Le concept d’une algoraffinerie primaire traitant les principaux composants de microalgues (lipides, protéines, glucides et pigments) a été étudié. Une séquence d'opérations unitaires a été mis en œuvre afin d'obtenir des fractions enrichies de ces biomolécules tout en conservant leur integrité dans le procédé en aval. L'étude a été principalement centrée sur Chlorella vulgaris, une espèce connue pour sa paroi cellulaire rigide. La majorité de la fraction lipophile (lipides et pigments) a été récupérée en utilisant du dioxyde de carbone supercritique avec de l'éthanol en tant que co-solvant, sans opération unitaire de cassage cellulaire préalable. La fraction hydrophile (protéines et polysaccharides) a été récupérée dans la phase aqueuse après broyage à billes comme méthode de cassage cellulaire. Par la suite, la phase aqueuse a été séparée en trois fractions par un procédé d'ultrafiltration en deux étapes. Ainsi, les amidons, les pigments, les protéines et les sucres ont été séparés les uns des autres avec succès. Une analyse du cycle de vie sera nécessaire pour estimer le coût et la durabilité du procédé de fractionnement. / A primary algorefinery, concept that deals with the main components of microalgae (lipids, proteins, carbohydrates and pigments), has been studied. A sequence of unit operations has been implemented in order to obtain separated enriched fractions of these biomolecules by conserving their integrity in the downstream process. The study was mainly centred on Chlorella vulgaris, a species known for its rigid cell wall. Most of the lipophilic fraction (lipids and pigments) was recovered using supercritical carbon dioxide with ethanol as a co-solvent, without a preliminary unit operation of cell disruption. The hydrophilic fraction (proteins and polysaccharides) was recovered in the aqueous phase after bed milling as cell disruption method. Subsequently, the aqueous phase was fractionated into three fractions by means of a process of two-stage ultrafiltration. Thus, starches, pigments, proteins and sugars were successfully separated from each other. A life cycle assessment will be necessary to estimate the cost and the sustainability of the fractionation process

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

Submitted in fulfillment for the requirements for the degree of Doctor of Technology: Biotechnology, Durban University of Technology, Durban, South Africa, 2015. / Main focus of this study is to investigate the enzymatic-conversion of microalgal lipids to biodiesel. However, preceding steps before conversion such as drying of microalgal biomass and extraction of lipids were also studied. Downstream processing of microalgae has several challenges and there is very little literature available in this area. S. obliquus was grown in the pilot scale open pond cultivation system for biomass production. Different techniques were studied for biomass drying and extraction of lipids from harvested microalgal biomass. Effect of these drying and extraction techniques on lipid yield and quality was assessed. Energy consumption and economic evaluation was also studied. Enzymatic conversion of microalgal lipids by extracellular and whole cell lipase application was investigated. For both applications, free and immobilized lipases from different sources were screened and selected based on biodiesel conversion. Process parameters were optimized using chosen extracellular and whole cell lipases; also step-wise methanol addition was studied to improve the biodiesel conversion. Immobilized lipase was studied for its reuse. Final biodiesel was characterized for its fuel properties and compared with the specifications given by international standards. Enzymatic conversion of microalgal lipids was compared with the conventional homogeneous acid-catalyzed conversion. Enzymatic conversion and chemical conversion were techno-economically investigated based on process cost, energy consumption and processing steps. Freeze drying was the most efficient technique, however at large scale economical sun drying could also be selected as possible drying step. Microwave assisted lipid extraction performed better compared to sonication technique. Immobilized P. fluorescens lipase in extracellular application and A. niger lipase in whole cell application showed superior biodiesel conversion. The extracellular immobilized P. fluorescens lipase showed better biodiesel conversion and yields than the immobilized A. niger whole cell lipase. Both the enzyme catalysts showed lower biodiesel conversion compared to conventional chemical catalyst and higher processing cost. However, techno-economic analysis showed that, the reuse potential of immobilized lipases can significantly improve the economics. Fewer purification steps, less wastewater generation and minimal energy input are the benefits of enzymatic route of biodiesel conversion. Microalgae as a feedstock and lipase as a catalyst for conversion makes overall biodiesel production process environmentally-friendly. Data from this study has academic as well as industrial significance. Conclusions from this study form the basis for greener and sustainable scaling-up of microalgal biodiesel production process. / D

Rampant increases in oil prices and detrimental effects of fossil fuels on the environment have been the main impetus for the development of environmentally friendly and sustainable energy sources. Amongst the many possibilities, microalgae have been proposed as a new alternative energy source to fossil fuels, as their growth is both sustainable and ecologically safe. By definition, microalgae are unicellular photosynthetic microorganisms containing chlorophyll a. These organisms are capable of producing large quantities of oils, surpassing that of traditional oil-seed crops, which can be transformed, through chemical processes, into biofuels such as biodiesel or bio-gasoline. Thus, recent research has gone into discovering high lipid producing algal strains, optimising growth media for increased lipid production and developing metabolic engineering to make microalgae a source of biofuel that is competitive to more traditional sources of biofuel and even to fossil fuel. In this context, the research reported here focused on using a mixotrophic growth mode as a way to increase lipid production for certain strains of microalgae. In addition, nitrogen starvation combined with mixotrophy was studied to analyse its effects on lipid production. Mixotrophy is the parallel usage of two trophic modes, in our case photoautotrophy and heterotrophy. Consequently, 12 algal strains were screened for mixotrophic growth, using glycerol as a carbon source. Glycerol is a waste product of the current biodiesel industry; it is a cheap and abundant carbon source present in many metabolic pathways. From this initial screening, several strains were chosen for subsequent experiments involving nitrogen starvation. Nitrogen starvation has been shown to induce lipid accumulation. The results obtained show that a mixotrophic growth mode, using glycerol as a carbon source, enhances lipid production for certain strains. Moreover, lipid enhancement was shown for nitrogen starvation combined with mixotrophic growth mode. This was dependant on time spent under nitrogen starvation and on initial concentrations of the nitrogen source. / L’augmentation effrénée des prix du pétrole et les effets néfastes des carburants fossiles sur l’environnement sont les raisons principales pour la recherche et le développement de nouvelles sources d’énergie durables et écologiques. Parmi de grands nombres de possibilités, les micro-algues sont proposées comme une source alternative d’énergie aux carburants fossiles, étant donné que leur croissance est durable et écologique. Les micro-algues sont des organismes unicellulaires et photosynthétiques détenant comme pigment essentiel la chlorophylle a. Ces organismes sont capables de produire de grandes quantités d’huile, parfois excédant celles des cultures agricoles traditionnellement utilisées pour les biocarburants. Ces huiles peuvent être transformées en biocarburants, tel que le biodiésel et le bio-essence, par certains procédés chimiques. La recherche actuelle est basée sur la découverte de souches d’algues capables de produire un haut rendement de lipides, l’optimisation de milieux de croissance pour accroitre la production lipidique et la manipulation génomique afin de créer des souches de micro-algues dont les rendements peuvent rivaliser avec l’agriculture tradionnelle et même les carburants fossiles. Dans ce contexte, notre recherche se concentre sur l’utilisation d’un mode de croissance mixotrophe afin d’induire une augmentation dans la production lipidique de certaines souches de micro-algues. De plus, des études sur la carence en azote combinée à la croissance mixotrophe ont été entreprises pour évaluer l’effet de ces paramètres sur la production lipidique. La mixotrophie est un mode de croissance qui utilise en parallèle deux modes trophiques différents, tel que l’hétérotrophie et l’autotrophie. De ce fait, 12 souches d’algues ont été examinées pour leur capacité à croitre dans un milieu mixotrophe. Le glycérol est un produit secondaire de l’industrie du biodiésel actuelle. Cette substance est à bas prix, abondante et peut être utilisé comme substrat dans plusieurs voies métaboliques. Du criblage initial, plusieurs souches ont été choisies pour des expériences subséquentes impliquant la carence en azote. La carence en azote à été démontrer comme un déclencheur de l’accumulation de lipide chez les micro-algues dans des recherches antérieures. Les résultats obtenus démontrent que la croissance mixotrophe permet d’augmenter la production de lipide chez certaines souches. De plus, la carence en azote combinée à la croissance mixotrophe a permis d’augmenter la production lipidique. Cependant, celle-ci dépendait du temps passer en carence et des concentrations initiales de source d’azote.

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O uso de microalgas e cianobactérias para a produção de biocombustíveis e outros produtos e matérias-primas de interesse comercial tem sido amplamente divulgado como uma tecnologia sustentável bastante promissora, em função das elevadas produtividades areais, potencial para fixação de CO2, uso de terras não adequadas para cultivo e possibilidade de utilizar fontes alternativas de nutrientes, tais como água salobra ou efluentes agroindustriais. A produção comercial de cianobactérias em tanques abertos em formato de pista foi estudada combinando-se a modelagem matemática do crescimento nos tanques com a avaliação técnica, econômica e de sustentabilidade do processo. Construiu-se um macromodelo para a simulação dos tanques, que permitiu determinar o impacto de variáveis ambientais como, por exemplo, temperatura e luminosidade, e otimizar condições de operação e coleta. A análise econômica detalhada demonstrou o impacto dos custos de capital, operação e consumo de energia pelo processo, também destacando a importância da receita de produtos de alto valor agregado para a viabilidade do sistema, com base na tecnologia atual. Os valores de transformidade e índices de sustentabilidade e carga ambiental, obtidos através da análise emergética, são comparáveis com outros processos para obtenção de biocombustíveis de segunda geração, mas os elevados custos de construção e operação e grande consumo de energia nas etapas de coleta e extração representam ainda grandes desafios à sua sustentabilidade. A análise de sensibilidade para as principais variáveis de processo e estudos de caso para melhorias e modelos de negócio alternativos permitiram priorizar áreas para pesquisa futura com base no impacto econômico e ambiental. / The use of microalgae and cyanobacteria for the production of biofuels and other substances of commercial interest has been widely advertised as an extremely promising sustainable technology, due to the high areal productivity, potential for fixation of CO2, possibility of using non-arable land and alternative sources of nutrients such as brackish water and agricultural and industrial effluents. The commercial production of cyanobacteria in open raceway ponds was studied through the combination of a mathematical model for the algal growth with technical, economical and sustainability evaluations. A macromodel was developed to simulate the ponds, and it was used to assess the impact of environmental variables, such as light and temperature, and to optimize the process conditions for operation and harvesting. A detailed economic analysis demonstrated the impact of capital, operation costs and energy consumption, also highlighting the importance of revenue from high value products to process viability, considering the current technology. The transformity, emergy sustainability and environmental loading indices obtained by emergy analysis are comparable to other second generation biofuels, but the high construction and operation costs and energy consumption by the harvesting and extraction steps still represent major challenges to sustainability. The sensitivity analysis and evaluation of both technology improvements and alternative business models enabled the prioritization of future research areas, based on economic and environmental impact.

Os ensaios ecotoxicológicos com o fitoplâncton marinho têm sido uma importante ferramenta para o monitoramento da qualidade de águas devido à sua relevância ecológica. A variabilidade dos resultados dos ensaios ecotoxicológicos também pode ser atribuída à sensibilidade do lote de organismos-teste. O presente trabalho traz informações da sensibilidade de Dunaliella tertiolecta para as substâncias de referências, dicromato de potássio, dodecil sulfato de sódio, cromato de potássio, sulfato de zinco e sulfato de cobre, e dois métodos de determinação da biomassa. As concentrações inibitórias com a densidade celular foram CI50-48h= 177,1, CI50-72h= 129,8 e CI50-96h= 108,5 mg/L de K2Cr2O7; CI50-48h= 0,97, CI50-72h= 1,25 e CI50-96h= 1,18mg/L de DSS e CI50-96h= 273,3mg/L de K2CrO4. Para o conteúdo de clorofila-a (96h), foram CI50-Cl-a= 113,0mg/L de K2Cr2O7; CI50-Cl-a= 1,26mg/L de DSS e CI50-Cl-a= 150,6mg/L de K2CrO4. A sensibilidade da microalga foi maior ao DSS, altamente degradável, em relação aos compostos metálicos, com potencial carcinogênico. As 96h de exposição resultaram em melhor repetibilidade, não havendo diferença significativa entre os métodos utilizados. Na seleção da substância de referência e do método também devem ser considerados os resíduos gerados e a periculosidade dos reagentes, visando à qualidade dos resultados e um menor impacto ao ambiente / The toxicity tests with marine phytoplankton have been an important tool for the water quality monitoring due to its ecological relevance. The variability of the toxicity tests results can also be attributed to the test-organisms batch sensitivity. This study provides information about the sensitivity of Dunaliella tertiolecta to the reference substances potassium dichromate, sodium dodecyl sulfate, potassium chromate, zinc sulfate and copper sulfate, and two methods of biomass determination. The inhibitory concentrations were IC50-48h= 177.1, IC50-72h= 129.8 and IC50-96h= 108.5mg/L of K2Cr2O7; IC50-48h= 0.97, IC50-72h= 1.25 and IC50-96h= 1.18mg/L of DSS and IC50-96h= 273,3mg/L of K2CrO4. For the chlorophyll-a content (96h) were IC50-Cl-a= 113.0mg/L of K2Cr2O7, IC50-Cl-a= 1.26mg/L of SDS and IC50-Cl-a= 150,6mg/L of K2CrO4. The microalgae sensibility was higher to DSS, highly degradable related to metallic compounds, with carcinogenic potential. The 96h of exposure resulted in better repeatability, with no significant difference between the tested methods. In the reference substance and method selection the generated residues and the hazard reagent must be considered, due to the results quality and a lower impact on the ambient.

As microalgas são candidatas promissoras para a produção em larga escala de biocombustíveis devido a sua alta eficiência fotossintética. No entanto, os custos relativamente altos de produção por baixas produtividades em lipídios têm sido um dos principais obstáculos que impedem sua produção comercial. Portanto, é necessário focar a pesquisa no aumento da biomassa e na produtividade em lipídios, através do desenvolvimento de biorreatores e técnicas de cultivo inovadoras. Numa primeira fase, este estudo mostra a otimização dos regimes de adição de nutrientes no cultivo de Neochloris oleoabundans em fotobiorreatores tubulares, determinando que a melhor metodologia de adição de CO2 é adicionando-o de forma intermitente e automatizada, enquanto que o melhor processo de alimentação de nitrogênio é por meio de um processo em batelada alimentada tomando como uma referência a produtividade diária de biomassa. Na segunda etapa, foi testada a influência de agentes estressores adicionados ao cultivo sob carência de nitrogênio, tais como tiossulfato de sódio como agente redutor e cloreto de sódio e glicerina como agentes de choque osmótico, buscando um acúmulo de lipídios na biomassa. Os resultados mostraram que o tiossulfato de sódio em 1,2 mM e o cloreto de sódio em 2,2 mM aumentaram o total de lipídios em 21% e 25%, respectivamente. Finalmente, foram testados diferentes regimes de luz, com um esquema 12:12, sendo 12 horas de luz fluorescente e 12 horas com um sistema distinto: escuro, diodos emissores de luz (LED) vermelha e LED branca. Os melhores resultados foram obtidos com LED branca, com um acúmulo de lipídios de até 27% da biomassa seca e uma concentração final de células de 2335mg/L, estabelecendo assim um método de iluminação econômica com alta produtividade (145mg / L dia). / Microalgae are promising candidates for large-scale global biofuel production because of their high photosynthetic efficiency. However, relatively high production costs due to low lipid productivity have been one of the major obstacles impeding their commercial production. Therefore, it is necessary to accurate the research into an increase in biomass and oil productivity, by means of novel bioreactors\' design and cultivation techniques. On a first stage, this study shows the optimization of nutrients\' addition regimes in Neochloris oleoabundans cultivation in tubular photobioreactors, finding that the best CO2 addition methodology is an automatized intermittent adding and the best feeding process for nitrogen is a fed-batch process taking as a reference the daily biomass productivity. On the second step, it was tested the influence of stressing agents added to the culture under nitrogen starvation, such as sodium thiosulphate for reducing environment and sodium chloride and glycerol for osmotic shock, aiming lipid accumulation in the biomass. The results showed that sodium thiosulphate at 1,2mM and sodium chloride at 2,2mM raised the total lipids up to 21% and 25% respectively. Finally, there were tested different light regimes, with a scheme 12:12, being 12 hours of fluorescent light and 12 hours of a singular system: dark, red light-emitting-diodes (LED) and white LED. The best results were obtained with white LED, with an accumulation up to 27% of dry biomass and a final cell concentration up to 2335mg/L, establishing an economic illumination method with high productivity.

Les champs électriques pulsés (CEP) offrent un réel intérêt dans le cadre de la traite des microalgues. En effet, ils permettent l'extraction sélective des composés hydrosolubles ou l'utilisation de solvants biocompatibles pour récolter les molécules hydrophobes. La viabilité des microalgues peut ainsi être conservée. L'objectif de ce travail de thèse est de définir des conditions de traitement permettant à la fois l'extraction des composés d'intérêt et le maintien de la viabilité des microalgues. Le modèle d'étude est la microalgue verte Haematococcus pluvialis. Au stade végétatif, celle-ci contient près d'un tiers de son poids de matière sèche en protéines et en conditions stressantes, elle accumule de l'astaxanthine, un caroténoïde à haute valeur ajoutée.L'application de CEP de 1 kV.cm-1 permet de collecter 50 % des protéines extractibles par broyage avec des microbilles. La mesure de cinq paramètres biologiques suite à ce traitement a mis en évidence que les cellules retrouvaient un état physiologique comparable à celui de microalgues non traitées au bout de 72 h. Cette condition de traitement constitue donc un bon compromis entre l'extraction des protéines et la survie des microalgues, ce qui renforce la faisabilité d'une traite de microalgues par CEP.Dans le cadre de l'extraction de l'astaxanthine, la paroi très résistante des kystes constitue le principal verrou à lever. Une optimisation des conditions de traitement (en particulier de la force des impulsions) et du stade cellulaire traité représentent les deux principales perspectives à étudier pour que l'utilisation des CEP dans le cadre de l'extraction de l'astaxanthine soit pertinente. / Pulsed electric fields (PEF) offer a real interest for microalgae milking. Indeed, they allow the selective extraction of water-soluble compounds or the use of biocompatible solvents to harvest the hydrophobic molecules. The viability of microalgae can thus be maintained. The aim of this PhD thesis work is to define the treatment conditions allowing both the extraction of compounds of interest and the maintenance of the microalgae viability. The biological model is the green microalga Haematococcus pluvialis. At the vegetative stage, it contains nearly one third of its dry matter weight in proteins and under stressful conditions, it accumulates astaxanthin, a high added value carotenoid.The application of PEF of 1 kV.cm-1 allows to collect 50% of the proteins extractable by bead milling. The measurement of five biological parameters highlights that treated cells recover a physiological state comparable to that of untreated microalgae after 72h. This treatment condition constitutes therefore a good compromise between the protein extraction and the survival of the microalgae, which reinforces the feasibility of microalgae milking by PEF.Within the context of astaxanthin extraction, the high resistance of the cell wall of the cysts constitutes the main limitation. Optimization of the treatment conditions (particularly pulse strength) and the cellular stage to treat represent the two main perspectives to study for the use of PEF for astaxanthin extraction to be relevant.

O uso de microalgas e cianobactérias para a produção de biocombustíveis e outros produtos e matérias-primas de interesse comercial tem sido amplamente divulgado como uma tecnologia sustentável bastante promissora, em função das elevadas produtividades areais, potencial para fixação de CO2, uso de terras não adequadas para cultivo e possibilidade de utilizar fontes alternativas de nutrientes, tais como água salobra ou efluentes agroindustriais. A produção comercial de cianobactérias em tanques abertos em formato de pista foi estudada combinando-se a modelagem matemática do crescimento nos tanques com a avaliação técnica, econômica e de sustentabilidade do processo. Construiu-se um macromodelo para a simulação dos tanques, que permitiu determinar o impacto de variáveis ambientais como, por exemplo, temperatura e luminosidade, e otimizar condições de operação e coleta. A análise econômica detalhada demonstrou o impacto dos custos de capital, operação e consumo de energia pelo processo, também destacando a importância da receita de produtos de alto valor agregado para a viabilidade do sistema, com base na tecnologia atual. Os valores de transformidade e índices de sustentabilidade e carga ambiental, obtidos através da análise emergética, são comparáveis com outros processos para obtenção de biocombustíveis de segunda geração, mas os elevados custos de construção e operação e grande consumo de energia nas etapas de coleta e extração representam ainda grandes desafios à sua sustentabilidade. A análise de sensibilidade para as principais variáveis de processo e estudos de caso para melhorias e modelos de negócio alternativos permitiram priorizar áreas para pesquisa futura com base no impacto econômico e ambiental. / The use of microalgae and cyanobacteria for the production of biofuels and other substances of commercial interest has been widely advertised as an extremely promising sustainable technology, due to the high areal productivity, potential for fixation of CO2, possibility of using non-arable land and alternative sources of nutrients such as brackish water and agricultural and industrial effluents. The commercial production of cyanobacteria in open raceway ponds was studied through the combination of a mathematical model for the algal growth with technical, economical and sustainability evaluations. A macromodel was developed to simulate the ponds, and it was used to assess the impact of environmental variables, such as light and temperature, and to optimize the process conditions for operation and harvesting. A detailed economic analysis demonstrated the impact of capital, operation costs and energy consumption, also highlighting the importance of revenue from high value products to process viability, considering the current technology. The transformity, emergy sustainability and environmental loading indices obtained by emergy analysis are comparable to other second generation biofuels, but the high construction and operation costs and energy consumption by the harvesting and extraction steps still represent major challenges to sustainability. The sensitivity analysis and evaluation of both technology improvements and alternative business models enabled the prioritization of future research areas, based on economic and environmental impact.