Development and optimization of microalgae cultivation systems: microalgal composition, photobioreactor design and characterization

Tese de doutoramento em Biological and Chemical EngineeringThis work aimed at the development and optimization of systems and techniques for microalgae cultivation, in order to make the process economically and environmentally sustainable. Three different strategies were adopted: i) maximize productivity through the optimization of culture conditions, ii) maximize productivity and decrease costs by the use of agro-industrial waste as cultivation medium; iii) development of a new, low cost and highly productive microalgae cultivation system. Carbon dioxide (CO2) is the most widely used carbon source for photoautotrophic growth of microalgae. The rate of CO2 fixation (RCO2) by Chlorella vulgaris was maximized by defining the values of CO2 concentration in air feed and aeration rate. The results revealed that the maximum RCO2 (2.22 g L-1 d-1) was obtained using 6.5% (v/v) CO2 and 0.5 vvm. Although biomass concentration and mass productivity were affected by growth conditions, no differences were obtained in the biochemical composition of cells. The optimization of specific productivity (starch and lipids for the production of bioethanol and biodiesel, respectively) was performed using strategies of nutrient limitation. Starch accumulation in C. vulgaris cells was evaluated under different initial concentrations of urea (nitrogen source) and FeNa-EDTA (iron source) in the medium. Based on the results, a two-stage process for obtaining culture cells with high concentrations of starch (> 40%) was proposed: a first stage of cultivation with initial urea and FeNa-EDTA concentrations of 1 and 0.08 g L-1, respectively, which aims at maximizing biomass productivity, followed by a second stage of cultivation in the absence of these nutrients to induce starch accumulation. The increase of lipid content in Parachlorella kessleri cells was induced using a culture medium dilution strategy. Photosynthetic carbon partitioning into starch and neutral lipid, as well as the influence of nutrient depletion and repletion on growth and pigment content in the green microalga P. kessleri were studied. The study revealed that P. kessleri used starch as a primary carbon and energy storage, but the stress caused by the decrease of nutrients concentration made the microalgae to shift the fixed carbon into reserve lipids as a secondary storage product. These findings indicate that nutritional limitation can be used in P. kessleri cultivation as a very effective and cheap strategy to increase lipid productivity, for biofuel production. Growth parameters and biochemical composition of the green microalga C. vulgaris cultivated under different mixotrophic conditions were determined and compared to those obtained from a photoautotrophic control culture. Supplementation of the inorganic culture medium with hydrolysed cheese whey powder solution, when compared photoautotrophic growth, led to a significant improvement in microalgal biomass production (from 0.10 ± 0.01 to 0.75 ± 0.01 g L d-1) and an increase in carbohydrate utilization when compared with the culture enriched with a mixture of pure glucose and galactose (from 80.5 and 49.5% of glucose and galactose utilization, respectively, to an utilization of 100% of these carbohydrates), possibly due to the presence of growth promoting nutrients in cheese whey. Mixotrophic cultivation of C. vulgaris using the main dairy industry by-product could be considered a feasible alternative to reduce the costs of microalgal biomass production, since it does not require the addition of expensive carbohydrates to the culture medium. A characterization of liquid and gas phases was performed, the mass transfer coefficient was determined, together with the light distribution profiles and flow patterns of three different photobioreactors (PBRs), namely bubble column (BC), split cylinder airlift photobioreactor (SCAPBR) 75 and SCAPBR 50. The effect of these parameters on biomass productivity was discussed. The developed SCAPBRs proved to be extremely suitable for microalgae cultivation. The design of photobioreactors (PBR), particularly the designed gas sparger, allowed meeting the needs of microalgae in terms of efficient mixing and good mass transfer coefficients (efficient supply and removal of CO2 and O2, respectively). SCAPBR 50 (at UGr = 0.0044 m s-1) showed, among the tested PBRs, the highest value of biomass productivity (0.75 g L-1 d-1). This result has been attributed to a higher efficiency of light distribution inside the PBR and to a regular and defined flow pattern, which allows exposing cells to regular light-dark periods, as demonstrated in the present workA realização deste trabalho visou o desenvolvimento e optimização de sistemas e técnicas de cultivo de microalgas de forma a tornar o processo económica e ambientalmente sustentável. Três estratégias distintas foram adoptadas: i) maximização da produtividade recorrendo à optimização das condições de cultivo; ii) maximização da produtividade e diminuição de custos recorrendo à utilização resíduos agroindustriais como meio de cultivo; iii) desenvolvimento de um novo sistema de cultivo de baixo custo e elevada produtividade. O dióxido de carbono (CO2) é a fonte de carbono mais utilizada no crescimento fotoautotrófico de microalgas. A taxa de fixação de CO2 (RCO2) por parte da Chlorella vulgaris, foi optimizada através da definição dos valores de concentração de CO2 e taxa de arejamento. Os resultados obtidos revelaram que a RCO2 máxima (2,22 g L-1 d-1) foi observada utilizando 6,5 % CO2 e 0,5 vvm. Apesar da concentração de biomassa e produtividade mássica terem sido afectadas pelas condições de cultivo, não foram obtidas diferenças na composição bioquímica das células. A optimização da produtividade específica (amido e lípidos destinados à produção de bioetanol e biodiesel, respectivamente) foi efectuada recorrendo a estratégias de limitação nutricional. A acumulação de amido em células de C. vulgaris foi avaliada sob diferentes concentrações iniciais de ureia (fonte de azoto) e FeNa-EDTA (fonte de ferro) no meio de cultivo. Com base nos resultados obtidos, foi proposto um processo de cultivo para a obtenção de células com elevadas concentrações de amido (> 40%), composto por duas fases: uma primeira fase de cultivo com concentrações iniciais de ureia e FeNa-EDTA de 1,1 e 0,08 g L-1, respectivamente, que tem como objectivo maximizar a produtividade em biomassa; seguida por uma segunda etapa de cultivo sem a presença destes nutrientes, induzindo a acumulação de amido nas células. O aumento do teor de lípidos em células Parachlorella kessleri foi induzida utilizando como estratégia a diluição do meio de cultura. A partição do carbono fotossintético em amido e lípidos neutros, bem como a influência da depleção e repleção de nutrientes no crescimento e teor de pigmentos na microalga P. kessleri foi estudada. O estudo revelou que a P. kessleri utiliza amido como fonte primária de armazenamento de carbono e energia, mas o stress causado pela diminuição da concentração de nutrientes faz a microalga direcionar o seu metabolismo para a acumulação de lípidos, sendo estes reserva energética secundária. Estes resultados indicam que a limitação nutricional pode ser usada na P. kessleri cultivo como uma estratégia muito eficaz e barata para aumentar a produtividade de lípidos. Foram determinados os parâmetros de crescimento e composição bioquímica da microalga C. vulgaris, cultivada em diferentes condições de mixotrofia, e comparados com os obtidos no cultivo padrão, efectuado em condições fotoautotróficas. A suplementação do meio de crescimento com soro de queijo hidrolisado levou a um aumento muito significativo da produtividade em termos de biomassa quando comparado com o crescimento fotoautotrófico (de 0,10 ± 0,01 para 0,75 ± 0,01 g L d-1) e a um aumento da utilização dos hidratos de carbono presentes no meio quando comparado com uma cultura enriquecida apenas com glucose e galactose (de 80,5 e 49,5% de consumo de glucose e galactose, respectivamente, para 100% de utilização destes hidratos de carbono), possivelmente devido à presença de nutrientes do soro de queijo que promovem o crescimento. O cultivo mixotrófico de C. vulgaris recorrendo ao principal subproduto da indústria dos lacticínios, pode ser considerada como uma alternativa bastante promissora para a redução de custos da produção de microalgas. A caracterização das fases líquida e gasosa, bem como a determinação do coeficiente de transferência de massa, a determinação do perfil de distribuição da luz e do padrão de fluxo foi efectuada em três fotobioreactores diferentes (BC, SCAPBR 75 e 50). Os SCAPBRs desenvolvidos revelaram-se extremamente adequados para o cultivo de microalgas. O design do SCAPBR, particularmente o sistema de arejamento desenvolvido, permitiu colmatar na totalidade as necessidades da microalga em termos de coeficientes de massa de mistura eficientes (fornecimento eficiente e remoção de CO2 e O2, respectivamente). SCAPBR 50 (com UGr = 0,0044 m s-1) apresentou o valor mais elevado de produtividade (0,75 g L-1 d-1). Este resultado deveu-se a uma maior eficiência da distribuição de luz no interior da PBR e um padrão de fluxo regular e definido, o que permite expor as células a ciclos regulares de luz e sombra

Optimizing digital archiving: An artificial intelligence approach for OCR error correction

Project Work presented as the partial requirement for obtaining a Master's degree in Data Science and Advanced Analytics, specialization in Business AnalyticsThis thesis research scopes the knowledge gap for effective ways to address OCR errors and the importance to have training datasets adequated size and quality, to promote digital documents OCR recognition efficiency. The main goal is to examine the effects regarding the following dimensions of sourcing data: input size vs performance vs time efficiency, and to propose a new design that includes a machine translation model, to automate the errors correction caused by OCR scan. The study implemented various LSTM, with different thresholds, to recover errors generated by OCR systems. However, the results did not overcomed the performance of existing OCR systems, due to dataset size limitations, a step further was achieved. A relationship between performance and input size was established, providing meaningful insights for future digital archiving systems optimisation. This dissertation creates a new approach, to deal with OCR problems and implementation considerations, that can be further followed, to optimise digital archive systems efficiency and results

Business intelligence no suporte à decisão estratégica

Em pleno século XXI, com um mundo em constante mudança, as organizações procuram constantemente prever os seus acontecimentos futuros, por forma a que tomem decisões por vezes com algum grau de complexidade, de uma forma ágil e expedita, baseada na informação que geram e dispõem. Os sistemas de apoio à decisão têm tido uma importância fundamental no meio organizacional, desde a automatização de processos das atividades diárias, até apoiar os agentes decisores a formular as melhores diretrizes ao nível estratégico, tático ou operacional. Com o novo paradigma da indústria 4.0, é levada a cabo uma revolução nestes sistemas nas organizações, que hoje se denomina de Business Intelligence. Neste contexto, são criados sistemas avançados de recolha de dados e informação relevante para a tomada de decisão, combinando diversas ferramentas que irão permitir aumentar a inteligência organizacional, auxiliando a estruturar conhecimento fundamental para delinear e executar as melhores resoluções para problemas internos e externos. Os sistemas de Business Intelligence trazem consigo tecnologias associadas, nomeadamente Data Warehousing, Online Analytical Processing e Data Mining, que serão abordadas no presente projeto de dissertação. Presente este novo paradigma, foi projetado para uma empresa de desenvolvimento de produtos de software uma arquitetura de um modelo de Business Intelligence para avaliar determinados parâmetros financeiros. Partindo dos dados do ERP da empresa, foi projetado um processo de Data Mining usando o software RStudio, caracterizado por ser open source e oferecendo grandes possibilidades de exploração de recursos de BI. Procedeu-se à construção de uma ferramenta front-end para visualização da informação usando o RShiny, com possibilidade de inúmeras personalizações. Vai permitir em tempo real a monitorização dos indicadores financeiros e de gestão, permitindo também fazer projeções para o futuro, que vão servir de suporte à tomada de decisão dos agentes decisores. Os avanços obtidos até ao momento possibilitam confirmar a utilidade destas ferramentas, havendo margem para grandes progresso

Gestão de qualidade nos Serviços de Gestão Académica da Universidade de Aveiro

Mestrado em GestãoO objetivo deste trabalho é desenvolver um modelo que permita efetuar uma avaliação dos serviços administrativos prestados numa Instituição de Ensino Superior (IES), especificamente aos Serviços de Gestão Académica (SGA) da Universidade de Aveiro. Em face da literatura revista e com base no modelo concetual, foram propostas um conjunto de 5 hipóteses que se centram no facto de as dimensões de qualidade em serviços (ie: tangibilidade, confiança, capacidade de resposta, garantia e empatia) poderem afetar a satisfação geral com o serviço, quer por parte dos clientes externos (alunos e familiares) quer por parte dos clientes internos (pivots departamentais) quer ainda por parte dos funcionários dos SGA. Para além disso, procurou-se verificar se a satisfação demonstrada por estes três tipos de clientes é condicionada pelo facto de o serviço ser prestado numa altura de baixa ou elevada procura. Numa primeira fase, após a análise fatorial, foi efetuada uma regressão linear multivariada no sentido de validar as 5 hipóteses em situações de baixa e de elevada procura por parte dos clientes externos e funcionários dos SGA, tendo os clientes internos (pivots departamentais) apenas sido inquiridos num momento intermédio. Tendo estas hipóteses sido validadas, foi efetuada uma regressão linear múltipla que permitiu aferir a influência das 5 dimensões de qualidade na satisfação, quer em períodos de elevada procura, quer em períodos de baixa procura. Finalmente foi efetuada uma comparação sistemática da forma como o desempenho e a importância dos fatores é avaliada pelos clientes externos e pelos funcionários em períodos de baixa e elevada procura, sendo ainda feita uma análise para os pivots departamentais num momento intermédio. Em conclusão procurou-se identificar um conjunto de medidas que permitam gerir e melhorar o desempenho da organização e do serviço prestado.The objective of this work is to develop a model that performs an assessment of the administrative services of a Higher Education Institution (HEI), specifically to the Academic Administrative Services of the University of Aveiro. Given the literature reviewed and based on a conceptual model, it was proposed a set of five hypotheses that focus on the fact that the dimensions of quality in services (i.e.: tangibility, reliability, responsiveness, assurance and empathy) can affect the general satisfaction with the service, either by external customers (students and families) or internal clients (departmental pivots), or the employees of Administrative Services. Furthermore, it was evaluated if the satisfaction demonstrated by these three types of customer is conditioned by the fact that the service is provided at a time of low or high demand. After an initial factorial analysis, it was performed a multivariate linear regression in order to validate the 5 cases in situations of low and high demand from external customers and employees of Academic Administrative Services. After validating these hypotheses, a multiple linear regression was performed which allowed assessing the influence of the five dimensions of quality in periods of high or low demand. Finally, a systematic comparison of how the performance of the different factors and their importance is evaluated by external customers and the departmental pivots in periods of low and high demand was finally made. As a conclusion, and based on this data, this work tries to identify a set of measures to manage and improve the performance of the organization and of the services provided

Biosorption of Cr(VI) by an E. coli biofilm supported on GAC

The increasing concern with environmental pollution significantly motivates the investigation and development of safe remediation technologies. The retention of contaminants by a biofilm supported on granular activated carbon is one of the promising technologies. This study aims the investigation and development of an innovative process for the removal of chromium (VI) from wastewater. The effect of the initial concentration of metal was tested, the polysaccharide and polymeric net of the E.Coli biofilm were quantified and the application of this system to a real effluent was made. The industrial effluent was provided by tannery factories. The support used for the biofilm formation was granular activated carbon (GAC) from MERCK with an average particle size of 2.5 mm, characterised by N2 adsorption (77K) with an ASAP Micromeritics 2001 which indicated a Langmuir area of 1270 m2g-1 and an average pore diameter of 2 nm. The use of activated carbon as a support is justified by the fact that this material is a versatile adsorbent due to its high surface area, porous structure, high adsorption capacity and surface chemical nature. The role of the biofilm was evaluated considering that microorganisms are quite adequate for heavy metals biosorption due to their ability to sorb metal ions, suitability for natural environments and low cost. Minicolumns (internal diameter = 2 cm, ht = 30 cm) were used for open systems studies, partially filled with GAC (15 g). The metal solutions were passed in upflow through the column with a flow rate of 5 ml/min (residence time of 19 min). Samples (5 ml) were taken, centrifuged and analyzed for metals using atomic absorption spectrophotometry, AAS. The results showed uptake values of 0.19 mg/gbiosorbent, 3.60 mg/gbiosorbent and 4.61 mg/gbiosorbent, respectively for the initial concentration of 10, 50 and 100 mg/l. The quantification of polysaccharides and polymeric net reveled a value of 4.77 mg/gbiosorbent for the polysaccharides and 142 mg/gbiosorbent, for the polymeric net. The polyssacharide and polymeric net give importante informations about the capacity of biofilm formation by the microrganism. The studies made with the industrial effluent showed values of Cr uptake of 0.093 mg/gbiosorbent, for an initial concentration of 4.2 mg/l. The value obtained for the removal percentage with the most diluted solution used (10 mg/l) was of 18% (after 10 hours of experiment) and the value of removal percentage obtained with the industrial effluent was of 9%, for the same period of time. This can be explainded by the fact that another compounds present in the industrial effluent than Cr(VI) can compete for the same active sites

Light regime characterization in a photobioreactor for cultivation of microalgae with high starch content for bioethanol production

The slow development of microalgal biotechnology is due to the failure in the design of large-scale photobioreactors (PBR) where light energy is efficiently utilized. In this work, both the quality and the amount of light reaching a given point of the PBR were determined and correlated with cell density, light path length and PBR geometry. This was made for two different geometries for the downcomer of an airlift PBR using optical fiber technology that allows obtaining information about quantitative and qualitative aspects of light patterns. This is important since the ability of microalgae to use the energy of photons is different, depending on the wavelength of the radiation. The results show that the circular geometry allows a more efficient light penetration, especially in the locations with a higher radial coordinate (r) when compared to the plane geometry; these observations were confirmed by the occurrence of a higher fraction of illuminated volume of the PBR for this geometry. An equation is proposed to correlate the relative light intensity (RLI) with the penetration distance (Pd), for both geometries and different microalgae cell concentrations. It was shown that the attenuation of light intensity is dependent on its wavelength, cell concentration, geometry of PBR and the penetration distance of light

Utilization of dairy industry by-products as substrates to enhance the productivity of microalgae production systems

The mixotrophic growth of the microalgae Chlorella vulgaris was studied using diverse substrates, namely cheese whey (CW) which is a by-product from dairy industry, cheese whey hydrolysate (CWH), lactose and a glucose/galactose mixture. Growth parameters and biochemical profile of cells were monitored. Our results demonstrate that the use of CW and CWH as substrate for mixotrophic growth, stimulates the growth of Chlorella vulgaris, leading to the achievement of high biomass productivities. In terms of biochemical composition, the results indicate that mixotrophic growth influence the pigment content, but does not have a significant influence on lipid, starch and protein content, thus mixotrophy it is only responsible for a considerable increase in the productivity in terms of these constituents, but not for an increase of its content

Third generation biofuels from microalgae

Biofuel production from renewable sources is widely considered to be one of the most sustainable alternatives to petroleum sourced fuels and a viable means for environmental and economic sustainability. Microalgae are currently being promoted as an ideal third generation biofuel feedstock because of their rapid growth rate, CO2 fixation ability and high production capacity of lipids; they also do not compete with food or feed crops, and can be produced on non-arable land. Microalgae have broad bioenergy potential as they can be used to produce liquid transportation and heating fuels, such as biodiesel and bioethanol. In this review we present an overview about microalgae use for biodiesel and bioethanol production, including their cultivation, harvesting, and processing. The most used microalgal species for these purposes as well as the main microalgal cultivation systems (photobioreactors and open ponds) will also be discussed