1,721,058 research outputs found
Gas-liquid mass transfer rates in unbaffled tanks stirred by PBT: scale-up effects and pumping direction
No full textUnbaffled stirred tanks are increasingly recognized as a viable alternative to common baffled tanks for a range of applications such as biochemical, food or pharmaceutical processes where the presence of baffles is undesirable for some reason. In this work, the mass transfer performance of unbaffled stirred tanks with pitched blade turbine, operating either in up-pumping or down-pumping mode, was investigated. The influence of impeller size and liquid viscosity were also investigated. The mass transfer intensity was measured by means of the Simplified Dynamic Pressure. Method: The measurements concerned both coalescent and non-coalescent (viscous) batches. Results: confirm that increasing apparatus size has a slightly positive effect on gas-liquid mass transfer coefficient. It was also found that when the PBT is operating in the up-pumping mode the formation of surface oscillations, which lead to undesired instabilities of the whole apparatus, is conveniently minimized. In the super-critical regime, the unbaffled tanks provide a performance comparable with that of the standard (baffled) bioreactors at the same power dissipation, which makes them a viable alternative for general fermentation operations and other gas–liquid reactions
Growing microalgae in a “quasi-isoactinic” photobioreactor
Full text linkThe aim of this work is setting up the conditions of an “iso-actinic” photobioreactor that is a photoreactor for the cultivation of microalgae in which the local volumetric rate of photon absorption (LVRPA), can be considered uniform to a good extent. We describe the composition of this cheap photoreactor and how we made it. The system is driven by an Arduino platform that makes it possible to control light intensity as well as light-dark cycles. Preliminary results obtained by growing Nannochloropsis gaditana, a microalga famous for its fat content, in this innovative reactor are presented. We finally observed how microalgae responds to flashing light irradiation
Utilization of native Chlorella strain in laboratory-scale raceway reactor for synthetic wastewater treatment: A study in batch and continuous modes with multi-substrate modeling
Full text linkDespite of the possibility to include microalgae in civil wastewater treatment process, the practice is still not common due to the lack of available instruments to implement it. In this study, a straightforward comprehensive approach for dealing with microalgal wastewater treatment involving an original kinetic model is proposed. A first set of batch cultures of a native strain of Chlorella was firstly carried out to obtain the kinetic parameters: maximum growth factor (μmax) and half-saturation constant (Ks), for each limiting nutrient. Maximum growth factor values of 0.0279 for PO43−, 0.0319 h−1 for NH4+, 0.0352 h−1 for glucose, and 0.0263 h−1 for the overall medium were found. Regarding the Ks, values of 1.08 mg L−1, 27.70 mg L−1, 1.34 mg L−1, were found for PO43−, NH4+ and glucose respectively, and a value of 2.8 % of the total nutrients for the overall medium. These parameters were used to set a multi-substrate kinetic model able to predict the growth in batch and in continuous operation within a laboratory scale raceway reactor. The removal capabilities of the microalgae for each addressed pollutant were evaluated in a batch system and in a continuous system at dilution rates of 0.0025, 0.005, 0.01 and 0.015 h−1. This comprehensive approach represents a significant step towards addressing the continuous treatment of wastewater utilizing microalga
Microalgae in the Mediterranean area: A geographical survey outlining the diversity and technological potential
Full text linkMicroalgal diversity enables the possibility to employ them in technological applications, as widely shown by the
modern literature. While there exists an extensive body of literature concerning the technological applications of
microalgae, the scientific knowledge of microalgal species remains relatively limited. Therefore, there is still
potential for unlocking new opportunities through the study of the microalgal biodiversity, particularly in the
Mediterranean region, which is unique because of its sub regional diversity. While some studies have assessed
microalgae distribution in the Mediterranean area, and others have focused on specific aspects of their technical
exploitation, this review seeks to offer a comprehensive overview of isolated microalgal species and their
technological applications. Microalgae from the Mediterranean area share common characteristics, such as low
half-saturation constants and acclimation to high light intensity, making them ideal for specific technological
applications. While the search for new microalgae for technological purposes can help in biodiversity conservation, numerous species still remain underexplored, offering potential for innovative applications. However, the
key finding from the critical analysis of the literature is that the diversity of microalgae in the Mediterranean
region is its true richness, allowing for their versatile applications across various processes. The work focuses on
the Mediterranean area, i.e., having coastlines along the Mediterranean Sea and on aquatic microalgae, coming
from water with different salinity levels. This review offers an intrinsic ecological and technological perspective
and provides a fresh outlook on the microalgal sector, promoting its expansion in the Mediterranean area and the
development of sustainable bio-industrie
Syngas production from organic fraction of municipal solid waste by supercritical water gasification
No full textInoculum of indigenous microalgae/activated sludge for optimal treatment of municipal wastewaters and biochemical composition of residual biomass for potential applications
Full text linkIn this work, municipal wastewater was treated with microalgal/activated sludge consortia. We aimed at
obtaining a positive interaction between the microalgae and the heterotrophic bacteria and identifying the best
combination for bioremediation purposes. A strain of Chlorella sp CW2 employed in this work was isolated from
AS and molecularly characterised in this work for the first time. This strain and another previously isolated strain
(Chlorella sp Pozzillo) were inoculated alone and in combination with AS in different ratios in wastewaters.
Microalgae/activated sludge growth curves were obtained by using a UV–vis spectrophotometer and a fluorimeter
to distinguish the contribution of the photosynthetic microorganisms to the total growth. The effectiveness
for the bioremediation of municipal wastewaters was evaluated by measuring the COD, the total
nitrogen and total phosphorous content at the end of batch cultivations. Overall, the best abatement was achieved
by the microalga Chlorella sp CW2 inoculated with activated sludge in the ratios 1:2 and 2:1, with a
decrease of 81.39 % ± 0.56, 86.12 % ± 0.43, 82.89 % ± 2.66 and 82.5 % ± 0.83, 72.66 % ± 0,46, 97.15 % ±
0.44 of COD, total nitrogen and total phosphorous, respectively. Finally, the residual biomass, constituted by a
sludge enriched in microalgae, was analysed for its content in carbohydrates, lipids and fatty acid in order to
suggest the best application for its valorisation. Considering the final composition of the obtained biomass and its
remediation potential, the most promising sample may be the microalga Chlorella sp CW2 inoculated with
activated sludge in the ratio 1:5
Lutein Production and Extraction from Microalgae: Recent Insights and Bioactive Potential
Full text linkMicroalgae have been reported to be excellent producers of bioactive molecules. Lutein is a pigment reported to have various beneficial effects for humans, and especially for eye well-being. In the current review, we summarize various methods that have been developed to optimize its extraction and bioactivities reported for human health. Several protective effects have been reported for lutein, including antioxidant, anticancer, anti-inflammatory, and cardioprotective activity. This review also reports attempts to increase lutein production by microalgae by changing culturing parameters or by using pilot-scale systems. Genetic engineering lutein production is also discussed. Considering the increasing aging of the worldwide population will create an increased need for lutein, a viable economic and eco-sustainable method to produce lutein is needed to face this market demand
Experimental and Computational Study of Supercritical Fluid Extraction (SFE) of Omega-3 Components from Fish Oil in Structured Packing
Full text linkThe benefits of polyunsaturated fatty acids and their implications for human health have gained scientific
attention to their extraction from biological sources, not being produced by the human body. Most known
industrial productions of omega-3 fatty acids often work under operating conditions that may degrade these
components and they often use toxic or flammable solvents that can adversely affect human health. In this
sense, innovative and interesting prospects are provided by Supercritical Fluid Extraction (SFE).
In this work, two parallel studies were carried out: an experimental activity in a laboratory apparatus using
supercritical carbon dioxide (scCO2) and preliminary computational fluid dynamics (CFD) simulations, limited to
the hydrodynamic aspects of the process. In the experimental apparatus a Sulzer® EX structured packing, made
up of corrugated metal gauze sheets, was used as the column filler. The study made it possible to identify the
optimal operating conditions leading to an enrichment of the starting mixture in Eicosapentaenoic acid (EPA)
and Docosahexaenoic acid (DHA), target products. CFD simulations were based on the Volume of Fluid (VOF)
approach, suitable to the present complex multiphase system with two phases in close contact (transesterified
fish oil and scCO2). The meatus created by the corrugations of the metal gauze was chosen as the calculation
domain representative of the system. The computations were performed by the commercial software Ansys
Fluent®, which allowed the prediction of the hydrodynamic evolution of the system through transient simulations.
CFD predictions were in qualitative agreement with the experimental result
Kinetic of the Sewage Treatment: The Consumption of Organic Carbon of The Microalga Chlorella sp
Full text linkAs well known, microalgae are eukaryotic or procaryotic microorganisms able to photosynthesize, namely
transforming inorganic substrates and sun light into organic compounds and chemical energy. They result very
promising in treating civil wastewaters thanks to their ability to employ nitrates and phosphates as nutrients
(Lima et al., 2019). Autotrophic microalgae are, anyway, not useful in decreasing the organic carbon content of
wastewaters, and for this reason, they cooperate with heterotrophic bacteria. The usefulness of microalgaebacteria consortia in treating wastewaters and the ratio of their inoculum was investigated in a previous work
(Lima, 2022a). Contrarily to autotrophic microalgae, mixotrophic microalgae are able to decrease the organic
content of the matrix in which they are grown. In this work, we preliminarily investigated the capability of the
autochthonous microalga Chlorella sp. CW2 to grow in mixotrophy and decrease the organic content of the
artificial wastewater in which they are grown. Several batch cultivations were performed with glucose in different
concentrations. Kinetic parameters were obtained and employed to determine the dilution rate (D) ideal for the
abatement of glucose from the artificial wastewater
MODELLING OF THE GROWTH OF NANNOCHLOROPSIS GADITANA IN DIFFERENT REACTOR GEOMETRIES, EXPERIMENTAL KINETIC PARAMETERS FROM BATCH CULTURES AND BIOCHEMICAL ANALYSIS OF THE OBTAINED BIOMASS
No full textMicroalgae are unicellular and photosynthetic microorganisms that grow using inorganic salts, CO2 and light, and are applied in numerous industrial sectors due to their variety and properties. Due to the lack of information on how microalgae respond to external inputs and to the different environments in which they grow, today the industrial application is not exploited as it should.
It is therefore necessary to create models that allow to predict microalgal growth in different photobioreactors to improve our knowledge, still poorly investigated.
In this work the Monod equation for the specific growth rate was combined with the Lambert-Beer law for the non-homogeneous light distribution in a flat photobioreactor.
Model kinetic parameters related to the cultivation of the microalga Nannochloropsis gaditana were obtained from batch cultivations under different photon-flux densities inside a quasi isoactinic photobioreactor. These parameters were applied in a mathematical model, based on the geometric system considered, for obtaining microalgae growth curves.
Biochemical analyses on the obtained biomass were also executed at the end of each batch cultivation to assess how light distribution influences biomass composition.
The obtained model allowed to successfully predict the growth of the microalga Nannochloropsis gaditana in the different photobioreactor geometries
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