algae production worldwide, owing to their flexibility, low cost, and easy of
scaling-up (Fernandez et al. 2013; Chang et al. 2017).
A raceway pond is a closed loop recirculation channel with a typical culture
depth of about 0.25–0.30 m. The circulation mixes the nutrients, and cells are
provided by the paddle wheels. The ponds are usually kept shallow because the
algae need to be exposed to sunlight, and sunlight can only penetrate the pond water
to a limited depth (Singh and Sharma 2012; Chang et al. 2017).
These ponds can be simply constructed in compacted soil with a 1- to
2-mm-thick plastic membrane. However, although it is cheaper, it is not commonly
used for biomass production due to the high risk of contamination (Singh and
Sharma 2012). To produce a biomass with high added value, the ponds are often
made of concrete block walls and dividers lined with a plastic membrane to prevent
seepage. Depending on the end use of the biomass, special care may be required to
use liners that do not leach contaminating and inhibitory chemicals into the algal
broth (Borowitzka 2005; Chisti 2016).
2.1.1 Major Factors Affecting the Raceway Pond Performance
Choice of Location
The choice of location of a raceway system has the greatest impact on biomass
productivity. The factors to consider in the geographic location are average annual
irradiance level, prevailing temperature, rainfall, land slope, potential nutrient
sources, cost of the water, and land.
In terms of illumination, a minimum solar irradiation of 4.65 kWh/m
2 /d is
required to sustain high growth rates (Benemann et al. 1982). According to Chisti
(2013), in an ideal condition, the temperature should be around 25 °C, with a
minimum of diurnal and seasonal variations. A geographic location with rainfall not
more than 1000 mm of rain per year facilitates the microalgae cultivation, since that
can minimize the dilution of algae stock in the ponds (Bennett et al. 2014). In an
ideal situation, the land slope should not be greater than 2% to avoid significant
earthmoving costs during pond construction, but the US Department of Energy
(DOE) cites a 5% maximum slope (DOE 2010; Bennett et al. 2014).
Other factor that depends on the local climate is the evaporation, which is
influenced by the level of irradiance, the wind velocity, the air temperature, and the
absolute humidity. An average freshwater evaporation rate of 10 L/m
2 /d has been
noted for some tropical regions. In this sense, freshwater needs to be added periodically to raceway to compensate the evaporation (Becker 1994; Chisti 2016).
Engineering Parameters
In raceways, the pond depth is one of the engineering parameters that has most
influence on cultivation performance, because it is closely related to temperature
2 Microalgal Production Systems with Highlights …
7
scaling-up (Fernandez et al. 2013; Chang et al. 2017).
A raceway pond is a closed loop recirculation channel with a typical culture
depth of about 0.25–0.30 m. The circulation mixes the nutrients, and cells are
provided by the paddle wheels. The ponds are usually kept shallow because the
algae need to be exposed to sunlight, and sunlight can only penetrate the pond water
to a limited depth (Singh and Sharma 2012; Chang et al. 2017).
These ponds can be simply constructed in compacted soil with a 1- to
2-mm-thick plastic membrane. However, although it is cheaper, it is not commonly
used for biomass production due to the high risk of contamination (Singh and
Sharma 2012). To produce a biomass with high added value, the ponds are often
made of concrete block walls and dividers lined with a plastic membrane to prevent
seepage. Depending on the end use of the biomass, special care may be required to
use liners that do not leach contaminating and inhibitory chemicals into the algal
broth (Borowitzka 2005; Chisti 2016).
2.1.1 Major Factors Affecting the Raceway Pond Performance
Choice of Location
The choice of location of a raceway system has the greatest impact on biomass
productivity. The factors to consider in the geographic location are average annual
irradiance level, prevailing temperature, rainfall, land slope, potential nutrient
sources, cost of the water, and land.
In terms of illumination, a minimum solar irradiation of 4.65 kWh/m
2 /d is
required to sustain high growth rates (Benemann et al. 1982). According to Chisti
(2013), in an ideal condition, the temperature should be around 25 °C, with a
minimum of diurnal and seasonal variations. A geographic location with rainfall not
more than 1000 mm of rain per year facilitates the microalgae cultivation, since that
can minimize the dilution of algae stock in the ponds (Bennett et al. 2014). In an
ideal situation, the land slope should not be greater than 2% to avoid significant
earthmoving costs during pond construction, but the US Department of Energy
(DOE) cites a 5% maximum slope (DOE 2010; Bennett et al. 2014).
Other factor that depends on the local climate is the evaporation, which is
influenced by the level of irradiance, the wind velocity, the air temperature, and the
absolute humidity. An average freshwater evaporation rate of 10 L/m
2 /d has been
noted for some tropical regions. In this sense, freshwater needs to be added periodically to raceway to compensate the evaporation (Becker 1994; Chisti 2016).
Engineering Parameters
In raceways, the pond depth is one of the engineering parameters that has most
influence on cultivation performance, because it is closely related to temperature
2 Microalgal Production Systems with Highlights …
7