Laboratory for Process Engineering, Environment, Biotechnology and Energy

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Publications

Symbiotic co-culture of Scenedesmus sp. and Azospirillum brasilense on N-deficient media with biomass production for biofuels

Publication . Contreras, José R.; Mata, Teresa M.; Cuellar-Bermudez, Sara P.; Caetano, Nídia S.; Chandra, Rashmi; Garcia-Perez, J. Saul; Muylaert, Koenraad; Parra-Saldivar, Roberto

The treatment of nitrogen-deficient agriculture wastewater, arising from the vegetable and fruit processing, is a significant problem that limits the efficiency of its biological treatment. This study evaluates the effectiveness of the symbiotic co-culture of Azospirillum brasilense and Scenedesmus sp., under two nitrogen levels (8.23 mg L−1 and 41.17 mg L−1) and mixing systems (aeration and magnetic stirring), aiming to simultaneously use the N-deficient media for their growth while producing biomass for biofuels. Microalgae growth and biomass composition, in terms of protein, carbohydrate and fatty acid contents, were evaluated at the end of the exponential growth phase (15 days after inoculation). Results show that the symbiotic co-culture of microalgae-bacteria can be effectively performed on nitrogen-deficient media and has the potential to enhance microalgae colony size and the fatty acid content of biomass for biofuels. The highest biomass concentration (103 ± 2 mg·L−1) was obtained under aeration, with low nitrogen concentration, in the presence of A. brasilense. In particular, aeration contributed to, on average, a higher fatty acid content (48 ± 7% dry weight (DW)) and higher colony size (164 ± 21 µm2) than mechanical stirring (with 39 ± 2% DW and 134 ± 21 µm2, respectively) because aeration contribute to better mass transfer of gases in the culture. Also, co-culturing contributed in average, to higher colony size (155 ± 21 µm2) than without A. brasilense (143 ± 21 µm2). Moreover, using nitrogen deficient wastewater as the culture media can contribute to decrease nitrogen and energy inputs. Additionally, A. brasilense is approved and already extensively used in agriculture and wastewater treatment, without known environmental or health issues, simplifying the biomass processing for the desired application.

2019Journal article

Open access

Life cycle assessment of a vanadium flow battery

Publication . Gouveia, J.; Mendes, A.; Monteiro, R.; Mata, T.M.; Caetano, Nídia; Martins, A.A.

Battery storage technologies have been showing great potential to address the vulnerability of renewable electricity generation systems. Among the various options, vanadium redox flow batteries are one of the most promising in the energy storage market. In this work, a life cycle assessment of a 5 kW vanadium redox flow battery is performed on a cradle-to-gate approach with focus on the vanadium electrolytes, since they determine the battery’s storage capacity and can be readjusted and reused indefinitely. The functional unit is 1 kWh stored by the battery. The initial results show that the environmental hotspots reside mainly in the structural and material components of the battery, evidencing the need for alternative or recycled materials, preferably produced locally. Since the quantity of electrolytes determine the amount of storable electricity, an analysis was conducted on the variation of the impacts with the increase of storage capacity. An alternative scenario with reused electrolytes was also performed. Results show that with the increase of storage capacity, the contribution of the electrolytes to the impacts decrease significantly by stored kWh. In the reused electrolytes scenario, impacts were reduced mainly for the Acidification and Mineral, fossil and renewable resource depletion categories.

2020Journal article

Open access

Flocculation of Arthrospira maxima for improved harvesting

Publication . Caetano, Nídia; Martins, A.A.; Gorgich, M.; Gutiérrez, D.M.; Ribeiro, T.J.; Mata, T.M.

The environmental impacts associated with the burning of fossil fuels coupled with growing concerns about security of energy supply, motivated the search for more sustainable forms of energy production, among which came microalgae for biofuels production. However, the commercial production of microalgae biofuels is still not competitive compared to fossil fuels, as it is necessary to solve some process bottlenecks, among which biomass harvesting, that is the focus of this work. Hence, this work intends to study the harvesting of microalga Arthrospira maxima through flocculation by pH variation and/or addition of CaCl2 as flocculant. Thus, it is described the effect of pH variation (in the range 6 to 12), followed by the addition of flocculant, on the harvesting efficiency. Results show that by pH increase over 10 using NaOH, or by flocculation using CaCl2 at a concentration of 0.2-2.0 g/L and at a 1:30 ratio (v/v) of CaCl2/microalgae culture, it is possible to effectively harvest this microalga.

2019Conference object

Open access

Life cycle assessment of a renewable energy generation system with a vanadium redox flow battery in a NZEB household

Publication . Gouveia, J.R.; Silva, E.; Mata, T.M.; Mendes, A.; Caetano, Nídia; Martins, A.A.

Buildings are responsible for a significant part of the global energy consumption. Besides the need to improve their energy efficiency, new buildings also need to generate their own energy, preferably from renewable sources, to become more sustainable. As renewable energy generation is strongly dependent on the climatic conditions, energy storage must be considered when designing such a system. In this study, a cradle-to-grave life cycle assessment (LCA) study of a renewable energy generation system with a prototype Vanadium flow battery integrated in a Near Zero Energy Building (NZEB) is performed. A combined grid-connected PV and a solar thermal system generates the energy, and it was dimensioned to supply the annual energy needs of a household in Porto, Portugal considering the local climatic conditions. As an end of life scenario, it is assumed that the battery is dismantled and most of the materials are recycled. A functional unit of 1 kWh of supplied energy to the system was considered, and study results show that environmental impacts are reduced when the energy is produced onsite and the battery components are recycled or reused. A sensitivity analysis was conducted changing the household’s geographic location.

2019Conference object

Open access

Comparison of different lipid extraction procedures applied to three microalgal species

Publication . Gorgich, M.; Mata, T.M.; Martins, A.A.; Branco-Vieira, M.; Caetano, Nídia

The increase in the world’s energy demand has contributed to the emergence of new sustainable energy sources, such as microalgae, with their great potential to provide biofuels and other high value co-products for the food and health’s markets. However, current biorefinery methodologies are either too complex to extract the targeted components such as high-value products, or require solvents with toxicity for humans and the environment. This work aims to evaluate different lipid extraction approaches applied to three microalgal species: Chlorella zofingiensis, Phaeodactylum tricornutum, and Arthrospira platensis, while employing less toxic and more economical solvents for the lipids extraction. Experimental results showed a promising outcome to tune current biorefinery methodologies, enhancing product yield as well as decreasing potential hazards.

2019Conference object

Open access