Review Article
Microalgae as Sustainable Renewable Energy Feedstock for Biofuel Production
Table 3
Comparison between open ponds and photobioreactors [
51,
52,
58,
66ā
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 |
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