Table 3
Overview of different harvesting methods [6] and dry solids output concentration [20] and references
herein
Method
Process
Comments
Dry solids output
concentration (%)
Chemical
based
Precipitation/
flocculation
l
Addition of electrolytes or synthetic polymers
to neutralize negative surface charge
3–8
l
The use of metal salts for coagulation and
flocculation is cautioned due to potential
inhibition of the specific methanogenic activity
of methanogenic and acetogenic microbes
Mechanical
based
Centrifugation
l
Centrifugal forces are utilized to separate based
on density differences
10–22
l
Probably the most rapid and reliable method
of recovering suspended algae
l
Easy to operate
l
High investment and operating costs
Filtration
l
Often used for filamentous strains
2–27
l
For small, suspended algae tangential flow
filtration is considered to be more feasible
l
High costs and power requirements
Sedimentation
l
Low costs
0.5–3
l
Low reliability because of fluctuating density
of algal cells
l
Slow
Dissolved air
flotation
l
Air is released under high pressure and forms tiny
bubbles in the water column, which adhere to the
suspended matter causing the suspended matter
to float
n.a.
l
Has been proven in large scale
l
The additional use of flocculants might be
problematic for further processing of the algae
Electrical
based
Separation
based on
electrophoresis
l
No chemicals needed
n.a.
l
High power requirements and electrode costs
Biological
based
Autoflocculation l High pH and the consumption of dissolved CO 2
lead to co-precipitation of algal cells together
with calcium phosphate
n.a.
Bioflocculation
l
Flocculation caused by secretion of polymers
n.a.
Microbial
flocculation
l
Addition of flocculating microbes
n.a.
n.a. not available
Large Scale Cultivation of Microalgae
7
Overview of different harvesting methods [6] and dry solids output concentration [20] and references
herein
Method
Process
Comments
Dry solids output
concentration (%)
Chemical
based
Precipitation/
flocculation
l
Addition of electrolytes or synthetic polymers
to neutralize negative surface charge
3–8
l
The use of metal salts for coagulation and
flocculation is cautioned due to potential
inhibition of the specific methanogenic activity
of methanogenic and acetogenic microbes
Mechanical
based
Centrifugation
l
Centrifugal forces are utilized to separate based
on density differences
10–22
l
Probably the most rapid and reliable method
of recovering suspended algae
l
Easy to operate
l
High investment and operating costs
Filtration
l
Often used for filamentous strains
2–27
l
For small, suspended algae tangential flow
filtration is considered to be more feasible
l
High costs and power requirements
Sedimentation
l
Low costs
0.5–3
l
Low reliability because of fluctuating density
of algal cells
l
Slow
Dissolved air
flotation
l
Air is released under high pressure and forms tiny
bubbles in the water column, which adhere to the
suspended matter causing the suspended matter
to float
n.a.
l
Has been proven in large scale
l
The additional use of flocculants might be
problematic for further processing of the algae
Electrical
based
Separation
based on
electrophoresis
l
No chemicals needed
n.a.
l
High power requirements and electrode costs
Biological
based
Autoflocculation l High pH and the consumption of dissolved CO 2
lead to co-precipitation of algal cells together
with calcium phosphate
n.a.
Bioflocculation
l
Flocculation caused by secretion of polymers
n.a.
Microbial
flocculation
l
Addition of flocculating microbes
n.a.
n.a. not available
Large Scale Cultivation of Microalgae
7