Environmental Engineering Reference
In-Depth Information
cattle feed. This prompted the farmers to start cultivating this crop in the western countries, and
now it occupies a sizable acreage. Today it meets almost half of the demand for sugar consumption
in the developed world.
29.2 suGarBeet as a suGar croP
Sugarbeet (
Beta vulgaris
L.) belongs to family Chenopodiaceae and is an important sugar crop of
the world second only next to sugarcane. This is a hardy crop. It is drought and heat tolerant and can
grow in saline conditions, although its cultivation is labor-intensive (Streibig et al. 2009). Sugarbeet
is a biennial plant predominately grown in temperate regions where beets are planted in spring and
harvested in autumn. When grown in warmer regions the beets are planted in autumn and harvested
in spring. The recent introduction of tropical sugarbeet has enabled its cultivation in tropical and
subtropical regions.
Sugarbeet has been grown for food and fodder (Clarke and Edye 1996) since ancient times, but
its value as a sugar crop was realized in the mid-18th century when a method for extracting sugar
from the beets was discovered. German chemist Andreas Marggraf discovered that beets contain
sucrose, which was similar to that produced from sugarcane. However, an efficient protocol was not
developed for another 50 years. In the late eighteenth century, one of Marggraf's students, Franz
Karl Achard, succeeded in developing efficient methodology for producing crystalline sugar from
sugarbeet on an industrial scale. It was the research effort of Karl Achard that established sugarbeet
as an economic source of sucrose in Europe. Karl Archard is now considered to be the father of the
sugarbeet industry (Ensminger and Konlande 1993).
29.3 extractIon oF suGar
Sugarbeet is harvested mechanically; a series of blades on harvesters cut off the top leaves and the
crown. The roots are then cleaned to remove attached soil before transportation. At the processing
plant, sugar content of the crop is determined, which in turn determines a grower's payment (Dodic
et al. 2009). After thorough cleaning, the beets are chopped into slices called “cossettes.” Sugar
from beets is removed through a diffusion process. The cossettes are mixed with hot water at
approximately 70°C for approximately 90 min. The sugar in the beets passes from the plant cells
into the surrounding water by diffusion. This sugar-containing water is referred to as “raw juice,”
and the left behind cossettes are called “pulp,” which is high in moisture but low in sugar content.
Remnant sugar from the pulp is squeezed out in a screw press to remove as much juice as possible.
This juice is used as part of the water in the diffuser, and the pulp is then sent to a drying plant
where it can be processed into other value-added products.
The raw juice needs to be cleaned before crystallization. This is done by a process called
“carbonation,” where the juice is mixed with milk of lime [calcium hydroxide, Ca(OH)
2
] and
bubbling carbon dioxide through the mixture. Small clumps of chalk start to form in the juice, and
as these clumps form, they collect much of the nonsugar from the mixture (Kenter and Hoffmann
2007). After removal of chalk particles, a clean sugar solution is left behind, which is called “thin
juice.” Thin juice is concentrated into “thick juice” by evaporation in a multistage evaporator. This
thick juice contains approximately 60% sucrose by weight. Thick juice is then fed into crystallizers
to form sugar crystals, and a centrifugation step separates the sugar crystals from the liquid molasses.
29.4 BIoethanol ProductIon From suGars
Biofuels produced from sugar and starch-rich crops (e.g., sugarcane, sugarbeet, and corn) are often
referred to as first-generation biofuels because these crops were the first candidates for bioethanol
production. The sugar extracted from these crops is fermented anaerobically to produce ethanol.
The trend of producing ethanol started from Brazil, where sugar production was much higher than
