1,720,987 research outputs found
Cultivation processes to select microorganisms with high accumulation ability
No full textThe microbial ability to accumulate biomolecules is fundamental for different biotechnological applications aiming at the production of biofuels, food and bioplastics. However, high accumulation is a selective advantage only under certain stressful conditions, such as nutrient depletion, characterized by lower growth rate. Conventional bioprocesses maintain an optimal and stable environment for large part of the cultivation, that doesn't reward cells for their accumulation ability, raising the risk of selection of contaminant strains with higher growth rate, but lower accumulation of products. Here in this work the physiological responses of different microorganisms (microalgae, bacteria, yeasts) under N-starvation and energy starvation are reviewed, with the aim to furnish relevant insights exploitable to develop tailored bioprocesses to select specific strains for their higher accumulation ability. Microorganism responses to starvation are reviewed focusing on cell cycle, biomass production and variations in biochemical composition. Then, the work describes different innovative bioprocess configurations exploiting uncoupled nutrient feeding strategies (feast-famine), tailored to maintain a selective pressure to reward the strains with higher accumulation ability in mixed microbial populations. Finally, the main models developed in recent studies to describe and predict microbial growth and intracellular accumulation upon N-starvation and feast-famine conditions have been reviewed
PROCESS FOR THE CULTIVATION OF MICROALGAE FOR THE PRODUCTION OF STARCH
No full textThe invention describes a method for the cultivation of microalgae under heterotrophic and non-axenic conditions from which a particularly starch-enriched biomass is obtained, which can be extracted through an optimized method with particularly high yield
Integrated biomass production and biodegradation of olive mill wastewater by cultivation of Scenedesmus sp
No full textAbstract Biomass production and bio-treatment of olive mill wastewater (OMW) were simultaneously achieved by cultivation of Scenedesmus sp. The influence of medium composition was addressed by analyzing the effect of the addition of unsterilized OMW (9% v·v − 1 ) and of inorganic nutrients, and the use of tap water. Performance of implemented treatments was assessed by analysis of the following variables: biomass productivity, growth rate, content of target microalgal fractions (lipids and carbohydrates), and consumption of OMW organic carbon fractions (reducing sugars and phenols). The addition of unsterilized OMW (9% v·v − 1 ) caused darkening of microalgal cultures inducing transition to heterotrophic growth. Growth rate values attained in heterotrophic cultures (with OMW) (0.0181 and 0.023 h − 1 ) were comparable to those attained in autotrophic cultures (without OMW) (0.0272 and 0.0249 h − 1 ). Nonetheless, significantly lower biomass productions were achieved by heterotrophic growth (0.22 and 0.35 g·L − 1 vs. 0.56 and 0.51 g·L − 1 ). Even though leading to lower biomass productions, heterotrophic growth ensured carbohydrate productions comparable to those attained by autotrophic growth (0.1 and 0.16 vs. 0.12 and 0.17 g·L − 1 ). Biodegradation of OMW phenols was found to be significantly affected by the concentration of inorganic nutrients. The inhibition of microalgal growth induced by phenols, and the interaction between phenol biodegradation and biomass production were analyzed
Production of microalgae biomass in a continuous stirred bioreactor. Analysis of microalgae-bacteria competition mediated by nitrogen and organic carbon
No full textA model-based analysis of the competition between microalgae and bacteria mediated by nitrogen and organic carbon in a continuous bioreactor with recycle is presented. The analysis is aimed to evaluate if the ability of microalgae to uncouple nitrogen and carbon uptake can allow to prevent the contamination of bacteria with negligible carbon accumulation or to sustain the coexistence of microalgae and bacteria. To this purpose, a Droop-like model and a multiplicative Monod model are used to describe microalgae and bacteria growth kinetics, respectively. The regions of the bioreactor parameter space ensuring steady state stability of microalgae monocultures, microalgae-bacteria consortia and bacteria monocultures are identified by analytical bifurcation analysis of the mass balance equations governing bioreactor dynamics. Expressions in closed form are derived for the stability boundaries of the steady states as bioreactor parameters vary, providing guidelines for plant design and control
Effect of lipids and carbohydrates extraction on astaxanthin stability in scenedesmus sp
Full text linkElevated costs of biomass downstream processing represent a severe limit to the industrial development of microalgal production systems. Biorefinery solutions allowing simultaneously deriving biofuels and extracting high value compounds must be explored to enhance economic feasibility. In this work, the possibility to extract carbohydrates, lipids and astaxanthin from a strain of Scenedesmus sp. is investigated. The analysis is mainly focused on analyzing the effect of consolidated procedures of extraction of carbohydrates and lipids on the degradation and recovery of astaxanthin. Microalgae were cultivated till achieving stationary phase and maintained in this phase to enhance lipids and astaxanthin accumulation. The fractions of total lipids, carbohydrates and astaxanthin of the produced biomass were 17 %, 33 % and 0.02 % respectively. No statistically significant difference in the astaxanthin content determined following Soxhlet extraction and a more gentle extraction method (Yuan et al. 2002) was found. The effect of transesterification conditions was also evaluated revealing a scarce degradation of astaxanthin in response to the achievement of elevated temperature, NaOH and dissolved oxygen concentrations. Reductions in astaxanthin content were in contrast obtained in response to the addition of H2SO4. These reductions were proportional to acid sample concentration. However a regeneration of astaxanthin was obtained by NaOH addition indicating reversibility of the degradation process. In accordance with these results, the possibility to perform biomass saccharification for carbohydrate extraction at progressively lower acid concentrations was investigated. Copyright © 2015, AIDIC Servizi S.r.l
Optimization of two-phase synthesis of Fe-hydrochar for arsenic removal from drinking water: Effect of temperature and Fe concentration
Full text linkArsenic-contaminated water is a global concern that demands the development of cost-effective treatments to ensure a safe drinking water supply for people worldwide. In this paper, we report the optimization of a two-phase synthesis for producing a hydrochar core from olive pomace to serve as support for the deposition of Fe-hydroxide, which is the active component in As(V) removal. The operating conditions considered were the initial concentration of Fe in solution in the hydrothermal treatment (phase I) and the temperature of Fe precipitation (phase II). The obtained samples were characterized for their elemental composition, solid yield, mineral content (Fe and K), phenol release, As(V) sorption capacity, and sorbent stability. Correlation analysis revealed that higher Fe concentrations (26.8 g/L) ensured better carbonization during hydrothermal treatment, increased arsenic removal, reduced concentrations of phenols in the final liquid, and improved stability of the sorbent composite. On the other hand, the temperature during Fe precipitation (phase II) can be maintained at lower levels (25-80 °C) since higher temperatures yielded lower adsorption capacity. Regression analysis demonstrated the significance of the main effects of the parameters on sorption capacity and provided a model for selecting operating conditions (Fe concentration and phase II temperature) to obtain composite sorbents with tailored sorption properties
PROCESS FOR PRODUCING STARCH FROM MICROALGAE
No full textThe process described relates to the production of starch from microalgae through cultivation in an autotrophic stage followed by a subsequent heterotrophic stage. The autotrophic stage is used to produce the inoculum for cultivation under heterotrophic conditions. In the heterotrophic reactor starch accumulates in the algae. Cultivation under heterotrophic conditions is carried out with the addition of antimicrobials of natural origin of the phenol type on a growth medium such as for example one based on whey, in order to reduce contamination by bacteria and fungi. During this stage the starch content in the algae is monitored in order to maximise output. The microalgae used in the process are suitably selected for growth under the conditions reported. Oil and carotenoids are also extracted from the biomass in addition to starch. The process provides a method for the more efficient production of starch in comparison with conventional production and a method for controlling contaminants under heterotrophic growth conditions
Mechanistic modelling of copper biosorption by wild type and engineered Saccharomyces cerevisiae biomasses
No full textCopper biosorption by wild type and two engineered (Rim101 Delta, Och1 Delta) Saccharomyces cerevisiae biomasses was analyzed. Potentiometric titrations revealed that carboxylic, amino and, to less extent, phosphoric groups are responsible for the biosorption of copper. Maximum biosorption capacities of copper equal to 28.8, 8.0 and 7.5 mg/g were found at pH = 6 for wild type, Rim101 Delta and Och1 Delta respectively. A mechanistic equilibrium model was developed to describe the dependence of metal and proton binding on pH and metal liquid concentration. The developed model accounts for the exchange of metal ions with protons from functional groups in acidic form and for the sorption of metal ions on ionized groups. Model parameters were estimated based on potentiometric titration data and adsorption isotherms leading to satisfactory fitting for any considered strain. Metal removal by living cells was investigated to determine bioaccumulation capacity. No statistically significant difference was found among the bioaccumulation capacities of the three strains. For any strain, bioaccumulation could not enhance copper removal. (C) 2014 Elsevier B.V. All rights reserved
Effect of Ca2+ concentration on Scenedesmus sp. growth in heterotrophic and photoautotrophic cultivation
No full textThe influence of Ca2+ concentration on the growth of the microalga Scenedesmus sp. in heterotrophic and photoautotrophic cultivations was investigated. Heterotrophic growth was induced by the addition of olive mill wastewaters (9% v·v-1) to the culture. Variations in the calcium concentration affected differently biomass production depending on whether microalgae were cultivated under heterotrophic or photoautotrophic regime. In photoautotrophic regime, increasing the calcium concentration from 20 to 230mgL-1 decreased maximum cell concentration and growth rate. In heterotrophic cultivation, cell concentration and growth rate decreased with Ca2+ concentration increasing from 20 to 80mgL-1 but then increased with Ca2+ concentration increasing to 230mgL-1. Increasing calcium concentration invariably promoted cell aggregation. The precipitation of calcium phosphates can explain the decreasing growth rate and cell concentration attained with increasing calcium concentration, while the influence of Ca2+ concentration on the adsorption of phenols on suspended solids can explain the enhanced growth attained at large Ca2+ concentration under heterotrophic regime. Implications of the illustrated results for industrial scale application of microalgae are thoroughly discussed. © 2017 Elsevier B.V
Lanthanum biosorption by different Saccharomyces cerevisiae strains
Full text linkBiosorption can be a promising technology in rare earth metal separation and recovery due to the low costs of waste biomasses (used as biosorbents) and the high selectivity exploiting specific interaction between metals and biological active sites. In this work, Saccharomyces cerevisiae biomass was used to recover lanthanum. Biosorption properties of two S. cerevisiae strains, wild type and rim20. mutant, have been tested. Potentiometric titrations were carried out for rim20. mutant strain and compared with wild type. Nature of the main active sites and their concentration were determined by implementing mechanistic models. Carboxylic, amino and phosphoric sites are the main groups present. Higher concentration of negatively charged sites was found in rim20. (0.0024 mol/g) than in wild type (0.0022 mol/g). The rate of lanthanum biosorption process is very fast requiring only 10-20 minutes to reach equilibrium condition for both strains. Then biosorption equilibrium tests were done for both biomasses by testing two equilibrium pH (4.0 and 6.0). Maximum uptake capacities (qmax) were: 70 mg/g and 40 mg/g at pH 4.0 for rim20. and wild type, respectively, and 67 mg/g and 80 mg/g at pH 6.0 for wild type and rim20., respectively. These data evidenced that: rim20. mutant had a higher maximum biosorption capacity with respect to wild type counterpart, and that pH had a relevant effect on lanthanum removal. S. cerevisiae yeast denoted good lanthanum biosorption properties and, between tested strains, rim20. was found to be the most promising for such aim
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