Microalgal Cultivation Reactor Systems - Biotechnological Applications of Microalgae - page 70

TABLE 5.5
Advantages and Disadvantages of Different Reactor Types

Reactor Type Advantages Disadvantages

Raceway Relatively economical

Low energy input
Easy to clean and maintain
No O 2 build-up
Large production capacity

Little control of culture conditions
Poor mixing
Light limitation
Readily contaminated
Limited growing period
Poor productivity
Large land area required
Limited CO 2 mass transfer with large
CO 2 losses to atmosphere if pond
sparged
Temperature determined by climate

Vertical column PBR Excellent mixing

High mass transfer rates
Low shear stress
Easy to clean and sterilize
Reduced photo-inhibition
Low cost
Low land area requirement

Low angle to incident sunlight
Size limited by area:volume ratio
Large mixing energy due to gas
compression

Tubular PBR Large illuminated surface area

Good biomass productivity
Relatively cheap construction
materials

Gradients of pH, O 2 , and CO 2
along tubes
Wall growth: fouling in tubes difficult to
clean
Large land area required
Significant water losses if evaporative
cooling is used
Possible hydrodynamic stress

Flat-plate PBR Large illuminated surface area

Short light path
Good biomass productivity
Easier to clean
Lower O 2 build-up

Scale-up requires many modules -
material intensive
Temperature control critical in thin
reactors

Source: From Borowitzka (1999); Pulz (2001); Chisti (2007); Ugwu et al. (2008); Brennan and
Owende (2010); Mata et al. (2010).

(Lee, 2001). To expand the product range, there is significant interest in the design
of closed reactors, particularly in the production of high-value, low-volume prod-
ucts requiring a high degree of sterility. The essence of the debate is presented in
Table 5.6 through a comparison of the key parameters of open and closed reactors.
Despite their higher cost and technical complexity, closed systems promise great
improvements in enhancing control over process parameters. The challenge appears to