This article describes the ability of the Chlorella vulgaris BEIJ strain G-120 to produce hydrogen (H2) via both direct and indirect pathways without the use of nutrient starvation. Photobiological ...H2 production reached a maximum rate of 12 mL H2 L−1 h−1, corresponding to a light conversion efficiency (light to H2) of 7.7% (average 3.2%, over the 8-day period) of PAR, (photosynthetically active irradiance). Cells presented a maximum in vivo hydrogenase activity of 25.5 ± 0.2 nmoles H2 μgChl−1 h−1 and the calculated in vitro hydrogenase activity was 830 ± 61 nmoles H2 μgChl−1 h−1. The strain is able to grow either heterotrophically or photo autotrophically. The total output of 896 mL of H2 was attained for illuminated culture and 405 mL for dark cultures. The average H2 production rate was 4.98 mL L−1 h−1 for the illuminated culture and 2.08 mL L−1 h−1 for the one maintained in the dark.
•Chlorella produced H2 by direct photosynthesis without applying sulfur-starvation.•Chlorella G-120 strain can release H2 both in the light and in the dark.•Chlorella G-120 strain can be grown both autotrophically and heterotrophically.•Photobiological H2 production by strain G-120 reached 7.7% efficiency (H2 to light).•Photosynthetic rate of Chlorella G-120 surpassed that of C. reinhardtii CC-124.
Microalgae are excellent sources of biomass containing several important compounds for human and animal nutrition—proteins, lipids, polysaccharides, pigments and antioxidants as well as bioactive ...secondary metabolites. In addition, they have a great biotechnological potential for nutraceuticals, and pharmaceuticals as well as for CO
2
sequestration, wastewater treatment, and potentially also biofuel and biopolymer production. In this review, the industrial production of the most frequently used microalgae genera—
Arthrospira
,
Chlorella
,
Dunaliella
,
Haematococcus
,
Nannochloropsis
,
Phaeodactylum
,
Porphyridium
and several other species is discussed as concerns the applicability of the most widely used large-scale systems, solar bioreactors (SBRs)—open ponds, raceways, cascades, sleeves, columns, flat panels, tubular systems and others. Microalgae culturing is a complex process in which bioreactor operating parameters and physiological variables closely interact. The requirements of the biological system—microalgae culture are crucial to select the suitable type of SBR. When designing a cultivation process, the phototrophic production of microalgae biomass, it is necessary to employ SBRs that are adequately designed, built and operated to satisfy the physiological requirements of the selected microalgae species, considering also local climate. Moreover, scaling up microalgae cultures for commercial production requires qualified staff working out a suitable cultivation regime.
Key points
•
Large-scale solar bioreactors designed for microalgae culturing
.
•
Most frequently used microalgae genera for commercial production
.
•
Scale-up requires suitable cultivation conditions and well-elaborated protocols
.
Graphical Abstract
In this study we compared the biomass productivity and the chemical composition of the diatom Phaeodactylum tricornutum grown outdoors at different biomass concentrations, in open ponds and ...photobioreactors (PBRs). Optimal biomass concentration of 0.6 g L−1 and 1.0 g L−1 was found in open ponds and in PBRs, respectively. During summer the mean net areal biomass yield was 11.7 g m−2 day−1 and 13.1 g m−2 day−1 in open ponds and in PBRs, respectively. Night biomass loss was comparable (17.4% and 21.4% of the daylight productivity, in open ponds, and PBRs, respectively). Lipid content ranged between 25% and 27.5% of dry weight, and increased up to 34.7% of biomass grown in dense cultures (>0.6 g L−1 in ponds; >1.0 g L−1 in PBRs). In the evening they ranged between 21% and 31%, while a reduced amount was found in the morning – between 14.5% and 24%. An induction of the diadino–diatoxanthin cycle was observed in the cultures when they were grown at lower biomass concentrations, particularly in cultures grown in photobioreactors, indicating down-regulation of the photosynthetic apparatus due to high irradiance, which was confirmed by a sizeable reduction in the Fv/Fm ratio in the middle of day. It was found that the productivity of cultures was higher in photobioreactors compared to that in open ponds most likely as a result of a better light–dark regime experienced by the cells in short light-path tubular PBRs, which may have allowed a more efficient use of light.
•We compared productivities of Phaeodactlylum tricornutum cultures grown in closed and open systems outdoors.•We report the biochemical biomass composition of Phaeodactlylum grown at different biomass concentrations outdoors.•Diurnal cycle affected the lipid content, but not the fatty acid profile.
•Bioaccessibility of Se-AAs in Se-Chlorella was compared with other products.•Se-Chlorella is one of the food supplements with highest bioaccessibility (∼50%).•Disintegration increased ...bioaccessibility of Se-AAs, drying process had no effect.•In vitro bioaccessibility method in this study can be applied to other materials.
Selenium (Se) is an indispensable microelement in our diet and health issues resulting from deficiencies are well documented. Se-containing food supplements are available on the market including Se-enriched Chlorella vulgaris (Se-Chlorella) which accumulates Se in the form of Se-amino acids (Se-AAs). Despite its popular uses, data about the bioaccessibility of Se-AAs from Se-Chlorella are completely missing. In the present study, gastrointestinal digestion times were optimized and the in vitro bioaccessibility of Se-AAs in Se-Chlorella, Se-yeast, a commercially available Se-enriched food supplement (Se-supplement) and Se rich foods (Se-foods) were compared. Higher bioaccessibility was found in Se-Chlorella (∼49%) as compared to Se-yeast (∼21%), Se-supplement (∼32%) and Se-foods. The methods used in production of Se-Chlorella biomass were also investigated. We found that disintegration increased bioaccessibility whereas the drying process had no effect. Similarly, temperature treatment by microwave oven also increased bioaccessibility whereas boiling water did not.
The microalga
Chlamydopodium fusiforme
MACC-430 was cultured in two types of outdoor pilot cultivation units—a thin-layer cascade (TLC) and a raceway pond (RWP) placed in a greenhouse. This case ...study aimed to test their potential suitability for cultivation scale-up to produce biomass for agriculture purposes (e.g., as biofertilizer or biostimulant). The culture response to the alteration of environmental conditions was evaluated in “exemplary” situations of good and bad weather conditions using several photosynthesis measuring techniques, namely oxygen production, and chlorophyll (Chl) fluorescence. Validation of their suitability for online monitoring in large-scale plants has been one of the objectives of the trials. Both techniques were found fast and robust reliable to monitor microalgae activity in large-scale cultivation units. In both bioreactors,
Chlamydopodium
cultures grew well in the semi-continuous regime using daily dilution (0.20—0.25 day
−1
). The biomass productivity calculated per volume was significantly (about 5 times) higher in the RWPs compared to the TLCs. The measured photosynthesis variables showed that the build-up of dissolved oxygen concentration in the TLC was higher, up to 125–150% of saturation (%sat) as compared to the RWP (102–104%sat). As only ambient CO
2
was available, its shortage was indicated by a pH increase due to photosynthetic activity in the thin-layer bioreactor at higher irradiance intensities. In this setup, the RWP was considered more suitable for scale-up due to higher areal productivity, lower construction and maintenance costs, the smaller land area required to maintain large culture volumes, as well as lower carbon depletion and dissolved oxygen build-up.
Key points
•
Chlamydopodium was grown in both raceways and thin-layer cascades in pilot-scale.
•
Various photosynthesis techniques were validated for growth monitoring.
•
In general, raceway ponds were evaluated as more suitable for cultivation scale-up.
Graphical Abstract
Microscopic algae and cyanobacteria are excellent sources of numerous compounds, from raw biomass rich in proteins, oils, and antioxidants to valuable secondary metabolites with potential medical ...use. In the former Czechoslovakia, microalgal biotechnology developed rapidly in the 1960s with the main aim of providing industrial, high-yield sources of algal biomass. Unique cultivation techniques that are still in use were successfully developed and tested. Gradually, the focus changed from bulk production to more sophisticated use of microalgae, including production of bioactive compounds. Along the way, better understanding of the physiology and cell biology of productive microalgal strains was achieved. Currently, microalgae are in the focus again, mostly as possible sources of bioactive compounds and next-generation biofuels for the 21st century.
In this study, we aimed to set up and test two models of annular-column photobioreactors (AC-PBR 1 and AC-PBR 2) in order to produce microalgae for fish hatcheries. Both models with a different ...design were characterized by a short light-path and central LED light source providing homogenous illumination of thin culture layer, sufficient mixing, and continuous temperature control guaranteed a stable cultivation regime and high biomass productivity. The AC-PBR 1 is characterized by a culture thickness of 5.5 cm and the maximum irradiance of 1200 µmol photons m
−2
s
−1
while in AC-PBR 2, the culture layer was decreased to 4.6 cm and the maximum irradiance intensity could reach 1600 µmol photons m
−2
s
−1
. AC-PBR 1 and AC-PBR 2 were compared using the selected microalgae strain
Vischeria helvetica
(class Eustigmatophyceae) which is a suitable feed source for rotifers further used as a live food for fish larvae. The photosynthetic performance, biomass productivity, pigment content, and fatty acid profile were evaluated. The volumetric productivity under continuous illumination at optimal growth temperature reached 0.16 and 0.33 g DW L
−1
day
−1
, corresponding to an areal productivity of 12.4 and 18.9 g DW m
−2
day
−1
for AC-PBR 1 and AC-BR2, respectively.
The worldwide growing demand for energy permanently increases the pressure on industrial and scientific community to introduce new alternative biofuels on the global energy market. Besides the ...leading role of biodiesel and biogas, bioethanol receives more and more attention as first- and second-generation biofuel in the sustainable energy industry. Lately, microalgae (green algae and cyanobacteria) biomass has also remarkable potential as a feedstock for the third-generation biofuel production due to their high lipid and carbohydrate content. The third-generation bioethanol production technology can be divided into three major processing ways: (i) fermentation of pre-treated microalgae biomass, (ii) dark fermentation of reserved carbohydrates and (iii) direct “photo-fermentation” from carbon dioxide to bioethanol using light energy. All three technologies provide possible solutions, but from a practical point of view, traditional fermentation technology from microalgae biomass receives currently the most attention. This study mainly focusses on the latest advances in traditional fermentation processes including the steps of enhanced carbohydrate accumulation, biomass pre-treatment, starch and glycogen downstream processing and various fermentation approaches.
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•Chlorella is a robust strain often acting as an “invasive” species.•Eukaryotic microalgae inocula led to a more robust and stable community.•RWs favoured a higher community ...variability than TLCs.•Nostoc was maintained but the prokaryotic community was variable.•TLC design enhanced nitrification while RW denitrification.
Thin-layer (TL) photobioreactors (PBRs) are characterised by high productivity. However, their use is limited to lab/pilot-scale, and a deeper level of characterisation is needed to reach industrial scale and test the resistance of multiple microalgae. Here, the performance and composition of eight microalgal communities cultivated in the two main TLs design (thin-layer cascade (TLC) and thin-layer raceway pond (RW)) were investigated through Illumina sequencing. Chlorella vulgaris showed robustness in both designs and often acted as an “invasive” species. Inoculum and reactor type brought variability. Eukaryotic microalgae inocula led to a more robust and stable community (higher similarity), however, RWs were characterised by a higher variability and did not favour the eukaryotic microalgae. The only cyanobacterial inoculum, Nostoc piscinale, was maintained, however the community was variable between designs. The reactor design had an effect on the N cycle with the TLC and RW configurations, enhancing nitrification and denitrification respectively.
