Thesis (PhD (Chemical Engineering))--Cape Peninsula University of Technology, 2019 / The South African wine industry is constantly facing several challenges which affect the quality of wine, the local/global demand and consequently the revenue generated. These challenges include the ongoing drought, bush fires, climate change and several liquor amendment bills aimed at reducing alcohol consumption and alcohol outlets in South Africa. It is therefore critical for the wine industry to expand and find alternative ways in which sub-standard or surplus wine grapes can be used to prevent income losses and increase employment opportunities. Traditional Balsamic Vinegar (TBV) is a geographically and legislative protected product produced only in a small region in Italy. However, the methodology can be used to produce similar vinegars in other regions. Balsamic-styled vinegar (BSV), as defined in this thesis, is a vinegar produced by partially following the methods of TBV while applying process augmentation techniques. Balsamic-styled vinegar is proposed to be a suitable product of sub-standard quality or surplus wine grapes in South Africa. However, the production of BSV necessitates the use of cooked (high sugar) grape must which is a less favourable environment to the microorganisms used during fermentation. Factors that negatively affect the survival of the microorganisms include low water activity due to the cooking, high osmotic pressure and high acidity. To counteract these effects, methods to improve the survival of the non-Saccharomyces yeasts and acetic acid bacteria used are essential. The primary aim of this study was to investigate several BSV process augmentation techniques such as, aeration, agitation, cell immobilization, immobilized cell reusability and oxygen mass transfer kinetics in order to improve the performance of the microbial consortium used during BSV production. The work for this study was divided into four (4) phases. For all the phases a microbial consortium consisting of non-Saccharomyces yeasts (n=5) and acetic acid bacteria (n=5) was used. Inoculation of the yeast and bacteria occurred simultaneously. The 1st phase of the study entailed evaluating the effect of cells immobilized by gel entrapment in Ca-alginate beads alongside with free-floating cells (FFC) during the production of BSV. Two Ca-alginate bead sizes were tested i.e. small (4.5 mm) and large (8.5 mm) beads to evaluate the effects of surface area or bead size on the overall acetification rates. Ca-alginate beads and FFC fermentations were also evaluated under static and agitated (135 rpm) conditions. The 2nd phase of the study involved studying the cell adsorption technique for cell immobilization which was carried-out using corncobs (CC) and oak wood chips (OWC), while comparing to FFC fermentations. At this phase of the study, other vinegar bioreactor parameters such as agitation and aeration were studied in contrast to static fermentations. One agitation setting (135 rpm) and two aeration settings were tested i.e. high (0.3 vvm min−1) and low (0.15 vvm min−1) aeration conditions. Furthermore, to assess the variations in cell adsorption capabilities among individual yeast and AAB cells, the quantification of cells adsorbed on CC and OWC prior- and post-fermentation was conducted using the dry cell weight method. The 3rd phase of the study entailed evaluating the reusability abilities of all the matrices (small Ca-alginate beads, CC and OWC) for successive fermentations. The immobilized cells were evaluated for reusability on two cycles of fermentation under static conditions. Furthermore, the matrices used for cell immobilization were further analysed for structure integrity by scanning electron microscopy (SEM) before and after the 1st cycle of fermentations. The 3rd phase of the study also involved the sensorial (aroma and taste) evaluations of the BSV’s obtained from the 1st cycle of fermentation in order to understand the sensorial effects of the Ca-alginate beads, CC and OWC on the final BSV. The 4th phase of the study investigated oxygen mass transfer kinetics during non-aerated and aerated BSV fermentation. The dynamic method was used to generate several dissolved oxygen profiles at different stages of the fermentation. Consequently, the data obtained from the dynamic method was used to compute several oxygen mass transfer parameters, these include oxygen uptake rate ( 𝑟𝑟𝑂𝑂2 ), the stoichiometric coefficient of oxygen consumption vs acid yield (𝑌𝑌𝑂𝑂/𝐴𝐴), the oxygen transfer rate (𝑁𝑁𝑂𝑂2 ), and the volumetric mass transfer coefficients (𝐾𝐾𝐿𝐿𝑎𝑎). During all the phases of the study samples were extracted on weekly intervals to evaluate pH, sugar, salinity, alcohol and total acidity using several analytical instruments. The 4th phase of the study involved additional analytical tools, i.e. an oxygen µsensor to evaluate dissolved oxygen and the ‘Speedy breedy’ to measure the respiratory activity of the microbial consortium used during fermentation. The data obtained from the 1st phase of the study demonstrated that smaller Ca-alginate beads resulted in higher (4.0 g L-1 day−1) acetification rates compared to larger (3.0 g L-1 day−1) beads, while freely suspended cells resulted in the lowest (0.6 g L-1 day−1) acetification rates. The results showed that the surface area of the beads had a substantial impact on the acetification rates when gel entrapped cells were used for BSV fermentation. The 2nd phase results showed high acetification rates (2.7 g L-1 day−1) for cells immobilized on CC in contrast to cells immobilized on OWC and FFC, which resulted in similar and lower acetification rates. Agitated fermentations were unsuccessful for all the treatments (CC, OWC and FFC) studied. Agitation was therefore assumed to have promoted cell shear stress causing insufficient acetification during fermentations. Low aerated fermentations resulted in better acetification rates between 1.45–1.56 g L-1 day−1 for CC, OWC and FFC. At a higher aeration setting, only free-floating cells were able to complete fermentations with an acetification rate of 1.2 g L-1 day−1. Furthermore, the adsorption competence data showed successful adsorption on CC and OWC for both yeasts and AAB with variations in adsorption efficiencies, whereby OWC displayed a lower cell adsorption capability compared to CC. On the other hand, OWC were less efficient adsorbents due to their smooth surface, while the rough surface and porosity of CC led to improved adsorption and, therefore, enhanced acetification rates. The 3rd phase results showed a substantial decline in acetification rates on the 2nd cycle of fermentations when cells immobilized on CC and OWC were reused. While cells entrapped in Ca-alginate beads were able to complete the 2nd cycle of fermentations at reduced acetification rates compared to the 1st cycle of fermentations. The sensory results showed positive ratings for BSV’s produced using cells immobilized in Ca-alginate beads and CC. However, BSV’s produced using OWC treatments were neither ‘liked nor disliked’ by the judges. The SEM imaging results further showed a substantial loss of structural integrity for Ca-alginate beads after the 1st cycle fermentations, with minor changes in structural integrity of CC being observed after the 1st cycle fermentations. OWC displayed the same morphological structure before and after the 1st cycle fermentations which was attributed to their robustness. Although Ca-alginate beads showed a loss in structural integrity, it was still assumed that Ca-alginate beads provided better protection against the harsh environmental conditions in contrast to CC and OWC adsorbents due to the acetification rates obtained on both cycles. The 4th phase data obtained from the computations showed that non-aerated fermentations had a higher 𝑌𝑌𝑂𝑂/𝐴𝐴, 𝑟𝑟𝑂𝑂2 , 𝑁𝑁𝑂𝑂2 and a higher 𝐾𝐾𝐿𝐿𝑎𝑎 . It was clear that aerated fermentations had a lower aeration capacity due to an inappropriate aeration system design and an inappropriate fermentor. Consequently, aeration led to several detrimental biochemical changes in the fermentation medium thus affecting 𝐾𝐾𝐿𝐿𝑎𝑎 and several oxygen mass transfer parameters which serve as a driving force. Overall, it was concluded that the best method for BSV production is the use of cells entrapped in small alginate beads or cells adsorbed on CC under static and non-aerated fermentations. This conclusion was based on several factors such as cell affinity/cell protection, acetification rates, fermentation period and sensorial contributions. However, cells entrapped in Ca-alginate beads had the highest acetification rates. The oxygen mass transfer computations demonstrated a high 𝐾𝐾𝐿𝐿𝑎𝑎 when Ca-alginate beads were used under static-non-aerated conditions compared to fermentations treated with CC. Therefore, a fermentor with a high aeration capacity needs to be designed to best suit the two BSV production systems (Ca-alginate beads and CC). It is also crucial to develop methods which can increase the robustness of Ca-alginate beads in order to improve cell retention and reduce the loss of structural integrity for subsequent cycles of fermentation. Studies to define parameters used for upscaling the BSV production process for large scale productions are also crucial.

No description available.

Syftet med detta masterprojekt var att undersöka möjligheten att använda biobaserat, mjukgjort natriumalginat (NaAlg) som enzymbärare. Alginaterna görs traditionellt bearbetbara genom att tillsätta olika mjukgörare, såsom polyoler (glycerol, sorbitol, etc.), i detta arbete användes glycerol. Den experimentella aspekten av projektet involverade beredning i laboratorieskala av prover, som omfattade blandning, varmpressning, potentiell behandling med nedsänkning i kalciumbad och efterföljande torkning. Förlusten av kemikalier under bearbetningen kvantifierades med hjälp av termogravimetrisk analys (TGA) och ultraviolett-synlig spektroskopi (UV-Vis). De preparerade bearbetade proverna karakteriserades genom extraktionsexperiment. Under den första halvan av projektet undersöktes färgämnesladdningen av proverna för enkelhets skull. Senare byttes den laddade föreningen ut mot enzymer. UV-Vis-mätningar användes i båda fallen för att effektivt karakterisera proverna. De initialt preparerade mjukgjorda natriumalginatproverna var för känsliga och löstes lätt i vatten. Följaktligen utfördes experiment för att förbättra stabiliteten hos matrisen till en tillräcklig nivå genom jonbyte av natriumjoner till kalciumjoner. Denna process förbättrade avsevärt vattenstabiliteten hos proverna. Av resultaten verkar det som om frisättningen av den laddade föreningen kan kontrolleras genom jonbytesbehandlingen. När väl förbättrad vattenstabilitet hos matrisen upptäcktes, undersöktes effekten av mjukningsmedlet genom att ändra blandningsförhållandet för glycerol. Det visade sig att nivån av glycerol i provet är omvänt proportionell mot den laddade föreningens återhållbarhet. De enzymladdade proverna implementerades först med användning av lipasenzymer på grund av att de var lättillgängliga i laboratoriet. Inom kort visade det sig att analysen för att kvantifiera lipasaktivitet utförs i 2-metyl-2-butanol (2M2B), vilket inte orsakade någon svullnad i proverna som observerats tidigare. Därför byttes det laddade enzymet till Horseradish Peroxidase (HRP). Det visade sig att HRP-laddade prover hade aktivitet efter bearbetning. De vattenstabiliserade HRP-laddade proverna hade mätbar aktivitet under fyra timmars exponering för analysen. Förutom enzymatisk analys övervakades frisättningsprofilen för protein också med användning av Bradford-analysen. Man såg att efter en initial måttlig frisättning av enzymerna, planade frisättningen ut och upphörde efter fyra timmar. Resultaten av Bradford-analysen överensstämde med de enzymatiska aktivitetsmätningarna. Det bör noteras att den ursprungliga formuleringen av projektet var starkt baserad på en nyligen utvecklad bearbetningsmetod, extrudering för alginatkompositer. Tyvärr gjordes inga tester med extrudering på grund av tekniska svårigheter med instrumentet. / The aim of this master project was to investigate the possibility to use bio-based, plasticized sodium alginate (NaAlg) as enzyme carrier. The alginates are traditionally made processable by adding various plasticizers, such as polyols (glycerol, sorbitol, etc.), in this work glycerol was used. The experimental aspect of the project involved the lab-scale preparation of samples, which encompassed compounding, hot pressing, potential treatment with a calcium bath immersion, and subsequent drying. The loss of chemicals during processing was quantified using Thermogravimetric analysis (TGA) and Ultraviolet-Visible spectroscopy (UV-Vis). The prepared processed samples were characterized by extraction experiments. In the first half of the project, the colorant loading of the samples was investigated for simplicity. Later the loaded compound was exchanged for enzymes. UV-Vis measurements were employed in both cases to characterize the samples effectively. The initially prepared plasticized sodium alginate samples were too sensitive and readily dissolved in water. Consequently, experiments were performed to improve the stability of the matrix to a sufficient level by ion exchange of sodium ions to calcium ions. This process significantly improved the water stability of the samples. From the results, it seems the release of the loaded compound can be controlled by the ion exchange treatment. Once enhanced water stability of the matrix was found, the effect of the plasticizer was investigated by changing the mixing ratio of glycerol. It was found that the level of glycerol in the sample is inversely proportional to the restrainability of the loaded compound. The enzyme loaded samples first were implemented by the use of lipase enzymes due to being readily available in the laboratory. Shortly, it was found that the assay to quantify lipase activity is performed in 2-methyl-2-butanol (2M2B), which did not cause any swelling in the samples as observed before. Therefore, the loaded enzyme was switched to Horseradish Peroxidase (HRP). It was found that HRP loaded samples possessed activity after processing. The water stabilized HRP loaded samples possessed measurable activity over four hours of exposure to the assay. In addition to enzymatic assay, the release profile of protein was also monitored using Bradford assay. It was seen that after an initial moderate release of the enzymes, the release leveled off and stopped after four hours. The results of the Bradford assay aligned with the enzymatic activity measurements. It should be noted, that the original formulation of the project was heavily based on arecently developed processing method, extrusion for alginate composites. Unfortunately,no tests were performed with extrusion due to technical difficulties with the instrument.

No description available.

The use of cell transplantation to treat enzyme deficiency disorders is limited by the immune response targeted against foreign tissue or the use of life-long immunosuppressants. Hiding cells from the immune system in an encapsulation device is promising. Cells encapsulated within an anionic calcium alginate hydrogel bead are protected through a semi-permeable membrane formed by polycation, poly-L-lysine (PLL). A final layer of alginate is added to hide the cationic PLL surface but this has proved to be difficult creating capsules which are prone to fibrotic overgrowth, blocking exchange of nutrients, waste and therapeutic enzymes through the capsule. For long term applications these capsules need to be both biocompatible and mechanically robust. This thesis aims to address the biocompatibility issue of high cationic surface charge by synthesizing polycations of reduced charge using N-(3- aminopropyl)methacrylamide hydrochloride (APM) and N-(2- hydroxypropyl)methacrylamide (HPM) and study the associated mechanical properties of the capsules using micropipette aspiration. Micropipette aspiration was applied and validated for alginate based capsules (gel and liquid core) to quantify stiffness. Varying ratios of APM were used to control the overall charge of the polycations formed while HPM was incorporated as a neutral, hydrophilic, nonfouling comonomer. The molecular weight (MW) was controlled by using reversible addition-fragmentation chain transfer (RAFT) polymerization. The biocompatibility of these polymers was tested by cell adhesion and proliferation of 3T3 fibroblasts onto APM/HPM copolymer functionalized surfaces and by solution toxicity against C2C12 myoblasts. The ability for the APM/HPM copolymers to bind to alginate and form capsules was also assessed, along with the integrity and stiffness of the capsule membrane with or without additional covalent cross-linking by reactive polyanion, poly(methacrylic acid-co-2-vinyl-4,4- dimethylazlactone) (PMV60). Thermo-responsive block copolymers of N-isopropylacrylamide (NIPAM) and 2- hydroxyethylacrylamide (HEA) were also synthesized as potential drug delivery nanoparticles, showing control over micelle morphology with varying NIPAM to HEA ratios. / Thesis / Doctor of Science (PhD) / The treatment of enzyme deficiency disorders by cell transplantation is limited by the immune attack of foreign tissue in absence of immunosuppressants. Cells protected in an encapsulation device has shown promise. Poly-L-lysine, a widely used membrane material in these protective capsules, binds to the anionic gel entrapping living cells because it is highly cationic. The high cationic charge is difficult to hide causing the immune system to build tissue around the capsule, preventing the encapsulated cells from exchanging nutrients and therapeutic enzymes. This thesis aims to replace poly-L-lysine by synthesizing a series of more biocompatible materials of decreasing cationic charge. These materials were studied for the ability to support tissue growth and form stable capsules. The membrane strength was measured using an aspiration method validated for these types of capsules. Reducing the cationic charge of the materials increased the biocompatibility of the capsule membrane but also made for weaker membranes.

An ink made of alginate and methylcellulose with embedded magnetite microparticles was developed for extrusion printing. Constructs, so-called scaffolds, are colonised with cells which can be activated by mechanical stimulation. In this work, a defined magnetic field gradient is applied to achieve non-contact deformation. However, the deformation behaviour or relevant material parameters of the hybrid material are unknown. While the properties were determined with experiments adapted to hydrogels, a separate experimental set-up for micro-computed tomography, adapting the Maxwell configuration, was developed to investigate the deformation behaviour. These analyses were performed depending on ageing and particle concentration. For these tests, strands were used as bending beams, since these are simple and well known systems. Firstly, a model for the bending curve was erected, which defines a range in which the real bending curve would be expected. It was compared with the measured bending curves. There was very good agreement for the first days. On day 14, the measured bending curves were still within the calculated range, but at the lower limit due to the shortcomings of the model as the violation of the small deformations condition at this point. Secondly, the bending as a function of incubation duration was observed by a series of radiograms when a magnetic field gradient was applied. From this, a functional approach was formulated to describe the system response. Some parameters have already been identified, for others a proposal is given. Thirdly, microscopic analyses were carried out to observe the effects of the field gradient on particle distribution and structure. It was revealed that a homogeneous particle distribution was found even after 2.5 h. Also, in the direction of the field gradient, no chains were formed and no damage of the network could be detected. The obtained results show, that the material is suitable for mechanical stimulation.

Ce travail de recherche s'intègre dans un projet de développement d'un procédé de traitement des effluents par séparation magnétique s'inscrivant dans une démarche d'écoconception. Pour ce faire, nous avons préparé des billes d'alginate encapsulant des nanoparticules magnétiques et du charbon actif. Les matériaux composant ces billes possèdent des propriétés adsorbantes permettant l'extraction de polluants ; leurs propriétés magnétiques permettent de les séparer magnétiquement de l'effluent à traiter. La formulation et la caractérisation des billes magnétiques est le point essentiel de ce travail. Différentes formulations ont été testées en modifiant les quantités de matériaux précurseurs ainsi que le mode de réticulation de l'alginate. Les capacités d'adsorption des billes vis-à-vis de deux colorants utilisés comme modèles de polluant organique, le bleu de méthylène et le méthyl orange, ont été étudiées. La modélisation des isothermes d'adsorption a permis également de comprendre les mécanismes mis en jeu. Les cinétiques d'adsorption ont également été étudiées et modélisées.

Deux systèmes aqueux à 20°C constitués de protéines globulaires de pois et d'alginate de sodium ont été considérés au cours de cette étude, dans des conditions de solvant fixées à pH 7,2 et 0,1 M NaCl. Dans un premier temps, le comportement de phase de globulines faiblement dénaturées (i) ou pré-agrégées thermiquement (ii) en mélange avec de l'alginate a été comparé à différentes échelles d'observation, en termes de diagrammes de phase et de microstructure analysée par microscopie confocale. Attribuée à un phénomène général d'incompatibilité thermodynamique, la séparation de phase a été décrite tout particulièrement sous des aspects morphologiques et cinétiques à l'échelle microscopique, selon la composition de départ en biopolymères et le mode de préparation des globulines. Par la suite, une gélification de chacun des deux systèmes a été opérée à froid, par libération de calcium ionique in situ à partir d'un sel de calcium de carbonate peu soluble au-dessus de pH 7, sous l'effet acidifiant d'une hydrolyse lente de la glucono-δ-lactone (GDL). L'intérêt d'un tel procédé reposait sur l'obtention de gels remplis à mixtes lorsque l'alginate seul ou l'alginate et la phase protéique pouvaient gélifier en présence de calcium. Des corrélations entre propriétés rhéologiques mesurées en régime dynamique (modules G' et G'') et données de microstructure ont été effectuées, par l'intermédiaire de l'analyse de texture d'image selon la méthode de cooccurrence. Chaque mélange témoignait d'une séparation de phase bloquée cinétiquement par sa gélification. Par rapport aux gels d'alginate seul ou gels remplis où l'alginate seul pouvait gélifier via le calcium, les gels mixtes témoignaient d'un effet de synergie remarquable d'un point de vue élasticité finale des gels. Dans le même temps, les globulines pré-agrégées ne montraient pas d'aptitude à la gélification selon le procédé appliqué ici. En outre, des effets ségrégatifs induisaient un enrichissement des protéines et du polyoside dans deux phases coexistantes, renforçant de ce fait des interactions entre biopolymères du même type. Les gels mixtes les plus élastiques présentaient une structure enchevêtrée avec un réseau protéique prédominant. Les observations en microscopie électronique à transmission effectuées par un marquage différentiel des deux biopolymères suggèreraient qu'il puisse se former localement des interactions attractives inter-biopolymères, probablement via le calcium, à l'interface des deux phases initialement immiscibles. Ce pontage consoliderait globalement la cohésion entre les deux réseaux protéique et polyosidique

In this thesis, several types of scaffolds composed of different materials and designed structures and functions were fabricated by 3D plotting under mild conditions (room temperature and without using any organic solvent). Broad biomaterials including inorganic (such as calcium phosphate cement and mesoporous bioglass), organic (such as alginate and gelatin) and composite materials were prepared into printable pastes to plot as 3D scaffolds for bone tissue engineering. Organic/inorganic biphasic and bipartite structure, core/shell alginate/nano-hydroxyapatite and hollow fiber structure were designed and realized. Scaffolds with multi functions including suitable mechanical properties, sustained drug/protein delivery and in vitro vascularization were achievable. 3D plotting provided great achievements in the field of tissue engineering by preparing advanced scaffolds, as well as by plotting cell/matrix constructs, and even complex tissues and organs.

La adsorció sobre carbó actiu és un tractament habitual para a l'eliminació de metalls contaminants d'afluents aquosos. Amb la finalitat de reduir el cost dels tractament actuals s'està estudiant la utilització d'adsorbents de baix cost com a substituts dels sorbents convencionals que s'utilitzen usualment en els tractaments d'aigües. En aquesta tesi s'ha avaluat la possibilitat d'aprofitar diversos residus vegetals procedents de processos agrícoles o residus industrials, com a sorbents per a l'eliminació de metalls de solucions aquoses. En concret, el treball s'ha centrat en assolir dos grans objectius, primer de tot, conèixer la possibilitat d'utilitzar el pinyol d'oliva com a adsorbent de metalls divalents de solucions aquoses, com són el Cd(II), Cu(II), Ni(II) i Pb(II), i en segon lloc, avaluar la utilització de quatre residus vegetals (escorça de yohimbe, rapa de raïm, suro i pinyol d'oliva) per a l'extracció de Cr(VI) de solucions aquoses i utilitzar el residu vegetal més apropiat com a base per tal d'obtenir un nou sorbent, amb més bona morfologia per ser utilitzat en sistemes d'eliminació de Cr(VI) en continu. Les dades cinètiques d'adsorció es van tractar amb el model cinètic de pseudo-segon ordre, amb el que es van determinar la velocitat inicial d'adsorció dels metalls. Els models d'isotermes d'equilibri de Langmuir i Freundlich es van utilitzar per descriure els equilibris d'adsorció i calcular els paràmetres de les isotermes. En els assajos amb mescles binàries de metalls, els resultats es van tractar amb el model ampliat de Langmuir.En aquest treball s'ha determinat, primerament, que el pinyol d'oliva és un bon sorbent dels metalls divalents estudiats. S'ha determinat que l'adsorció dels metalls varia amb el pH de la solució i que la presència de sals en la solució provoca una davallada en l'adsorció. També es va determinar la competència en l'adsorció entre els metalls al realitzar assajos en mescles binàries.Amb els estudis d'extracció de Cr(VI) amb els quatre materials s'ha determinat que aquests vegetals poden adsorbir el Cr(VI) en solució, tot i que la rapa i la yohimbe són els materials que presenten unes capacitats d'adsorció més elevades. Les anàlisis amb espectroscòpia electrònica de Raig-X realitzats en la rapa de raïm i la yohimbe en contacte amb Cr(VI) varen demostrar la presència del metall en els dos estats d'oxidació, Cr(VI) i Cr(III), evidenciant la participació del mecanisme de reducció de Cr(VI) en l'adsorció del metall sobre els materials.Amb l'encapsulació de la rapa de raïm es va incrementar significativament la capacitat d'adsorció del metall respecta a la seva utilització en la forma original. Les dades experimentals es van tractar amb un model de difusió i es va determinar el coeficient de difusió en l'adsorció en el sorbent amb diferent percentatge de rapa en l'interior.Finalment s'han realitzat estudis preliminars d'adsorció de crom hexavalent en continu utilitzant columnes de petites dimensions farcides amb el sorbent format per boles de rapa encapsulada en alginat càlcic. En aquests assajos s'ha determinat l'efecte en l'adsorció de metall de diversos paràmetres d'operació, com la concentració inicial de metall, el cabal i l'alçada de llit. El model de transferència de matèria i difusió en columna emprat pel tractament de les dades experimentals va mostrar l'efecte de la concentració inicial i del cabal en els coeficients de difusió i transferència de matèria. El model BDST no va predir correctament el temps de servei en els diferents paràmetres d'operació experimentats a causa de la complexitat del procés d'adsorció. Amb aquests assajos preliminars s'han establert les bases de l'adsorció de Cr(VI) amb el nou sorbent en sistemes en continu amb la finalitat de realitzar estudis posteriors d'eliminació del metall en columnes de majors dimensions. / Adsorption with activated carbon is a usual treatment to remove metals from wastewater. In order to reduce the cost of the treatment, several studies have been carried out to evaluate the use of low cost sorbents as an alternative to conventional sorbents used in wastewater treatment. In this work, the use of different vegetable wastes from agricultural or industrial processes has been evaluated as sorbents for metal removal from aqueous solutions. The aim of this work was to study first, the usefulness of olive stones as a sorbent for divalent metals such as Cd(II), Cu(II), Ni(II) and Pb(II) from aqueous solutions and then the use of four vegetable wastes (yohimbe bark, grape stalks, cork and olive stones) for the removal of Cr(VI) from aqueous solutions. The vegetable waste powder was encapsulated in calcium alginate to obtain spherical gel beads that were used in continuous flow process for Cr(VI) removal.In all sorption experiments, kinetic data were modeled by the pseudo-second order kinetic equation and determine the constants sorption rates. Langmuir and Freundlich model isotherms were use to describe sorption equilibrium data and to obtain the isotherm parameters. In binary mixtures, the extended Langmuir isotherm model was used. The results showed that olive stones are a good sorbent for studied divalent metal. Metal uptake was pH dependent and the presence of salts in solution provokes a decrease in metal uptake. A clear competence between metals to be adsorbed on the waste was observed in metal binary mixtures. Although results obtained in Cr(VI) removal studies show that the four studied wastes can adsorb Cr(VI), grape stalks and yohimbe bark wastes showed the best chromium sorption capacity. X-Ray Photoelectron Spectroscopy analysis on grape stalks and yohimbe chromium loaded samples put into evidence that both Cr(VI) and Cr(III) were sorbed on wastes surface indicating that Cr(VI) sorption process involves a redox reaction. The gel beads obtained when encapsulating grape stalks in calcium alginate showed a significant increase in Cr(VI) sorption capacity compared to the original grape stalks waste. A diffusion model was used to analyze the experimental data and to determine the diffusion coefficient for Cr(VI) sorption by beads containing different percentage of grape stalks encapsulated in calcium alginate. Finally, preliminary studies of Cr(VI) removal in continuous flow using the beads containing grape stalks powder gel in laboratory columns have been carried out. The effect of operating parameters such as feed metal concentration, flow rate and bed depth was studied. The mass transfer and diffusion model used to describe column data showed the effect of feed metal concentration and flow rate in both, diffusion and mass transfer coefficients, respectively. The bed depth service time model (BDST) failed in predicting the service time when changing operating parameters due to the complexity of the sorption process. With these preliminary column experiments we established the basis for Cr(VI) sorption by the proposed sorbent in continuous flow process for further development of the process to be used in higher scale columns.