Microalgae as Sustainable Renewable Energy Feedstock for Biofuel Production

Table 3

Comparison between open ponds and photobioreactors [51, 52, 58, 66–71].

Factor	Open ponds	Photobioreactors
Area-to-volume ratio	Large	Small
Algal species	Restricted	Flexible
Species selection	Growth competition	Shear resistance
Sterility	Low	High
Cultivation period	Limited	Extended
Water loss through evaporation	Possible	Prevented
Controlling of growth conditions	Very difficult	Easy
Light utilization efficiency	Poor/fair	Fair/excellent
Gas transfer	Poor	Low-high
Temperature	Highly variable	Required cooling
Temperature control	None	Excellent
Automatic cooling system	None	Built in
Automatic heating system	None	Built in
Cleaning	Not required	Required due to wall growth and dirt
Weather dependence	High	Medium
Process control and reproducibility	Limited	Possible within certain tolerance
Microbiology safety	None	UV
Harvesting efficiency	Low	High
Population density	Low	High
Biomass productivity	Low	High
Biomass quality	Variable	Reproducible
Air pump	Built in	Built-in
Hydrodynamic stress on algae	Difficult	Easy
Shear	Low	High
CO2 transfer rate	Poor	Excellent
Mixing efficiency	Poor	Excellent
Volumetric productivity	High	Low
Water loss	Very high	Low
O2 concentration	Low due to continuous spontaneous out gassing	Exchange device
CO2 loss	High	Low
Land required	High	Low
Capital investment	Small	High
Periodical maintenance	Less	More
Operating cost	Lower	Higher
Harvesting cost	High	Lower
Most costly parameters	Mixing	O2, temperature control
Scale-up technology for commercial level	Easy to scale up	Difficult in most PBR models