Modeling, characterization and microalgal cultivation in an airlift panel photobioreactors.

Microalgae cultures are attracting great attentions in many industrial applications. However, one of the technical challenges is to cut down the capital and operational costs of microalgae production systems, with special difficulty in reactor design and scale-up. The thesis work open with an overview on the microalgae cultures as a possible answer to solve some of the upcoming planet issues and their applications in several fields. After the work offers a general outline on the state of the art of microalgae culture systems, taking a special look to the enclosed photobioreactors (PBRs). The overall objective of this study is to advance the knowledge of PBRs design and lead to innovative large scale processes of microalgae cultivation. An airlift flat panel photobioreactor was designed, modeled and experimentally characterized. The gas holdup, liquid flow velocity and oxygen mass transfer of the reactor were experimentally determined and mathematically modeled, and the performance of the reactor was tested by cultivation of microalgae. The model predicted data correlated well with experimental data, and the high concentration of suspension cell culture could be achieved with controlled conditions. The reactor was inoculated with the algal strain Scenedesmus obliquus sp. first and with Chlorella sp. later and sparged with air. The reactor was operated in batch mode and daily monitored for pH, temperature, and biomass concentration and activity. The productivity of the novel device was determined, suggesting the proposed design can be effectively and economically used in carbon dioxide mitigation technologies and in the production of algal biomass for biofuel and other bioproducts. Those research results favored the possibility of scaling the reactor up into industrial scales based on the models employed, and the potential advantages and disadvantages were discussed for this novel industrial design.

Synthesis and characterisation of hydrotalcite-like compounds for transesterification reaction

A series of templated [Mg(1-x)Alx(OH)2]x+(CO3)x/n2- with different structural properties have been synthesised using an alkali-free coprecipitation route. The macroporous materials were been obtained using two different kind of templating agents, polymeric materials, in order to cover a bigger size range (750-70 nm). All the materials have been characterized by different techniques: porosimetry, SEM-EDX, TEM-EDX, MP-AES, XRD, CO2 titration before and after the calcinations process. All the materials have been tested for transesterification reaction of C4-C8 triglycerides with methanol for biodiesel production.

Outdoor production of Isochrysis galbana (T-iso) in industrial scale photobioreactors and modelling of its photosynthesis and respiration rate

Isochrysis galbana is a widely-used strain in aquaculture in spite of its low productivity. To maximize the productivity of processes based on this microalgae strain, a model was developed considering the influence of irradiance, temperature, pH and dissolved oxygen concentration on the photosynthesis and respiration rate. Results demonstrate that this strain tolerates temperatures up to 35ºC but it is highly sensitive to irradiances higher than 500 µE·m-2·s-1 and dissolved oxygen concentrations higher than 11 mg·l-1. With the researcher group of the “Universidad de Almeria”, the developed model was validated using data from an industrial-scale outdoor tubular photobioreactor demonstrating that inadequate temperature and dissolved oxygen concentrations reduce productivity to half that which is maximal, according to light availability under real outdoor conditions. The developed model is a useful tool for managing working processes, especially in the development of new processes based on this strain and to take decisions regarding optimal control strategies. Also the outdoor production of Isochrysis galbana T-iso in industrial size tubular photobioreactors (3.0 m3) has been studied. Experiments were performed modifying the dilution rate and evaluating the biomass productivity and quality, in addition to the overall performance of the system. Results confirmed that T-iso can be produced outdoor at commercial scale in continuous mode, productivities up to 20 g·m-2·day-1 of biomass rich in proteins (45%) and lipids (25%) being obtained. The utilization of this type of photobioreactors allows controlling the contamination and pH of the cultures, but daily variation of solar radiation imposes the existence of inadequate dissolved oxygen concentration and temperature at which the cells are exposed to inside the reactor. Excessive dissolved oxygen reduced the biomass productivity to 68% of maximal, whereas inadequate temperature reduces to 63% of maximal. Thus, optimally controlling these parameters the biomass productivity can be duplicated. These results confirm the potential to produce this valuable strain at commercial scale in optimally designed/operated tubular photobioreactors as a biotechnological industry.

Bioactivity of extracts from extremophile microalgae Coccomyxa sp. on chloride cells in operculum tissue of Fundulus heteroclitus

Microalgae have been studied because of their great potential as a source of new compounds with important value for biotechnology and to understand their strategies of survival in extreme environments. The microalgae Coccomyxa sp., studied in this thesis, is a poly-extremophile witch was isolated from the acid mine drainage of S. Domingos mine. This environment is characterized by low pH (<3) and high concentration of metals, such as copper and iron. The main purpose of the present work was to evaluate the potential bioactivity in an ex-vivo animal model (Fundulus heteroclitus), and expression on selected genes, of cellular extracts obtained from cultures of Coccomyxa sp. at pH 7 without or with exposure to copper (0.6mM Cu²+). The extracts of Coccomyxa sp. cultured at pH 7 exposed to copper show a great potential to be used as epithelial NKCC inhibitors, revealing their potential use as diuretics, but did not show significant effects on gene expression. Coccomyxa sp. could be a good source of cellular extracts with a great potential to be used in pharmaceutical and biotechnology industries.

Effects of the inclusion of microalgae spirulina (Spirulina platensis) in the diet of Gilthead Sea bream (Sparus aurata) on growth and metabolism

In gilthead seabream aquaculture, the feed supplies in the market is very expensive due to its high content of animal protein. In this respect, spiruline appears to be a valuable substitute to animal and vegetable protein. In this study we performed two experiments. The scope of the first one was to determine the effect of the inclusion of Spirulina platensis hydrolyzed on the physiological state and growth in juveniles of Sparus aurata. A total of 180 individuals were fed for 128 days with three different feeds: control diet, diet with 2% of hydrolyzed microalgae (Sp2), and diet with 4% of hydrolyzed microalgae (Sp4).The experimental groups were tested in triplicate (except control group that was in duplicate). Biometric parameters were registered every two or three weeks. At the end of the experiment blood samples were collected to analyze plasma metabolites. After this we tried to evaluate the anti-oxidant response in animals remained from the first experiment using a toxicological assay with sodium nitrite lasting three days. Fish were divided into control, Spi 2% and Spi 4%, all them with and without NaNO2. Even then, the plasma metabolites data were collected after 24h and 72h. At the end of the first experiment the administration of S. platensis appeared to have a negative impact on growth of S. aurata respect the control feed. Furthermore, the lactate content registered showed a significant difference between the control and the spiruline administration. In the second experiment the spiruline feed showed a glucose and a lactate content with significant differences after 72h of exposition to nitrites respect the control group due to the interaction between nitrites and treatment. S. platensis hydrolyzed 2% and 4% do not seems a good substitution for S. aurata both as a growth enhancer and improver of health metabolic pathways. Its role as a good antioxidant has not been confirmed in these experiments.

Biodiesel ottenuto da olio di babassu e sue miscele: studio di produzione e controllo di qualità

Il contributo all’innalzamento del riscaldamento globale, prodotto dai combustibili fossili è un dei principali problemi ambientali. Le bioenergie potrebbero contribuire enormemente alla riduzione di questo fenomeno, sostituendo in parte i combustibili tradizionali di origine fossile. In questo contesto, può collocarsi il biodiesel prodotto a partire da oli vegetali, rappresentando una valida e strategica alternativa. Il biodiesel è una miscela di metil esteri di acidi grassi, [fatty acids methyl esters (FAME)], normalmente ottenuta tramite reazione di transesterificazione tra oli vegetali e alcol a catena corta in presenza di un catalizzatore acido o basico in catalisi sia omogena che eterogenea. Il biodiesel si colloca tra le materie prime di seconda generazione e può risultare una buona base di partenza per ottenere un biodiesel performante e con un basso costo finale.

Struttura filogenetica della comunità batterica associata ad Ostreopsis cf. Ovata in colture batch e dinamiche di crescita

Negli ultimi 10 anni i blooms attribuibili alla dinoflagellata bentonica Ostreopsis cf. ovata sono aumentati in termini di frequenza ed intensità lungo le coste del Mediterraneo, avendo ripercussioni negative sulla salute umana e forti impatti sulle comunità marine bentoniche, ciò a seguito della produzione di potenti tossine (composti palitossina-simili) da parte della microalga. Tra i fattori ecologici che innescano o regolano le dinamiche dei bloom tossici le interazioni tra microalghe e batteri sono in misura sempre maggiore oggetto di ricerca. In questo studio è stata analizzata la struttura filogenetica della comunità batterica associata ad O. cf. ovata in colture batch e valutate le dinamiche successionali della stessa in relazione alle differenti fasi di crescita della microalga (oltre che in relazione alle dinamiche di abbondanza virale). Lo studio filogenetico è stato effettuato tramite l’ausilio di metodiche molecolari di sequenziamento di next generation (Ion Torrent). Le abbondanze dei batteri e delle particelle virali sono state determinate tramite microscopia ad epifluorescenza; l’abbondanza cellulare algale è stata stimata tramite metodo Uthermohl. Il contributo della frazione batterica ad elevata attività respiratoria è stato determinato tramite doppia colorazione con coloranti DAPI e CTC. Dai dati emersi si evince che la comunità batterica attraversa due fasi di crescita distinte, una più marcata e concomitante con la fase esponenziale di O. cf. ovata, l'altra quando la microalga è in fase media stazionaria. Per quanto concerne la composizione filogenetica della comunità sono stati rilevati 12 phyla, 17 classi e 150 generi, sebbene i dati ottenuti abbiano rilevato una forte dominanza del phylum Proteobacteria con la classe Alphaproteobacteria, seguita dal phylum Bacteroidetes con la classe Sphingobacteria. Variazioni nella struttura filogenetica della comunità batterica, a livello di generi, tra le diverse fasi di crescita della microalga ha permesso di evidenziare ed ipotizzare particolari interazioni di tipo mutualistico e di tipo competitivo.

Biogas and bio-hydrogen: production and uses. A review

The first part of this essay aims at investigating the already available and promising technologies for the biogas and bio-hydrogen production from anaerobic digestion of different organic substrates. One strives to show all the peculiarities of this complicate process, such as continuity, number of stages, moisture, biomass preservation and rate of feeding. The main outcome of this part is the awareness of the huge amount of reactor configurations, each of which suitable for a few types of substrate and circumstance. Among the most remarkable results, one may consider first of all the wet continuous stirred tank reactors (CSTR), right to face the high waste production rate in urbanised and industrialised areas. Then, there is the up-flow anaerobic sludge blanket reactor (UASB), aimed at the biomass preservation in case of highly heterogeneous feedstock, which can also be treated in a wise co-digestion scheme. On the other hand, smaller and scattered rural realities can be served by either wet low-rate digesters for homogeneous agricultural by-products (e.g. fixed-dome) or the cheap dry batch reactors for lignocellulose waste and energy crops (e.g. hybrid batch-UASB). The biological and technical aspects raised during the first chapters are later supported with bibliographic research on the important and multifarious large-scale applications the products of the anaerobic digestion may have. After the upgrading techniques, particular care was devoted to their importance as biofuels, highlighting a further and more flexible solution consisting in the reforming to syngas. Then, one shows the electricity generation and the associated heat conversion, stressing on the high potential of fuel cells (FC) as electricity converters. Last but not least, both the use as vehicle fuel and the injection into the gas pipes are considered as promising applications. The consideration of the still important issues of the bio-hydrogen management (e.g. storage and delivery) may lead to the conclusion that it would be far more challenging to implement than bio-methane, which can potentially “inherit” the assets of the similar fossil natural gas. Thanks to the gathered knowledge, one devotes a chapter to the energetic and financial study of a hybrid power system supplied by biogas and made of different pieces of equipment (natural gas thermocatalitic unit, molten carbonate fuel cell and combined-cycle gas turbine structure). A parallel analysis on a bio-methane-fed CCGT system is carried out in order to compare the two solutions. Both studies show that the apparent inconvenience of the hybrid system actually emphasises the importance of extending the computations to a broader reality, i.e. the upstream processes for the biofuel production and the environmental/social drawbacks due to fossil-derived emissions. Thanks to this “boundary widening”, one can realise the hidden benefits of the hybrid over the CCGT system.

Studio dell'interazione di etanolo con catalizzatori TiO2-CeOx.

Due to the limited availability of natural oil and the harmful effects of its usage, the industry has focused in searching for sustainable types of raw materials for the production of chemicals. The bioethanol, obtained by fermentation of biomass, has gained particular importance in recent years both as a biofuel, and as a “building block” molecule because it can be considered as a starting reagent to obtain other added value chemical compounds, such as ethylene, acetaldehyde, butadiene and ethyl acetate. The goal of this research was the study of the interaction of ethanol with catalysts based on TiO2-CeOX. Since the electronic properties have implications on the catalytic activity, the idea was to understand if the TiO2-CeOX systems have different reactivity from that of ceria and rutile alone, or an intermediate between them. The study was focused on the characterization of the adsorbed species on the catalysts surface after ethanol adsorption through an in-situ spectroscopic technique (DRIFTS) that allowed us to extract information that could be helpful for the understanding of the processes at the molecular level. The mass spectrometry was used to monitor on-line the desorbed products. Furthermore, reactivity tests in a flow reactor were performed, in order to verify the catalytic behavior of the samples in conditions which are more similar to those applied at an industrial scale. The samples showed to behave in different way depending on the conditions used and the thermal treatment. The particular behavior of the mixed samples with respect to the single oxides is interpreted for each case according to the spectroscopic information collected.