis independentes: tempo de incubação I(t), e percentual de farelo de trigo em relação a serragem Eucalypitus saligna (representada pela relação carbono/nitrogênio (RC/N)), tendo a eficiência biológica (BE) e o peso unitário dos cogumelos como resultados de destino . Os substratos utilizados tiveram sua composição físico-química determinada e as taxas de suplementação do substrato foram otimizadas, não só para o rendimento em cultivo, mas também para o crescimento vegetativo do micélio. Os melhores resultados de BE em todas as linhagens foram obtidos em cultivos com RC/N 57,62/1, com indução dos primórdios em 130 dias de I(t). Os cogumelos colhidos nesta condição de produção tiveram sua composição centesimal determinada. Atividades enzimáticas amilolíticas e celulolíticas, β-glicosidase e proteases específicas foram realizadas em ensaios de colonização do substrato. Três linhagens foram selecionadas para o isolamento de esporos e hibridização intraespecífica. As linhagens híbridas foram comparadas com as parentais em termos de rendimento e síntese das enzimas extracelulares. Os resultados deste trabalho demonstraram que a linhagem cultivada tem um efeito considerável sobre o rendimento, sobre o peso unitário e sobre a síntese de enzimas extracelulares produzidas pelo fungo, tanto pelas linhagens híbridas, como pelas parentais. / The use of liquid inoculant production of Shiitake (Lentinula edodes (Berk.) Pegler) is a promising technology for the industrialization farming of this fungus in axenic system because it allows the mycelium inoculation in a quick and well distributed way, thus reducing the risks of contamination and the incubation time of cultures. In this work, the submerged cultivation for the production of Shiitake mycelium was evaluated in an airlift bioreactor of external circulation, conceived and designed in the group, using the culture medium Mushroom Complete Medium added of micronutrients, under the operating conditions: rates of aeration: 0.16, 0.20, and 0.24 vvm and inoculum sizes (i.s.): 1.0 g. L-1 and 2.0 g. L-1. Under the best operating condition (0.16 vvm and 1.0 g L-1 i.s.), a mathematical model was developed using the EMSO software to describe the kinetics of culture fittnes to experimental data. It was possible to obtain 15.47 g L-1 of total biomass, after 10 days of cultivation, a maximum specific growth rate of 0.516 d-1, yields of Yx/s 1,06 g.g-1, YP/X 0,485 (g.L-1).g-1, YP/S 0,140 (g.L-1).g-1 and PX (productivity) 0.061 (g.L-1).h-1. The prediction of the model has proven to be a reliable parameter for studies for scaling up because it was predictive for biomass considering the products of metabolism (CO2 and H+ synthesis by acidification of the medium) and nutrient consumption (O2 and glucose). The selection and evaluation of strains in cultivation are also factors to be considered to obtain good productivity and, therefore, the productive performance of five strains of Shiitake cultivated under axenic system, was carried out using a central composition design (CCD) to evaluate the independent variables: incubation time I(t), and percentage of wheat bran in relation to sawdust of Eucalypitus saligna (represented by the carbon/nitrogen ratio (RC/N)), and having the biological efficiency (BE) and the unit weight of the mushrooms as target results. The best results for BE for all the strains were obtained in cultures with RC/N 57.62/1, with primordia induced at 130 days of I(t). The substrates used had their physico-chemical composition determined and the rates of substrate supplementation have been optimized, not only for the cultivation yields, but also for vegetative growth of the mycelium. The mushrooms harvested in this condition of production had their centesimal composition determined. Amilolytic, cellulolytic, β-glucosidase and specific proteases activities were performed in tests of colonization of the substrate. Three strains were selected for the isolation of spores and intraspecific hybridization was carried out. Hybrid strains were compared with the parental strains in terms of yields and synthesis of extracellular enzymes. The results of this study showed that strain has a considerable effect on both the yield and the unit weight of mushrooms.

ABSTRACT Photobioreactor Design for Improved Energy Efficiency of Microalgae Production Alexander Burns The objective of this research was to investigate a new photobioreactor (PBR) design for microalgae production that retains the typical advantages of existing tubular PBRs while reducing power consumption by providing simultaneous culture circulation and gas exchange with airlift alone and no centrifugal recirculating pump. Traditional tubular PBR designs feature a compressed air supply and a centrifugal pump for culture circulation and gas exchange. Circulation and gas exchange in a closed-system PBR is necessary to keep the algae suspended and to provide sufficient mass transfer (mainly for the exchange of oxygen and carbon dioxide). In a traditional tubular PBR sparged air keeps the culture well mixed and strips out excess dissolved oxygen in an airlift-column unit, while the centrifugal pump circulates the culture in the tubular stage and decreases the amount of air bubbles traveling into this stage; where most of the photosynthesis occurs. The PBR design proposed herein does away with the usual centrifugal pump. The air blower performs both gas exchange in the airlift columns and system-wide circulation. This builds on a previous tubular PBR design that provides circulation and gas exchange by airlift alone, which was patented by Cathcart in 2011. However, the Cathcart patent does not provide data on mixing, gas exchange, energy consumption, flow regime or biomass productivity. The new design described here builds on the Cathcart design, but includes several unique design features, such as larger diffuser columns which provide airlift-induced flow for a series of vertical PBR tubes. To perform a power consumption v analysis, a pilot-scale prototype of the new PBR design was built and operated. The prototype PBR consisted of two airlift columns attached to 9 m of vertical serpentine tubing connected to the top and bottom by standard 90-degree PVC elbows in a U-bend fashion to each column to make a total working volume of 235 L. The airlift columns were about 1.5 m tall and 30.5 cm ID, while the serpentine tubes were about 0.9 m tall and 7.6 cm ID to make a total of five vertical tubes for every airlift column. Data collected for this prototype design suggest an average overall areal productivity (OAP) of 111 g m-2 d-1 (g biomass m-2 total land area with empty space day-1), an average illuminated surface productivity (ISP) of 14.3 g m-2 d-1 (g biomass m-2 reactor photo-stage day-1), an average volumetric productivity (VP) of 0.55 g L-1 d-1 (g biomass L-1 reactor working volume day-1), a specific power input in the range of 330 to 360 W m-3 (W power needed for culture circulation and gas exchange m-3 reactor working volume) and a specific biomass productivity (SBP) in the range of 17.6 to 19.1 mg kJ-1 (mg biomass kJ-1 energy needed for culture circulation and gas exchange) with Chlorella vulgaris as the model algae. The biomass productivity per energy input (SBP) of the new PBR design appears to be higher than that of similar designs currently described in the literature. Elimination of the centrifugal pump in a tubular PBR design is a concept worth further study for potential energy savings.

No description available.

External loop airlift reactors are widely used for biochemical applications such as syngas fermentation and wastewater treatment. To further understand the inherent gas-liquid flow physics within the reactors, computational modeling and simulations of hydrodynamics for air-water external loop airlift reactors were investigated. The gas-liquid flow dynamics in a bubble column were simulated using a FORTRAN code developed by Los Alamos National Laboratory, CFDLib, which employs an Eulerian-Eulerian ensemble averaged method. A two-dimensional Cartesian coordinate system was used to conduct an extensive grid resolution study; it was found that grid cells smaller than the bubble diameter produced unstable solutions. Next, closure models for drag force and turbulent viscosity were investigated for a simple bubble column geometry. The effects of using a bubble pressure model and two drag coefficient models, the White model and the Schiller-Naumann model, were investigated. The bubble pressure model performed best for homogeneous (low velocity) flows and the Schiller-Naumann model was best for all flow regimes. Based on the studies for bubble column flows, an external loop airlift reactor was simulated using both two- and three-dimensional coordinates and results for gas holdup and riser velocity agreed better with experimental data for the 3D simulations. It was concluded that when performing 2D and 3D simulations, care must be taken when specifying the effective bubble diameter size, especially at high flow rates. Population balance models (PBM) for bubble break-up and coalescence were implemented into CFDLib, validated with experiments, and simulated for the external loop airlift reactor at high inlet superficial gas velocities. The PBM predictions for multiple bubble sizes were comparable with the single bubble size simulations; however, the PBM simulations better predicted the formation of the gas bubble in the downcomer. The 3D PBM simulations also gave better predictions for the average bubble diameter size in the riser. It was concluded that a two-dimensional domain is adequate for gas-liquid flow simulations of a simple bubble column geometry, whereas three-dimensional simulations are required for the complex airlift reactor geometry. To conclude, a two-fluid Eulerian-Eulerian model coupled with a PBM is needed for quantitative as well as physical predictions of gas-liquid external loop airlift reactor flows at high inlet superficial gas velocities. / Ph. D.

<p>U okviru doktorske disertacije izvedena su eksperimentalna istraživanja osnovnih hidrodinamičkih i maseno-prenosnih karakteristika airlift reaktora sa spoljnom recirkulacijom sa ugrađenom vi&scaron;ekanalnom cevnom membranom u silaznu cev (ALSRM). ALSRM je radio na dva načina rada: bez mehurova u silaznoj cevi (način rada A) i sa mehurovima u silaznoj cevi (način rada B) u zavisnosti od nivoa tečnosti u gasnom separatoru. Ispitivani su uticaji prividne brzine gasa, povr&scaron;inskih osobina tečne faze, tipa distributora gasa i prisustva mehurova gasa u silaznoj cevi na sadržaj gasa, brzinu tečnosti u silaznoj cevi i zapreminski koeficijent prenosa mase u tečnoj fazi u ALSRM. Rezultati su poređeni sa vrednostima dobijenim u istom reaktoru ali bez membrane (ALSR). Sadržaj gasa u uzlaznoj i silaznoj cevi određivan je pomoću piezometarskih cevi merenjem hidrostatičkog pritiska na dnu i vrhu uzlazne i silazne cevi. Brzina tečnosti merena je pomoću konduktometrijskih elektroda dok je zapreminski koeficijent prenosa mase dobijen primenom dinamičke metode merenjem promene koncentracije kiseonika u vremenu optičkom elektrodom. Eksperimentalni rezultati pokazuju da sadržaj gasa, brzina tečnosti i zapreminski koeficijent prenosa mase zavise od prividne brzine gasa, vrste alkohola i tipa distributora gasa kod oba reaktora. Vi&scaron;ekanalna cevna membrana u silaznoj cevi uzrokovala je povećanje ukupnog koeficijenta trenja za 90% i time dovela do smanjenja brzine tečnosti u silaznoj cevi do 50%. Smanjena brzina tečnosti u silaznoj cevi povećala je sadržaj gasa do 16%. Predložene neuronske mreže i empirijske korelacije odlično predviđaju vrednosti za sadržaj gasa, brzinu tečnosti i zapreminski koeficijent prenosa mase.</p> / <p>An objective of this study was to investigate the hydrodynamics and the gas-liquid mass transfer coefficient of an external-loop airlift membrane reactor (ELAMR). The ELAMR was operated in two modes: without (mode A), and with bubbles in the downcomer (mode B), depending on the liquid level in the gas separator. The influence of superficial gas velocity, gas distributor&rsquo;s geometry and various diluted alcohol solutions on hydrodynamics and gas-liquid mass transfer coefficient of the ELAMR was studied. Results are commented with respect to the external loop airlift reactor of the same geometry but without membrane in the downcomer (ELAR). The gas holdup values in the riser and the downcomer were obtained by measuring the pressures at the bottom and the top of the riser and downcomer using piezometric tubes. The liquid velocity in the downcomer was determined by the tracer response method by two conductivity probes in the downcomer. The volumetric mass transfer coefficient was obtained by using the dynamic oxygenation method by dissolved oxygen probe. According to experimental results gas holdup, liquid velocity and gas-liquid mass transfer coefficient depend on superficial gas velocity, type of alcohol solution and gas distributor for both reactors. Due to the presence of the multichannel membrane in the downcomer, the overall hydrodynamic resistance increased up to 90%, the liquid velocity in the downcomer decreased up to 50%, while the gas holdup in the riser of the ELAMR increased maximally by 16%. The values of the gas holdup, the liquid velocity and the gas-liquid mass transfer coefficient predicted by the application of empirical power law correlations and feed forward back propagation neural network (ANN) are in very good agreement with experimental values.</p>

Made available in DSpace on 2016-06-02T19:56:54Z (GMT). No. of bitstreams: 1 5928.pdf: 1538103 bytes, checksum: aa35e421fd67417964fb69c2b0a31753 (MD5) Previous issue date: 2014-02-28 / Agência Nacional de Petróleo / The performance of pneumatic bioreactors is highly related to their geometric characteristics, such as the bottom clearance, riser to downcomer cross sectional area ratio, liquid height and the gas-liquid separator design. Although new geometries have been proposed, it is still necessary deeper studies to obtain more adequate reactor projects for bioprocess applications. This study evaluated the influence of the gas-liquid separator design on the hydrodynamics and oxygen transfer of 10-L concentric-tube airlift bioreactors, using Newtonian and non- Newtonian fluids and in order to define the better set of geometric characteristics. To reach this aim, the gas-liquid separator openness angle (&#945;) varied from 30° to 90° and the volume fraction of fluid present on the gas-liquid separator section (FVL,GLS) varied from 0.10 to 0.30. The results indicated that for both fluids (Newtonian and non-Newtonian), the overall volumetric oxygen transfer coefficient (kLa) increased with the increase in &#945; and a decrease in FVL,GS. Meanwhile, this gas-liquid separator geometry caused low global gas hold-up (&#949;G), suggesting the reduction of mean bubble diameter (dB) for this condition. Operating with the non-Newtonian fluid at 5.0 vvm, the best gas-liquid separator geometry (&#945;=90°; FV L,GLS=0,10) exhibited kLa and &#949;G of 0,017 s-1 and 0,11, respectively. Moreover, this set of geometric characteristics lead to a gas-liquid flow with intermediate values for the drag coefficient (CD), suggesting moderate shear conditions. For the best geometry, the average shear rate varied from 1500 to 2400 s-1, in a similar range when compared to other airlift bioreactors. These results indicate the feasibility to use this bioreactor geometry in applications with shear-sensitive microorganisms. / O desempenho de biorreatores pneumáticos depende fortemente das suas características geométricas, como o vão livre na base, a razão entre as áreas de escoamento, a altura de líquido e o design da região de mistura. Embora diferentes geometrias tenham sido propostas na literatura, ainda há necessidade de estudos mais aprofundados, com o intuito de se obter projetos de biorreatores mais adequados aos bioprocessos. O presente estudo avaliou a influência da geometria da região de mistura na hidrodinâmica e transferência de oxigênio em biorreatores airlift de cilindros concêntricos de 10 L, empregando-se fluidos Newtonianos e não- Newtonianos, a fim de se definir o melhor conjunto de características geométricas. Para isso, variou-se o ângulo da região de mistura (&#945;) (ângulo entre a lateral da região de mistura e o eixo horizontal) de 30° a 90° e a fração volumétrica de líquido na região de mistura (FVL,RM) (razão entre o volume de líquido contido apenas na região de mistura e o volume de líquido total do biorreator) de 0,10 a 0,30. Os resultados mostraram que para ambos fluidos (Newtoniano e não-Newtoniano), o coeficiente volumétrico de transferência de oxigênio (kLa) aumentou com o incremento em &#945; e a diminuição de FVL,RM. Entretanto, esta configuração de geometria da região de mistura proporcionou baixa retenção gasosa (&#949;G), indicando baixos valores de diâmetro das bolhas (dB) nesta condição. Empregando-se a melhor geometria da região de mistura (&#945;=90°; FV L,RM=0,10), para o fluido não- Newtoniano, na condição de 5,0 vvm, obteve-se valores de kLa e &#949;G de 0,017 s-1 e 0,11, respectivamente. Além disso, verificou-se que esta combinação de parâmetros geométricos conduziu a um escoamento gás-líquido com valores intermediários de coeficiente de arrasto (CD), sugerindo condições amenas de cisalhamento. Através da estimativa da velocidade de cisalhamento média ( m &#61543;& ) para a melhor geometria em termos de transferência de oxigênio, observou-se uma variação entre 1500 e 2400 s-1, sendo estes valores da mesma ordem de grandeza quando comparados a outros biorreatores airlift. Esses resultados reforçam a viabilidade de utilização desta geometria em aplicações com microrganismos sensíveis ao cisalhamento.

With greenhouse gas emissions (of which CO2 is the major component) being a major environmental concern, mitigation of those emissions is becoming increasingly imperative. The ability to use a fast growing, photosynthetic organism like microalgae that can survive primarily on nutrients such as sunlight and air (with increased CO2 levels) makes it a desirable agent for CO2 sequestration. The primary goal of this project is the engineering of the sequestration of CO2 using the cultivation of the microalgae species <i>Chlorella vulgaris</i>. Secondary goals of the project are the exploration and development of valuable by-products of the cultivation and the determination of whether utilizing microalgae to capture CO2 could be integrated economically into an industrial facility.<p> The batch growth kinetics of the photosynthetic algal species <i>C. vulgaris</i> were investigated using a well-mixed stirred bioreactor. The growth rate was found to increase as the dissolved CO2 increased to 150 mg/L (10% CO2 by volume in the gas), but fell dramatically at higher concentrations. Increasing the radiant flux also increased growth rate. With a radiant flux of 32.3 mW falling directly on the 500 mL culture media, the growth rate reached up to 3.6 mg of cells/L-h. Both pH variation (5.5 - 7.0) and mass transfer rate of CO2 (KLa between 6 h-1 and 17 h-1) had little effect on growth rate.<p> The operation of continuously stirred tank bioreactors (CSTBs) at minimum cost is a major concern for operators. In this work, a CSTB design strategy is presented where impeller stirring speed and aeration rate are optimized to meet the oxygen demand of growing cells, simultaneously minimizing the capital and operating cost. The effect of microbial species, ions in the culture medium, impeller style, as well as changing CSTB size and biomass input density on the optimum operating conditions, is examined. A study of the effects of various parameters on the CSTB design is shown.<p> Using the kinetic data collected in the batch growth study, a novel external loop airlift photobioreactor (ELAPB) was designed and tested. A model was developed for <i>C. vulgaris</i> growth in the ELAPB that incorporated growth behaviour, light attenuation, mass transfer, and fluid dynamics. The model predicts biomass accumulation, light penetration, and transient CO2 concentrations, and compares predictions to experimental data for radiant fluxes of 0.075 1.15 W/m2 and 0 20% CO2 enrichment of feed air, with a 10% average error. The effect of radiant flux and CO2 concentration is presented with discussion of radial and vertical profiles along the column. For a fed-batch culture at a biomass density of 170 mg/L, the penetration of the radiant flux was found to decrease by 50% within the first 1 cm, and 75% at 2 cm. Theoretical optimum growth conditions are determined to be 0.30 W/m2 and 6% CO2 enrichment of inlet feed air.<p> The algal culture was observed to be a workable electron acceptor in a cathodic half cell. A net potential difference of 70 mV was achieved between the growing <i>C. vulgaris</i> culture acting as a cathode and a 0.02 M potassium ferrocyanide anodic half cell. Surge current and power levels of 1.0 µA/mg of cell dry weight and 2.7 mW/m2 of cathode surface area were measured between these two half cells. The recently developed photosynthetic cathode was also coupled to a fermentative anode to produce a completely microbial fuel cell. Loading effects and the effect of changing culture conditions on fuel cell operation are reported. The maximum power output measured was 0.95 mW/ m2 at 90 V and 5000 ohms. A significant increase in this output is achieved with the addition of supplemental glucose to the anodic half cell and the enrichment of the feed air bubbled into the cathodic half cell with 10% CO2.<p> Two economic feasibility studies were performed on the integration of ELAPBs into an industrial facility. These integration studies operated the ELAPBs continuously as biocathodes in coupled microbial fuel cells (MFCs) that capture CO2 from an existing 130 million L/yr bioethanol plant, while generating electrical power and yielding oil for biodiesel to provide operational revenue to offset costs. The anodes for the coupled MFCs are the existing yeast batch fermentors, and the CO2 to be sequestered comes from the existing bioethanol production. Two different design schemes were evaluated, in both cases the maximum profit was achieved with the maximum number of tall columns operated in parallel. The first design evaluated a batch bioethanol facility with off-site oil processing, and the economic feasibility is demonstrated by the positive Net Present Worth achieved over the 20 year life of the plant, at a 10% rate of return on investment. The second design, for a continuous bioethanol operation, processes both oil and algae biomass on-site, but the economics of this second process are only positive (Internal Rate of Return 9.93%.) if the government provides financial assistance in the form of generous carbon credits (a speculative $100 per tonne of CO2 not yet attained) and a 25% capital equipment grant.

With greenhouse gas emissions (of which CO2 is the major component) being a major environmental concern, mitigation of those emissions is becoming increasingly imperative. The ability to use a fast growing, photosynthetic organism like microalgae that can survive primarily on nutrients such as sunlight and air (with increased CO2 levels) makes it a desirable agent for CO2 sequestration. The primary goal of this project is the engineering of the sequestration of CO2 using the cultivation of the microalgae species <i>Chlorella vulgaris</i>. Secondary goals of the project are the exploration and development of valuable by-products of the cultivation and the determination of whether utilizing microalgae to capture CO2 could be integrated economically into an industrial facility.<p> The batch growth kinetics of the photosynthetic algal species <i>C. vulgaris</i> were investigated using a well-mixed stirred bioreactor. The growth rate was found to increase as the dissolved CO2 increased to 150 mg/L (10% CO2 by volume in the gas), but fell dramatically at higher concentrations. Increasing the radiant flux also increased growth rate. With a radiant flux of 32.3 mW falling directly on the 500 mL culture media, the growth rate reached up to 3.6 mg of cells/L-h. Both pH variation (5.5 - 7.0) and mass transfer rate of CO2 (KLa between 6 h-1 and 17 h-1) had little effect on growth rate.<p> The operation of continuously stirred tank bioreactors (CSTBs) at minimum cost is a major concern for operators. In this work, a CSTB design strategy is presented where impeller stirring speed and aeration rate are optimized to meet the oxygen demand of growing cells, simultaneously minimizing the capital and operating cost. The effect of microbial species, ions in the culture medium, impeller style, as well as changing CSTB size and biomass input density on the optimum operating conditions, is examined. A study of the effects of various parameters on the CSTB design is shown.<p> Using the kinetic data collected in the batch growth study, a novel external loop airlift photobioreactor (ELAPB) was designed and tested. A model was developed for <i>C. vulgaris</i> growth in the ELAPB that incorporated growth behaviour, light attenuation, mass transfer, and fluid dynamics. The model predicts biomass accumulation, light penetration, and transient CO2 concentrations, and compares predictions to experimental data for radiant fluxes of 0.075 1.15 W/m2 and 0 20% CO2 enrichment of feed air, with a 10% average error. The effect of radiant flux and CO2 concentration is presented with discussion of radial and vertical profiles along the column. For a fed-batch culture at a biomass density of 170 mg/L, the penetration of the radiant flux was found to decrease by 50% within the first 1 cm, and 75% at 2 cm. Theoretical optimum growth conditions are determined to be 0.30 W/m2 and 6% CO2 enrichment of inlet feed air.<p> The algal culture was observed to be a workable electron acceptor in a cathodic half cell. A net potential difference of 70 mV was achieved between the growing <i>C. vulgaris</i> culture acting as a cathode and a 0.02 M potassium ferrocyanide anodic half cell. Surge current and power levels of 1.0 µA/mg of cell dry weight and 2.7 mW/m2 of cathode surface area were measured between these two half cells. The recently developed photosynthetic cathode was also coupled to a fermentative anode to produce a completely microbial fuel cell. Loading effects and the effect of changing culture conditions on fuel cell operation are reported. The maximum power output measured was 0.95 mW/ m2 at 90 V and 5000 ohms. A significant increase in this output is achieved with the addition of supplemental glucose to the anodic half cell and the enrichment of the feed air bubbled into the cathodic half cell with 10% CO2.<p> Two economic feasibility studies were performed on the integration of ELAPBs into an industrial facility. These integration studies operated the ELAPBs continuously as biocathodes in coupled microbial fuel cells (MFCs) that capture CO2 from an existing 130 million L/yr bioethanol plant, while generating electrical power and yielding oil for biodiesel to provide operational revenue to offset costs. The anodes for the coupled MFCs are the existing yeast batch fermentors, and the CO2 to be sequestered comes from the existing bioethanol production. Two different design schemes were evaluated, in both cases the maximum profit was achieved with the maximum number of tall columns operated in parallel. The first design evaluated a batch bioethanol facility with off-site oil processing, and the economic feasibility is demonstrated by the positive Net Present Worth achieved over the 20 year life of the plant, at a 10% rate of return on investment. The second design, for a continuous bioethanol operation, processes both oil and algae biomass on-site, but the economics of this second process are only positive (Internal Rate of Return 9.93%.) if the government provides financial assistance in the form of generous carbon credits (a speculative $100 per tonne of CO2 not yet attained) and a 25% capital equipment grant.

This thesis examined the biological treatment of gas streams containing benzene, toluene, ethylbenzene and o-xylene (BTEX) using solid-liquid two-phase partitioning bioscrubbers (SL-TPPBs). SL-TPPBs consist of a cell containing aqueous phase and a polymeric solid phase that sequesters poorly water soluble and/or toxic substrates, mitigating substrate toxicity in the aqueous phase and improving the gas mass transfer during treatment of VOC contaminated gases. An initial investigation of oxygen transport determined that the polymers in a stirred-tank SL-TPPB enhance gas-liquid mass transfer. In addition, a study on biodegradation kinetics of BTEX by a bacterial consortium identified and quantified substrate interactions such as inhibition, enhancement and cometabolism. The stirred-tank SL-TPPB was then experimentally investigated for treatment of BTEX gas streams during steady-state and dynamic step-change operation to determine performance of the system relative to other biotreatment methods. A mathematical model was developed to predict system performance, which included the microbial kinetic model structure and parameters estimated during kinetic and oxygen mass transfer studies. As a less energy intensive alternative, an airlift SL-TPPB was operated and characterized. The airlift SL-TPPB was compared to an airlift liquid-liquid TPPB (silicone oil as sequestering phase) and a single phase airlift over dynamic step-change loadings, which showed that the airlift SL-TPPB outperformed the single phase airlift by >30% and had similar performance to the liquid-liquid airlift. However, the airlift SL-TPPB performance was lower relative to the stirred-tank SL-TPPB by >15%. Steady-state operation of the airlift SL-TPPB identified a range of operating conditions that provided maximum performance and conditions that were not oxygen limited. This prompted a study of oxygen mass transfer and hydrodynamics in the airlift system, which identified that the addition of polymers to an airlift does not cause physical enhancement of the gas-liquid mass transfer coefficient, but improves aqueous phase mixing and enhances overall oxygen transfer rate. A tanks-in-series mathematical model was formulated to predict performance of the airlift SL-TPPB, wherein the number of tanks-in-series to describe mixing in the airlift was obtained from a residence time distribution analysis of the airlift system completed during the hydrodynamic investigation. This thesis contributes a low-energy solution for the effective treatment of gases contaminated with BTEX. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2009-08-18 16:16:22.598

Neste trabalho é proposto o desenvolvimento de um processo para a biofixação do dióxido de carbono através do uso de microalgas. Para o cultivo desses microrganismos foram utilizados fotobiorreatores do tipo airlift. Nos cultivos foram avaliadas espécies de microalgas (Chlorella sp. e Chlorella minutissima), influência da intensidade luminosa (2.200 a 24.500 lx), concentração salina (28 a 40 g.L-1) e temperatura (25 °C a 35 °C) sobre a concentração de biomassa, velocidade específica de crescimento, produtividade de biomassa, biofixação de CO2, conteúdo lipídico e carotenoides totais. Também foi realizada a identificação dos carotenoides. A microalga escolhida para os testes em fotobiorreatores foi a C. minutissima. A intensidade luminosa que apresentou os melhores resultados foi a de 17.000 lx. A temperatura mostrou possuir influência significativa na concentração de biomassa, na velocidade específica de crescimento e na biofixação de carbono, mas a concentração salina influenciou apenas a velocidade específica de crescimento. A temperatura de 25 °C apresentou as maiores produtividade de biomassa (0,094 g.L-1.d-1) e concentração de biomassa (0,43 g.L-1), independente da concentração salina, e as maiores velocidade específica de crescimento (0,81 d-1) e biofixação de CO2 (12 gCO2.m-3.h-1), na concentração salina de 37 g.L-1. O conteúdo lipídico médio das microalgas foi de 13,2 % e os carotenoides totais apresentaram teor de 0,25 % do peso seco das microalgas em todas as condições de concentração salina e temperatura testadas. Foi possível identificar a produção dos carotenoides luteína, zeaxantina e β-caroteno. / The present study proposes the development of a process for carbon dioxide biofixation through the use of microalgae. Flat-plate airlift photobioreactors were used. Microalgaes species (Chlorella sp. and Chlorella minutissima) and the influence of light intensity (2,200 to 24,000 lx), salt concentration (28 to 40 g.L-1) and temperature (25 to 35 °C) over biomass concentration, specific growth rate, biomass productivity, CO2 biofixation rate, lipid content and total carotenoids content were evaluated. The identification of the carotenoids was performed. C. minutissima showed the best performance in shaker and was chosen for the tests in photobioreactor. The light intensity of 17,000 lx presented the best results. The temperature showed to have significant influence over biomass concentration, specific growth rate and CO2 biofixation rate, but the salt concentration only affected the specific growth rate. The temperature of 25 °C allowed the highest biomass productivity (0.094 g.L-1.d-1) and biomass concentration (0.43 g.L-1), independent of salt concentration, and the highest specific growth rate (0.81 d-1) and CO2 biofixation rate (12 gCO2.m-3.h-1) at the salt concentration of 37 g.L-1. The average lipid content of the microalgae was 13.2 % and the total carotenoids content were about 0.25 % of the cell dry weight at all temperatures and salt concentrations tested. It was possible to identify the production of the carotenoids lutein, zeaxanthin and β-carotene.