Hydrogen photo-production by mixotrophic cultivation of chlamydomonas reinhardtii: Interaction between organic carbon and nitrogen

Hydrogen photo-production by a wild type and two engineered strains of Chlamydomonas reinhardtii was investigated. Growth rate values and hydrogen yields attained as the concentration of acetate and nitrogen vary were compared. In the analysis of microalgal growth, the interaction between organic carbon (acetate) and nitrogen (nitrate) was investigated by recourse to an experimental factorial design. This analysis evidenced the existence of a statistically significant interaction between organic carbon and nitrate. Hydrogen production was attained by cultivating microalgae previously grown in mixotrophic regime with sulphur deprived medium. The influence of varying the photobioreactor headspace on hydrogen production was investigated. This analysis revealed an increase in the hydrogen produced per unit volume of culture of about one order of magnitude when the headspace volume is modified from 100 to 350 mL. This result provides valuable indications on how to design and operate photobioreactors for hydrogen production optimization and was thoroughly discussed in terms of the metabolic pathways activated by sulphur depletion. ©2014, AIDIC Servizi S.r.l

Lanthanum biosorption by different Saccharomyces cerevisiae strains

Biosorption 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

Effect of lipids and carbohydrates extraction on astaxanthin stability in scenedesmus sp

Elevated 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

Two stage process of microalgae cultivation for starch and carotenoid production

Biotechnological processes based on microalgae cultivation are promising for several industrial applications. Microalgae are photoautotrophic microorganisms and can thus grow by using renewable and inexpensive resources as sunlight, inorganic salts, water and CO2. They can store high amounts of neutral lipids (bioil), carbohydrates (mainly starch), carotenoids (such as lutein, astaxanthin, beta-carotene), proteins and other molecules. Productions of lipids and carbohydrates have recently received an increasing interest for biofuel production, while proteins, carotenoids and other minor products are usable as feed additives and nutraceutical compounds. Biofuel production from microalgae is not yet economically sustainable, while there are different industrial plants in the world for the production of high values chemicals as carotenoids. Starch production from microalgae has been investigated mainly for the production of biofuels (e.g. bioethanol) by successive fermentation. However, purified starch can be used for other aims such as the production of bioplastics. Superior plants as corn, potato and wheat are currently used for this purpose. However, there are different environmental and economic issues related to the use of fertile lands and edible plants for these kinds of productions. Microalgae can solve these social and ethical issues because they can grow on nonfertile lands and also reach starch productivity per hectare higher than plants. In this work, the production of starch and carotenoids from Scenedesmus sp. microalgal strain is reported. A two-stage process has been developed in order to reduce operative and investment costs. In the first stage, microalgae are cultivated in photoautotrophic conditions and then, when biomass concentration rises and light becomes a limiting factor for growth, microalgae are transferred to a heterotrophic reactor. In this reactor, microalgae are cultivated by using wastewaters as source of nutrients (mainly organic carbon). Microalgae use organic carbon to synthesize starch and simultaneously reduce the content of pollutants in the wastewater (codepuration). Biomass separated by the culture medium is treated for the extraction of lipids containing different antioxidant carotenoids (such as astaxanthin and lutein) and starch granules as raw material for biopolymers

Microalgae cultivation for lipids and carbohydrates production

Microalgae are photoautotrophic microorganisms that can produce energy both by using sunlight, water and CO2 (phototrophic metabolism) and by using organic sources such as glucose (heterotrophic metabolism). Heterotrophic growth is a key factor in microalgae research, due to its increased productivity and the lower capital and operative costs compared to photoautotrophic growth in photobioreactors. Carbohydrate production from microalgae is usually investigated for the production of biofuels (e.g. bioethanol) by successive fermentation, but also other applications can be envisaged in biopolymers. In this work an increment in carbohydrate purity after lipid extraction was found. Protein hydrolysis for different microalgae strains (Scenedesmus sp. and Chlorella sp.) was investigated. Microalgae were cultivated under photoautotrophic or heterotrophic conditions, collecting biomass at the end of the growth. Biomass samples were dried or freeze dried and used for carbohydrate and lipid extraction tests. Lipid extraction was achieved using different organic solvents (methanol-chloroform and hexane-2propanol). Basic protein hydrolysis has been carried out testing different temperatures and NaOH concentrations values. Lipids were spectrophotometrically quantified, while residual biomass was saccharificated and the total amount of sugars was measured. Significant differences about the purity of extracted carbohydrates were found comparing dried with freeze dried biomass. However, not a very promising purification of carbohydrates was achieved after protein hydrolysis, asking for further analysis. © Copyright 2017, AIDIC Servizi S.r.l

Extraction of microalgal starch and pigments by using different cell disruption methods and aqueous two-phase system

AbstractBACKGROUNDMicroalgae can synthesize starch with productivity higher than conventional terrestrial crops, without the need for arable land. However, little is known about processes to extract starch from microalgae. Here, a biorefinery process is described including microalgal cell disruption followed by extraction of starch and pigments with aqueous two‐phase system (ATPS) using choline chloride and polypropylene glycol 400. Sonication and bead milling were compared for cell disruption rate and starch extraction efficiency.RESULTSA first order kinetic model described well the cell disruption for both the methods, with a rate 2.6 times higher for bead milling than sonication. By applying ATPS on samples with comparable cell disruption (>93%), starch was separated better after sonication (67% recovery in the pellet) than after bead milling, for which it remained equally distributed between pellet (40%) and choline chloride phase. Pigments were extracted with 42–66% yield irrespective of the cell disruption method. Microalgal starch granules had a normal and narrow distribution for size (0.93 ± 0.14 μm) and a gelatinization temperature between 45–55 °C.CONCLUSIONFor the same cell disruption yield, different starch separation efficiencies can be achieved, depending on the cell disruption method applied. Although bead milling was faster than sonication in disrupting cells, it gave worst starch separation efficiency. The properties of the extracted microalgal starch indicate potential technical advantages, with respect to conventional starch sources, for applications in the bioplastic and food sector. © 2021 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI)

Structured population balances to support microalgae-based processes: Review of the state-of-art and perspectives analysis

Design and optimization of microalgae processes have traditionally relied on the application of unsegregated mathematical models, thus neglecting the impact of cell-to-cell heterogeneity. However, there is experimental evidence that the latter one, including but not limited to variation in mass/size, internal composition and cell cycle phase, can play a crucial role in both cultivation and downstream processes. Population balance equations (PBEs) represent a powerful approach to develop mathematical models describing the effect of cell-to-cell heterogeneity. In this work, the potential of PBEs for the analysis and design of microalgae processes are discussed. A detailed review of PBE applications to microalgae cultivation, harvesting and disruption is reported. The review is largely focused on the application of the univariate size/mass structured PBE, where the size/mass is the only internal variable used to identify the cell state. Nonetheless, the need, addressed by few studies, for additional or alternative internal variables to identify the cell cycle phase and/or provide information about the internal composition is discussed. Through the review, the limitations of previous studies are described, and areas are identified where the development of more reliable PBE models, driven by the increasing availability of single-cell experimental data, could support the understanding and purposeful exploitation of the mechanisms determining cell-to-cell heterogeneity

Valorisation of Olive Pomace for the Production of Bio-Composite Adsorbents Applied in as Removal from Drinking Waters

Arsenic is a toxic metalloid representing a serious threat to human health, reaching a concentration in drinking water above the limit of 10 µg/L in many regions of the world. Although adsorption technologies are available today to remove arsenic from water, the employed adsorbents are expensive, which severely hinders the possibility of water treatment in marginal and rural areas. In this study, a two-stage process is investigated in which an adsorbent for the removal of arsenic from water is produced by hydrothermal carbonization (HTC) of olive pomace followed by iron precipitation. In the first part of the study, the kinetics of solid mass variation during the HTC process were analyzed to derive indications about the mechanisms driving the thermochemical conversion of olive pomace to hydrochar. It was thus verified that a satisfactory hydrochar yield could be attained after 30 min through the polymerization of hydrolysis products released during the early stages of HTC. Adsorption isotherms were determined for the Fe-hydrochar and the Fe-biochar produced by iron precipitation onto the hydrochar and the pyrolyzed olive pomace (biochar). Fe hydrochar showed higher adsorption capacity (qmax=8.7 mg/g) compared to the Fe-biochar (qmax= 5.3 mg/g). Fe-hydrochar was finally tested in a fixed-bed adsorption column for As removal, evidencing the ability to maintain the arsenic concentration below the 10 µg/L limit when employed in the configuration conventionally adopted for water treatment. However, in this configuration, the apparent adsorption capacity was reduced, indicating the need for an optimization of the fixed bed-column desig

Cultivation processes to select microorganisms with high accumulation ability

The 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

The 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