Advancement and Challenges in Harvesting Techniques for Recovery of Microalgae Biomass - Environmental Sustainability: Role of Green Technologies - page 158

Table 1 Comparison of different microalgae harvesting methods

Energy consumption
(kWh/m 3 ) Recovery Scale Benefi ts

Methods Limitations

Centrifugation 90 % Bench 8 Reliable, high solid

concentrate

Energy intensive, expensive

Flocculation 80-95 % Pilot 14.81-0.33 Good recovery Flocculants can be

expensive, may cause
contamination issues

Tangential fl ow
fi ltration

70-89 % Bench 0.38-2.06 Reliable, high solid

concentrate

Membrane fouling,
high cost

Dissolved air
fl otation

80-90 % Pilot 7.6 Proven in large scale Use of fl occulants may

create problems

Electrofl otation >95 % Bench - Effi cient recovery High cost, electrodes need

to be replaced periodically

Forward osmosis 80-92 % Pilot 0.3 Low energy input Slow and problems in

reverse solute fl ux

Magnetic
separation

90-98 % Bench - Rapid, less energy

intensive, and
environmental friendly

Complex fabrication and
expensive

Adapted from Christenson and Sims ( 2011 ), Xu et al. ( 2011 ), and Buckwalter et al. ( 2013 )

The recovery, energy consumption, and advantages
of different types of harvesting methods is shown
in Table 1 .

On the other hand, membrane fi ltration and
ultra- fi ltration are technically feasible for small-
sized algal cells (<30 mm) (Brennan and
Owende 2010 ).

3 Selection of Harvesting

Method 4 Harvesting Techniques

in Industry

Selection of able harvesting technology is a cru-
cial step for further downstream processing and
economic production of microalgal biomass
(Brennan and Owende 2010 ). The method must
be applicable to the harvesting of large volumes
of microalgae culture and must take into con-
sideration the acceptable amount of moisture
content in the product (Molina Grima et al. 2003 ).
The feasible product formation also intended to
choose a suitable technology for harvesting
microalgae biomass. The harvesting technology
is dependent on microalgae characteristics such
as size and density (Olaizola 2003 ). Selection of
strain must be taken into account for the pro-
cessing method, as the ease of harvesting varies
between species. For example, gravity settling
and conventional fi ltration processes are suit-
able for large-sized microalgal cells (>70 mm)
such as Coelastrum and Spirulina sp. (Brennan
and Owende 2010 ; Buckwalter et al. 2013 ).

The high commercial demand for microalgae for
wastewater treatment, production of biofuels,
and other value-added products have brought
forward the research and development of various
microalgae by private companies and industries
(Christenson and Sims 2011 ). Large-scale bio-
mass production under various cultivation systems
highlights the challenges of harvesting tech-
niques for further downstream processing. The
mass production of marine microalgae cyano-
bacteria Spirulina sp. has long been used for
various neutraceutical products. Companies
like Earthrise Nutritionals and Cyanotech are
involved in cultivating Spirulina sp. in open race-
way ponds in clean and non-wastewater systems
(Christenson and Sims 2011 ). Because of the
fi lamentous structure, simple fi ltrations methods
for harvesting Spirulina were very effective.
A patent application by Solix Biofuels and A2BE