The document summarizes various techniques for harvesting microalgae biomass, including centrifugation, flocculation, auto-flocculation, chemical flocculation, electrical-based processes, gravity sedimentation, and flotation. Centrifugation uses centrifugal force to separate microalgal cells from suspension based on density. Flocculation involves aggregating dispersed microalgal cells into larger particles using chemicals or other means. Auto-flocculation is spontaneous aggregation without chemicals. Chemical flocculation uses salts like aluminum sulfate. Electrical-based processes use electrolysis. Gravity sedimentation relies on natural settling. Flotation takes advantage of microalgae's low density to float to the surface.

1. HARVESTING OF
MICROALGAE BIOMASS
Gomathi .M
First M.sc.Microbiology,
Department of Microbiology,
Vivekananda Arts and science College,
Sankagiri ..

2. SUB TOPICS:
• All harvesting techniques aim to remove as much culture media from
the microalgae biomass to facilitate next downstream processing such
as extraction of bioactive compounds.
• Microalgae are a group of microorganisms that have excellent
potential for a wide array of applications such as bioremediation
agents and feedstock for the production of fuel, bioactive
compounds.
• Cyanobacteria contain valuable compounds for health and cosmetic
applications.
• In another study, a harvesting efficiency of 89.9% was attained using
the buoy-bead flotation method.

3. CENTRIFICATION :
• In the case of microalgal harvesting, flocculation is considered as a
prerequisite step to achieve appropriate particle size for dewatering
using sedimentation or floatation or centrifugation.
• Microalgae centrifugation involves a phase separation of microalgal
cells from the suspension by the application of centrifugal force.
• The three main methods of separation are differential pelleting, rate-
zonal centrifugation and isopycnic centrifugation.
• A centrifuge operates by using the sedimentation principle- Here the
substances are separated based on their density under the influence
of gravitational force.

4. FLOCCULATION :
• During flocculation, the dispersed microalgal cells aggregate and form
larger particles with higher sedimentation rate.
• Flocculation can be induced in different ways. Induced chemical
flocculation using Zn2+, Al3+, Fe3+ or other chemical flocculants has
been studied extensively (McGarry 1970; Lee et al.
• Methods for causing the freely suspended algal cells to agglomerate,
or coagulate, into larger particles, or flocs, for rapid sedimentation by
gravity.
• The dispersed microalgal cells aggregate and form larger particles
with higher sedimentation rate.

6. AUTOFOCCULATUON :
• The microalgae suspension requires a concentration method, which is
most often done by centrifugation, filtration, and flocculation.
• Wherein microalgae can achieve up to 20%–30% moisture content
[67,68,94]; the choosing of the most adequate method will depend
not only on the economics.
• In auto-flocculation, suspended algal cells spontaneously aggregate,
forming large flocs, which induce their simple gravitational
sedimentation.
• A process by which a chemical coagulant added to the water acts to
facilitate bonding between particles, creating larger aggregates which
are easier to separate.

7. CHEMICAL FLOCCULATION :
• Induced chemical flocculation using Zn2+, Al3+, Fe3+ or other
chemical flocculants has been studied extensively (McGarry 1970; Lee
et al.
• Chemical flocculation of algae occurs due to charge neutralization and
electrostatic bridging between the suspended algal cells and the
applied flocculant(s).
• Aluminum sulfate or alum (Al2(SO4)3), ferric chloride (FeCl3) and
ferric sulfat.

9. ELECTICAL BASED PROCESS:
• One study reported that alkali-induced flocculation integrated with an
electrolysis (salt bridge electro-flocculation) approach was effectively
employed to harvest microalgae biomass.
• The production of single-cell algae and cyanobacteria, so called
‘microalgae’, has increased enormously over the last decades as the
utilization of microalgal biomass has expanded into various areas and
is slowly replacing conventionally produced biomass (crops, fish, etc.).
• Our target variables were: harvesting efficiency E (high), residual iron
in biomass cFe (low), energy costs Wm (low). The seven relevant
control parameters of the EC process were varied, to reach these
goals.

11. GRAVITY SEDIMENTATION :
• The freshwater microalgae Scenedesmus dimorphus was grown in a
modified BG11 medium (Zhang et al., 2012), and enlarging culture
was carried out in indoor 15 L photobioreactors at 25 ± 1 °C under
continuous fluorescent illumination with an intensity of
220 μmol·m−2·s−1.
• Microalgae is a promising feedstock of biofuel for alternating fossil
fuels. The major challenge of microalgal biofuels for commercial
applications is in designing an efficient harvesting method with high
economic feasibility.

13. FLOTATION :
• Flotation is known as a more effective and economic way to harvest
microalgae by taking advantage of their natural characteristics of relatively
low density and self-float
• Traditionally flotation is done either by air addition through adiffuser
(dispersed air flotation) or through pressurization (dis-solved air flotation)
[33,70]. A similar result can be achievedthrough the use of electrodes,
which is known as electrolytic flotation[64]. These methods are discussed
below.
• Most microalgae are negatively charged at nature pH values and show a
characteristic of low hydrophobicity, let alone with the hydrophilic DOM in
the medium. Thus, to increase the degree of hydrophobicity, the microalgal
cells.

15. THANK YOU 😊