Efeito de pré-tratamentos térmicos, à pressão atmosférica, na digestão anaeróbia mesófila e termófila de resíduos de casca de batata

Dissertação para obtenção do Grau de Mestre em Energia e BioenergiaOs resíduos de batata que são produzidos em indústrias alimentares são constituídos por matéria orgânica, mas esta não está totalmente disponível para sofrer biodegradação por via anaeróbia, devido à complexidade das substâncias que a constituem. Os pré-tratamentos térmicos podem permitir o aumento da biodegradabilidade desses resíduos. A presente dissertação teve como principal objetivo o estudo do efeito de pré-tratamentos térmicos na eficiência do processo de digestão anaeróbia (DA) mesófila e termófila de um resíduo de casca de batata, em particular, nos rendimentos de produção de biogás e metano. O resíduo de casca de batata foi previamente triturado em todos os ensaios, até uma dimensão inferior a 2 mm. Num dos ensaios não foi aplicado qualquer pré-tratamento térmico (controlo). Nos restantes três ensaios, as amostras foram submetidas a um pré-tratamento térmico de cozedura num banho de água termostatizado, a 70ºC, com diferentes tempos de aquecimento: 1,5 h, 3,0 h e 6,0 h. Os ensaios nos quais os resíduos pré-tratados foram introduzidos no digestor mesófilo (37±2°C), do tipo UASB, foram designados por EM37/70-1.5, EM37/70-3 e EM37/70-6. Os ensaios nos quais os resíduos pré-tratados foram introduzidos no digestor termófilo (50±3°C), do tipo CSTR, designaram-se por ET50/70-1.5, ET50/70-3 e ET50/70-6. Para o regime mesófilo, os ensaios EM37/70-3 e EM37/70-1.5 foram os que apresentaram os resultados mais elevados dos rendimentos de produção de metano, com 396 cm3.g-1 SV removidos e com 313 cm3.g-1 CQO total removida, respetivamente. Na gama termófila, o ensaio ET50/70-3 foi o que apresentou os rendimentos de produção de CH4 mais elevados, com 368 cm3.g-1 SV removidos e com 337 cm3.g-1 CQO total removida. De uma forma geral e tendo apenas em consideração os dados experimentais obtidos na presente dissertação, o pré-aquecimento a 70ºC, durante 3 h, revelou-se como o mais eficaz, quer no digestor mesófilo, quer no digestor termófilo

Benefits and drawbacks of energetic valorisation of Eucalyptus Globulus stumps by thermochemical processes

n the pulp and paper industry in Iberian Peninsula there is an intensive use of eucalyptus globulus that has a fast growth and a high productivity. There are large areas of forest dedicated to its growth. After 9 to 12 year rotation cycles trees are cut and the stumps are left in the fields. After 2 or 3 harvesting cycles these tree stumps are removed from the fields and considered low value biomass wastes. This corresponds to depletion on organic matter and of valuable minerals related to soil fertility. The use of these biomass wastes in thermochemical conversion processes like gasification or combustion may be a valuable alternative solution as it allows taking profit of these wastes energetic content. The solid by-products obtained by thermal conversion (ashes) may be incorporated in soils to return the valuable minerals and to ensure a good forest management system. Stumps removed from eucalyptus stands were used in combustion trials to improve the burning conditions and in gasification tests with different experimental conditions to obtain syngas suitable to be used in furnaces (chemical recover) of pulp industries. Stumps combustion and gasification processes were compared in terms of stumps energetic valorisation, gaseous emissions and gasification gas utilisation.

Comparison of co-gasification of wastes mixtures obtained from rice production wastes using air or oxygen

The world annual production of rice is higher than 700.7 million tons, which generates rice husk and straw wastes. Rice culture also produces big amounts of polyethylene (PE) bags used in rice packs and for seeds and fertilizer storage that usually end up in landfills, due to their degree of contamination. The energetic valorisation of these wastes may be accomplished by different processes, co-gasification is one of the most viable, as it leads to the production of a synthetic gaseous mixture (bio-syngas) that can be used for energy production to be used during rice milling processes. Gasification of rice husks has some challenges, due to these wastes high content of silica and alkali metals that lead to the formation of solids with lower melting point, thus, leading to bed agglomeration that causes reactor erosion and serious damage. PE has lower ash content and much higher energetic content than rice husks. However, PE polymeric structure may lead to the formation of higher tar contents, which compromise most gasification gas utilisations. Co-gasification of PE and rice husks allows taking advantages of each waste favourable characteristic, diluting the unsuitable features. Co-gasification of these wastes was done in presence of steam blended with air or oxygen. Steam promoted the gasification reactions and favoured H2 production. Air or oxygen promoted the partial oxidation of the feedstocks to be co-gasified and supplied the energy necessary for the endothermic gasification reactions. The use of air has a low cost, but has the great disadvantage of diluting the bio-syngas produced, thus lowering its energetic content. On the other hand, the use of oxygen solves the problems related to gas dilution with nitrogen, but increases the operating cost. Bio-syngas composition obtained by co-gasification trials done with air enriched with different oxygen contents was compared with those obtained with air or pure oxygen to determine the best approach considering both the technical and economical sustainability

Random mutagenesis as a promising tool for microalgal strain improvement towards industrial production

Microalgae have become a promising novel and sustainable feedstock for meeting the rising demand for food and feed. However, microalgae-based products are currently hindered by high production costs. One major reason for this is that commonly cultivated wildtype strains do not possess the robustness and productivity required for successful industrial production. Several strain improvement technologies have been developed towards creating more stress tolerant and productive strains. While classical methods of forward genetics have been extensively used to determine gene function of randomly generated mutants, reverse genetics has been explored to generate specific mutations and target phenotypes. Site-directed mutagenesis can be accomplished by employing different gene editing tools, which enable the generation of tailor-made genotypes. Nevertheless, strategies promoting the selection of randomly generated mutants avoid the introduction of foreign genetic material. In this paper, we review different microalgal strain improvement approaches and their applications, with a primary focus on random mutagenesis. Current challenges hampering strain improvement, selection, and commercialization will be discussed. The combination of these approaches with high-throughput technologies, such as fluorescence-activated cell sorting, as tools to select the most promising mutants, will also be discussed.info:eu-repo/semantics/publishedVersio

Effects of LED lighting on Nannochloropsis oceanica grown in outdoor raceway ponds

Growth in most microalgal mass cultivation systems is light-limited, particularly in raceway ponds (RWP) where the light path is higher. Artificial lighting can be a promising solution to diminishing dark zones and enhance microalgal productivity. Therefore, our goal was to prevent the cell shift from photosynthesis to a respiration-only stage by resorting to LED illumination. Nannochloropsis oceanica cultures were accordingly grown out-doors in a preliminary small-scaleexperiment, followed by pilot-scale trials. In the former, three 3.0-m(2) RWP were set up under three distinct conditions: 1) without LEDs (control); 2) LEDs turned on during the night; and 3) LEDs turned on for 24 h. In the pilot-scale trial, one of two 28.9-m(2) pilot-scale RWPs was coupled to the best LED setup - determined in the small-scale preliminary experiment - using the same light intensity (normal mode) and half of the intensity (economy mode), with the second RWP serving as a control. In the preliminary experiment, the use of LEDs for 24 h was deemed as not helpful during daytime, before the culture reached asymptotic to 0.5 g DW L-1 - when dark zones appeared during the day due to sunlight attenuation in the 0.1 m-deep cultures. Overall, use of LEDs increased biomass growth chiefly by increasing nighttime productivities - materialized in higher chlorophyll, protein, and carbohydrate productivities in LED-lit cultures. A higher impact of LED lighting was observed under lower sunlight irradiances. A preliminary economic analysis indicates that use of LEDs in RWPs outdoors should be considered for high-value metabolites only.info:eu-repo/semantics/publishedVersio

Improving bio-oil furans yields by thermo-catalytic reforming process investigating different feedstocks and catalysts

Lignocellulosic biomass is known as a second-generation biomass which means it is non-food competing. It is the most abundant renewable resource existing, and presently it is considered as a promising feedstock for the synthesis of green chemicals and biofuels for reducing transportation emissions and dependence on fossil fuels. Steel slag are by products of the steel industry, which are composed of various metal oxides promoting a catalytic effect on pyrolysis products improving their quality. It is a cheap and sustainable alternative to replace zeolites, the most common cracking catalysts. In this research, a TCR (Thermo-Catalytic Reforming) reactor and steel slag are used to transform lignocellulosic biomass into high quality bio-oils. TCR is a combination of intermediate pyrolysis followed by a second post reforming step. Intermediate pyrolysis heats biomass to moderate temperatures between 400–500°C in the absence of oxygen, with a short vapour residence time (seconds) and moderate solid residence time (minutes). Post reforming is achieved at temperatures between 500-800°C with extended vapour and char residence times. One characteristic of the process is that the final products (bio-oil, syngas and biochar) contains a higher energy density than the original feedstock (superior than other pyrolysis technologies) having the advantage to be easily transported and stored. Oat hulls and sugarcane bagasse were processed in the TCR working with temperatures between 400-500 ºC in the intermediate pyrolysis reactor and 500-700 ºC in the reforming unit. Steel slag were applied in the system in two different ways: 1) mixed with the biochar in the reforming unit at different mass ratios (30, 70 and 100 wt% of steel slag); 2) mixed with the feed and introduced in the intermediate pyrolysis reactor at different mass ratios (10, 20 and 30 wt% of steel slag). The introduction of steel slag in the TCR reactor increased the H$_2$ yield by 80.0% and consequently the HHV by 12.3% for the syngas. The steel slag also upgraded the biooil by reducing the viscosity, water content and acid number by 46.6, 55.1 and 65.7% respectively. Moreover, the HHV of the same bio-oil raised 22.0%. All these improvements make the pyrolysis oil more attractive and suitable to be used as a biofuel. In terms of furfural and furans, the best results (2.8 and 9.8%, respectively) were achieved by introducing 100 wt% of steel slag in the reformer and using sugarcane bagasse as a feedstock

Mass balance analysis of carbon and nitrogen in industrial scale mixotrophic microalgae cultures

Large-scale cultivation of Chlorella vulgaris is of great interest given the extent of products and potential applications that can derive from its biomass. From an industrial point of view it is imperative to consistently obtain highproductivities and high quality biomass at the lowest production costs. The mass balance of critical nutrients suchas carbon and nitrogen is therefore necessary to quantify its recovery and consumption yields, the efficiency ofthe biomass production system and to identify operational optimization opportunities.The mass balance of C. vulgaris mixotrophic growth throughout scale-up from 10 m3 to 100 m3 on acetate andurea as carbon and nitrogen sources was calculated using a black-box model developed to illustrate the inputsand outputs of the system in quasi-real time and resulted on recovery factors of 0.99 ± 0.08 and 0.99 ± 0.25, respectively. Under these conditions C. vulgaris cultivation yielded a maximal productivity of 0.14 g L−1 d−1 andmaximal growth rate of 0.38 d−1. Both parameters decreased throughout scale up reaching an average productivity of 0.09 g L−1 d−1 with an average growth rate of 0.13 d−1 for the whole process. Global carbon and nitrogenyields measured were 0.76 molC-X molC−1 and 0.72 molN-X molN−1. The mass balance determination indicates theincorporation of both acetate and urea carbon atoms into the biomass. Therefore, external inorganic carbon fromCO2 was concluded to have little influence on microalgae growth in the conditions studied apart from pH control.Urea and ammonium were found to be effectively used by C. vulgaris cells. However, despite the satisfactory yieldobtained for nitrogen, the metabolism of urea resulted in ammonium build-up in the culture medium.To our knowledge this is the first report of growth parameters and mass balance analysis of a Chlorella sp. culturein industrial scale closed tubular photobioreactors