1,720,970 research outputs found
From cells to flocs: a study of algal organic matter and bubble interactions in flotation-based harvesting of microalgal biomass
No full textHuman activities have irreversibly disrupted the ecological balance, primarily
by releasing vast amounts of CO2 into the atmosphere. This has
resulted in increases in global temperature and ocean acidification, and
therefore, thawing of the polar ice reserves, disturbance of the ocean’s
global conveyor belt, an increase in the frequency of extreme weather
events, and last but not least, loss of biodiversity. There is a pressing
need for eco-friendly methods of producing food and materials that do not
exacerbate climate change, considering the growth of the human population
and rising consumerism. Microalgae cultivation can play a crucial role
in these efforts.
Environmentally, with the rise of algal blooms, it is vital to efficiently
remove excess microalgae from water bodies before they decompose and
create an anoxic environment or release toxins. In this regard, coagulation
combined with flotation offers a promising solution to these challenges in
both freshwater and saline environments. Furthermore, microalgae cultivation
has the potential to replace many traditional biomass production
processes, using minimal land and water resources to address various
challenges faced by modern society. However, despite their ability to sequester
large amounts CO2, the valorization of microalgae biomass demands
high energy expenditures, which increases both the carbon footprint
and production costs. Hence, optimizing the harvesting process,
which accounts for a significant portion of the total costs, can result in
commercially competitive microalgae products and commodities.
A comprehensive investigation into the coagulation and flotation separation
of the model microalgal Chlorella species aims to improve the
efficiency of these processes. This study examines the biotechnological
aspects of microalgae, focusing on the interactions between cells, coagulants
and bubbles. Microalgae undergo changes in their intracellular and
cell wall composition as they absorb inorganic minerals and release organic
matter, known as AOM. These dynamic natural processes can affect the
coagulation and flotation efficiency of the algal biomass. Therefore, interdisciplinary
research integrating biology, chemistry, and material science is essential to uncover sustainable and efficient solutions for harvesting
microalgal biomass.
The methodology used in this study involves experimental testing of the
separation performance of the eco-friendly chitosan coagulant in combination
with flotation. Coagulation-flotation provides several advantages,
mainly that it is a process that is fast, highly concentrates the biomass, and
can be integrated in-line in scaled-up operations. The cells and the AOM
were analyzed to better understand their characteristics through chemical
and instrumental analyses relative to the separation response of the culture
and gain insight into the interplay between the biological and chemical
differences.
The findings highlight a strong influence of environmental conditions
and specific interactions between the chitosan, AOM, and the cell surface.
These interactions increase during the stationary growth phase, leading
to the formation of environments based on hydrogen bonding and electrostatic
interactions. The latter occurs when the chitosan’s amine groups are
protonated and interact with the acidic residues of polysaccharides present
in the AOM. Additionally, the impact of the growth phase (in terms of cells,
AOM, and medium) on floc formation and its characteristics was recorded.
This study revealed the advantages and disadvantages of different dosing
strategies of chitosan, depending on the growth phase. Findings also
endorse a strong influence of the environmental conditions in the experimental
set-up and the specific type of interaction of the functional groups
between chitosan, AOM, and the cell surface. It is inferred that the interaction
multiplies in the stationary phase of growth, creating environments
as described before.This work was supported by Research Foundation Flanders (FWO junior fundamental research project - G050220N, FWO scientific exchange program Tournesol - VS01322N)
Interference of AOM in coagulation of microalgae: influence of coagulant type and coagulation mechanism.
No full text
Interference of AOM in coagulation of microalgae: influence of coagulant type and coagulation mechanism.
No full textDissolved air flotation of a native Cuban Chlorella sp. using chitosan: influence of extracellular organic matter on coagulant dose and floc properties
No full text
Dissolved air flotation of a native Cuban Chlorella sp. using chitosan: influence of extracellular organic matter on coagulant dose and floc properties
No full textAlgae for Nanocellulose Production
No full textThe advantage of using algae biomass over traditional lignocellulosic biomass for nanocellulose production is based on its availability, its processing and its quality. However, it is currently only used in small quantities compared to traditional lignocellulosic-based nanocellulose. This chapter provides a detailed overview of the potential of algae as a resource for nanocellulose production. First, structural organization and biosynthesis pathways of cellulose are detailed for various groups of algae. The processing of microfibrillar cellulose, cellulose nanofibrils and cellulose nanocrystals from algae is discussed systematically. The exceptional properties of algae-based nanocellulose are mainly related to the high quality and purity. Nanocellulose crystallinity, thermal stability, degradation and rheological properties are highlighted and compared to wood-based counterparts. Finally, an overview of algal nanocellulose applications is given. Nanocellulose from algae can be of extremely high quality and reduce the complexity of processing associated with energy-savings when integrated in comprehensive biorefinery schemes for algae biomass. However, the selection of algae strains and the optimization of processing parameters remain critical in the control of the final nanocellulose properties
Chlorella sp. culture in coagulation and dissolved air flotation separation process using a poly-ε-Lysine coagulant
No full textHarnessing the cultivation and utilization of different microalgae is an ongoing global project since microalgae grow via photosynthesis. They can build organic molecules from inorganic compounds and solar energy, which, compared to plants, results in nutritious biomass rich in protein with a low water footprint. Microalgae harvesting technologies have seen significant technological advancement in the latest years. This progress has improved the feasibility of the microalgal biorefinery since they lead to a great reduction in harvesting costs. Coagulation-based harvesting research is directed to biobased coagulants that are sustainable, harmless, efficient, and inexpensive. Polysaccharide bio-polymers herd the greatest part of research publications, while limited literature is available for protein-based coagulants (1). It is hypothesized that protein and polypeptide coagulants could achieve high separation efficiencies due to their foaming properties.
A native Cuban Chlorella sp. strain (Universidad de Oriente, Cuba) was cultivated in BG-11 medium in 30L tubular photobioreactors. The growth was monitored on a dry weight basis, with an optical density of 750 nm (2). Coagulation and dissolved air flotation (C-DAF) jar tests were conducted on day 6 of growth in late-exponential phase biomass resuspended in fresh medium to 0.15 g/L dry weight at pH 8. The jar testing consisted of a homogenization (10 min, 200 rpm) with the addition of poly-ε-lysine (PL) (molecular weight: 3.5–4.5 kDa, Carbosynth, Ltd., Compton, UK) and floc growth phase (20 min, 20 rpm) followed by DAF (450 kPa, 31% recycle ratio) (Platypus DAF jar tester, Aquagenics Pty Ltd, Australia) in 1 L. The separation efficiency (η%) is the difference in absorbance of the subnatant at 750 nm. Zeta-potential and pH were measured in the Zetasizer Nano (Malvern Panalytical, UK) and the Knick PH-meter 764 Multi-Calimatic, respectively (3). Dissolved organic carbon (DOC) and total nitrogen (TN) were measured on the filtrate (0.45 μm PES membrane filter, VWR, Belgium) with the TOC-L analyser (Shimadzu, Germany). All solutions were freshly prepared for each experiment.
At 80 mg PL per g of algal biomass, there is a sudden increase in separation efficiency (89.5%), with the zeta potential increasing from -42.3 to -18.3 mV with weak foam formation. When increasing the dosage to 300 mg PL per g of algal biomass, the separation efficiency did not rise; the zeta potential increased slightly, reaching values closed to zero but did not become positive. The foam layer remained extremely thin. The pH dropped with an increasing dose of PL but did not go lower than 7. Similar observations were made by Noh et al. for a small-scale coagulation and sedimentation concept (4). The PL is positively charged at pH 8 and of low molecular weight; thus, it successfully produces flocs of small size, around 80 μm. The weak foam formation could be explained due to the 100% ratio of hydrophilic residues to the total number of residues which does not support the interaction with the bubble-air interface even though it is known to be slightly negative (5). Concluding, PL is prominent coagulant (electrostatic interactions with the cells) but not as efficient for flotation processes (weak hydrophobic interactions). Follow-up C-DAF tests with medium rich in organic matter could result in superior separation efficiencies since there might be a synergistic effect between the polypeptide and the extracellular organic matter.Acknowledgments to FWO, which financially supported this study with an FWO junior fundamental research project (2020-2021, G050220N, ) entitled “The presence of extracellular algal organic matter (AOM) in coagulation, flocculation and flotation processes for harvesting microalgae biomass: problem or opportunity?
Influence of extracellular algal organic matter on the flocculation sedimentation based recovery of microalgal biomass
No full text- …
