Reuse of Water and Nutrients in Soilless Plant Culture

This dissertation proposes two approaches to mitigating the dependency of soilless culture on scarce mineral fertilisers. The first approach aims to increase the lifetime of the NS used in recirculating hydroponic systems, while the second approach presents a holistic method for the treatment and use of aquacultural sludge as NS for soilless growth systems. This method includes two steps: nutrient mobilisation using aerobic digestion (AD), followed by solids precipitation using the biopolymer chitosan as the flocculant. The recovered NS was used to grow lettuce in a recirculating hydroponic system. The outcome of the first approach showed that NS can be used for several weeks before discharge, even though many growers discard recycling NS at weekly intervals. In this study, NS was reused for 6 weeks, corresponding to a production of 1 kg lettuce per 10 litres tank volume of NS, in a closed hydroponic system without compromising the yield and apparent quality of lettuce. The results from the second approach indicated that AD is an efficient method to mobilise nutrients in aquacultural waste to concentrations close to or exceeding the mineral levels recommended for soilless growth systems. In addition, the biopolymer chitosan proved to be an efficient and safe alternative for solids removal from aerobically digested aquacultural waste. The recovered NS was successfully used for lettuce production in a closed hydroponic system, with yield and quality comparable to those of lettuce grown with conventional NS. The results obtained clearly show the possibility of substituting synthetic fertilisers with recovered NS from aquaculture waste, which can be considered an alternative and resource-efficient fertilisation strategy for soilless culture systems. Both approaches are described in this dissertation, while detailed explanations of the materials and methods used, as well as the obtained results, can be found in the appended papers.publishedVersio

Quality and yield of lettuce in an open-air rooftop hydroponic system

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Dual-aptasensor array for osteopontin detection: optimization of aptamers immobilization conditions

Mestrado com dupla diplomação com o High Institute of Biotechnology of Monastir (ISBM), TunisiaCancer diseases are associated with the presence of several protein biomarkers. Aptasensor arrays may allow early multiple-detection of these biomarkers which can make significant improvements in the lives of cancer patients. Clinical studies suggest that osteopontin, an overexpressed protein by tumor cells, may be used as a diagnostic biomarker for various cancers. The aim of the present work was to establish the optimal experimental conditions that allow enhancing the performance of an electrochemical dual-aptasensor array for the detection of osteopontin. The aptamer concentration, time and temperature of immobilization into the dual-screen printed gold electrodes (Dual-SPGE) as well as the aptamer-protein interaction time were evaluated using a 2k factorial experimental design. DNA and/or RNA aptamers were immobilized on the Dual-SPGE via streptavidin-biotin interaction and the evaluation of the best experimental conditions was carried out by cyclic and square wave voltammetry using a ferro/ferricyanide solution ([Fe(CN)6]3−/4−) as a redox probe. Statistical significant models for both DNA and RNA aptamers were established. Temperature and aptamer concentration were found to be the most significant parameters. Also, the results pointed out that interaction effects between the four parameters were usually statistically significant, showing that there was a dependency between aptamer concentration-aptamer immobilization time and between temperature-aptamer immobilization time. The optimum experimental conditions found for enhancing the performance of the dual-aptasensor array were 4°C, 0.5 μM of aptamer concentration, 20 min of aptamer incubation and 30 min of aptamer-osteopontin interaction.O cancro é uma doença à qual pode ser associada a presença de diversas proteínas nos fluidos biológicos de pacientes com essa patologia, as quais podem ser usadas como biomarcadores. Os biossensores à base de vários aptâmeros (aptasensors arrays) podem permitir a deteção múltipla desses biomarcadores num estágio precoce da doença, podendo proporcionar melhorias significativas na vida dos pacientes com cancro. Estudos clínicos sugerem que a osteopontina, é uma proteína sobre-expressa por células tumorais, podendo ser utilizada como biomarcador no diagnóstico de vários tipos de cancro. O objetivo do presente trabalho foi estabelecer as condições experimentais que maximizassem o desempenho de um duplo biossensor eletroquímico contendo dois aptâmeros (duplo-aptasensor array) para a deteção de osteopontina. O desenho experimental 2k fatorial foi utilizado com o intuito de estudar o efeito da concentração dos aptâmeros, tempo e a temperatura de imobilização no elétrodo de trabalho de ouro duplo (duplo-SPGE), bem como o tempo de interação aptâmero-proteína. Os aptâmeros de ADN e/ou ARN foram imobilizados no duplo-SPGE através da interação biotina-estreptavidina e a avaliação das melhores condições experimentais foi realizada por voltametria cíclica e voltametria de onda quadrada usando uma solução de ferro/ferricianeto ([Fe (CN)6]3-/4-) como solução redox. Para os aptâmeros de ADN e ARN foram estabelecidos modelos significativos, sendo a temperatura e a concentração dos aptâmeros os parâmetros mais significativos. Além disso, os resultados mostraram que o efeito da interação dos 4 parâmetros foi em geral estatisticamente não significativo, verificando-se uma dependência do tempo de imobilização dos aptâmeros com a concentração dos aptâmeros e com a temperatura aplicada, respetivamente. As condições experimentais ótimas estabelecidas de forma a melhorar o desempenho do duplo-aptasensor array foram uma temperatura de 4ºC, com uma concentração de 0.5 μM para dois aptâmeros, após 20 min e 30 min de incubação no duplo-SPGE e de interação aptâmeros-osteopontina, respetivamente.Les maladies cancéreuses sont liées à plusieurs biomarqueurs protéiques qui peuvent être précocement détectés par des biocapteurs à aptamères et par conséquent des améliorations notables peuvent être apportées à la vie des patients. Des études cliniques suggèrent que l'ostéopontine, une protéine surexprimée par les cellules tumorales, peut être utilisée comme un biomarqueur pour le diagnostic du cancer. Le but du présent travail est d'établir les conditions expérimentales optimales permettant d'améliorer la performance d’un biocapteur éléctrochimique à deux aptamères pour la détection de la protéine ostéopontine. La concentration de l'aptamère, la température et le temps d’immobilization de l’aptamère sur une électrode en or imprimée par sérigraphie ainsi que le temps d'interaction aptamère-protéine ont été évalués en suivant un plan factoriel à deux niveaux. Les aptamères ont été immobilisés sur l’électrode via une interaction streptavidine-biotine et l'évaluation des meilleures conditions expérimentales a été effectuée par voltammetrie cyclique et par voltampérométrie à impulsion rectangulaire en utilisant une solution de ferro/ferricyanure ([Fe(CN)6]3-/4-) comme sonde redox. Des modèles statistiquement significatifs relatifs aux aptamères d'ADN et d'ARN ont été établis. La température et la concentration de l'aptamère ont été les paramètres les plus significatifs. L'effet des interactions entre les quatre paramètres a montré qu'il existe une dépendance entre la concentration de l'aptamère et le temps d'immobilisation de l'aptamère et entre la température et le temps d'immobilisation de l'aptamère. Les conditions expérimentales optimales pour améliorer la performance du biocapteur étaient 20 minutes d'incubation d'aptamère, 30 minutes d'interaction aptamère-ostéopontin, une température d’incubation de 4°C et une concentration d'aptamère de l’ordre de 0,5 μM

Quality and Yield of Lettuce in an Open-Air Rooftop Hydroponic System

In this study, the yield and growth performance of lettuce in an open-air rooftop hydroponic system were investigated. Lettuce was grown in a closed recirculating nutrient film technique (NFT) unit using a standard nutrient solution (NS). Yield, fresh weight, and nutrient content in the leaf tissue of the harvested lettuce were measured. The results were compared with the results obtained in indoor hydroponic lettuce growth with artificial lightning. Despite strong winds during the growth period, 25% of the total lettuce heads weighed twice the marketable weight; however, 25% of the total lettuce heads were below the marketable weight. A more efficient nutrient uptake was indicated by the lettuces in the rooftop system compared with the uptake in the indoor system. Foliar analysis revealed a higher content of all nutrients in the leaves of rooftop hydroponic lettuce compared with indoor hydroponic lettuce. This study suggests that hydroponic rooftop-grown lettuce can be competitive with their indoor counterparts if the rooftop hydroponic system is protected from extreme weather conditions

Quality and yield of lettuce in an open-air rooftop hydroponic system

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Hydroponic lettuce cultivation using organic nutrient solution from aerobic digested aquacultural sludge

The aim of this study was to demonstrate how aquacultural sludge can be processed and utilized as an organic nutrient solution (ONS) for hydroponic lettuce production. By using a previous developed method, approximately 80% of the processed sludge was reclaimed as a clear, nutrient-rich solution. The performance of the recovered nutrient solution on lettuce growth was assessed in a nutrient film hydroponic system. The results were compared to the results obtained using a conventional nutrient solution (CNS). Yield, fresh weight, water consumption, and nutrient and heavy metal content in leaf tissue were measured. In spite of a 16% lower average fresh weight obtained in ONS compared to the weight obtained in CNS, there was no statistical difference of the yield of lettuce among the two nutrient solutions. After the cultivation period, 90% of the lettuce heads grown in ONS exceeded the marked weight of 150 g. Foliar analysis revealed a similar or higher content of all nutrients, except of magnesium and molybdenum in the leaves of lettuce grown in the ONS compared to lettuce grown in the CNS. This study shows that nutrients recovered from aquacultural sludge can be utilized as fertilizer, thereby reducing the dependency on mineral fertilizer in hydroponic and aquaponic systems