13.3 Availability of Raw Material
291
Aquatic plants which produce starch can accumulate biomass at a faster rate than
terrestrial plants. Duckweeds, for example, can double in biomass between 1 and
3 days (Li et al. 2016). The effect of factors such as light intensity and temperature
on the rate of accumulation from biomass has been studied by different researchers;
however, the effects of these factors depend on other complex factors such as origin
of the plant and adaptation to the previous environment, such that a particular trend
cannot be recommended. For example, that an increase in light intensity results in
higher starch accumulation for one species sourced from a particular region might
not mean the same species from a different origin will respond in the same manner.
Starch production by some aquatic plants can be further optimized by limiting the
growth of the plant biomass to only the starch yielding parts of the plant. This results
in the faster harvest and minimizes the growth of non-starch materials. For example, in an earlier study (Fujita et al. 1999), optimal turion growth is achieved at low
nutrient concentration and low spacing between plants that have been demonstrated
in another duckweed strain, W. arrhiza (rootless duckweed). The turion is a dormant
tissue and can remain dormant for long periods (up to a month) in the absence of
nutrients. The turion is rich in starch (65.65%) and relatively low in lignocellulosic
(12.82%), and this is desirable for isolation of the starch component and can be
grown with less nutrient compared to the whole plant. Duckweed turion can achieve
a starch productivity of up to 2.90 g/m
2 daily from a turion biomass accumulation
rate of 3.78 g/m
2 daily. The turion of S. polyrhiza, also commonly known as rootless duckweed or spotless watermeal, is another highly productive starch-producing
aquatic plant. 0.34 g of ethanol is obtainable per gram of its turion. The saccharified
starch achieved a sugar to ethanol conversion of 91.67% (Xu et al. 2018).
The water hyacinth is another aquatic plant with considerable starch content.
Starch is present within different parts of the plant with the highest starch content
present in the rhizomes while the roots have the least. There is also a moderate amount
of starch present in the stolons, leaves and peduncles (Penfound and Earle 1948).
Starch content in green macroalgae ranges between 1.59 and 21.44%. The starch
content is affected by growth conditions and varies from season to season. Up to
3.43 tonnes of starch can be obtained per hectare annually from offshore cultivation
of Ulva ohnoi green algae (Prabhu et al. 2019).
Several reports have shown that starch content in aquatic plants and algae can
be significantly increased through nutrient starvation (Prabhu et al. 2019; Rehman
and Anal 2018; Korzen et al. 2016; Andrade et al. 2004). Such potential for yield
improvement through biotechnology and agricultural technology makes aquaticsourced starch very promising for applications such as biofuel production, a process
which requires large quantities of starch. Starch content in algae can also be boosted
by controlling the wavelength of the light under which they grow. For example, Ulva
pertusa has been shown to have improved starch content in blue light (Muthuvelan
et al. 2002). Starch content in algae could be as much as 32% on a dry weight basis
as it is found in Ulva rigida (Korzen et al. 2016). Table 13.1 gives the starch content
from some aquatic sources, and Table 13.2 lists starch production rate in terrestrial
crops.
291
Aquatic plants which produce starch can accumulate biomass at a faster rate than
terrestrial plants. Duckweeds, for example, can double in biomass between 1 and
3 days (Li et al. 2016). The effect of factors such as light intensity and temperature
on the rate of accumulation from biomass has been studied by different researchers;
however, the effects of these factors depend on other complex factors such as origin
of the plant and adaptation to the previous environment, such that a particular trend
cannot be recommended. For example, that an increase in light intensity results in
higher starch accumulation for one species sourced from a particular region might
not mean the same species from a different origin will respond in the same manner.
Starch production by some aquatic plants can be further optimized by limiting the
growth of the plant biomass to only the starch yielding parts of the plant. This results
in the faster harvest and minimizes the growth of non-starch materials. For example, in an earlier study (Fujita et al. 1999), optimal turion growth is achieved at low
nutrient concentration and low spacing between plants that have been demonstrated
in another duckweed strain, W. arrhiza (rootless duckweed). The turion is a dormant
tissue and can remain dormant for long periods (up to a month) in the absence of
nutrients. The turion is rich in starch (65.65%) and relatively low in lignocellulosic
(12.82%), and this is desirable for isolation of the starch component and can be
grown with less nutrient compared to the whole plant. Duckweed turion can achieve
a starch productivity of up to 2.90 g/m
2 daily from a turion biomass accumulation
rate of 3.78 g/m
2 daily. The turion of S. polyrhiza, also commonly known as rootless duckweed or spotless watermeal, is another highly productive starch-producing
aquatic plant. 0.34 g of ethanol is obtainable per gram of its turion. The saccharified
starch achieved a sugar to ethanol conversion of 91.67% (Xu et al. 2018).
The water hyacinth is another aquatic plant with considerable starch content.
Starch is present within different parts of the plant with the highest starch content
present in the rhizomes while the roots have the least. There is also a moderate amount
of starch present in the stolons, leaves and peduncles (Penfound and Earle 1948).
Starch content in green macroalgae ranges between 1.59 and 21.44%. The starch
content is affected by growth conditions and varies from season to season. Up to
3.43 tonnes of starch can be obtained per hectare annually from offshore cultivation
of Ulva ohnoi green algae (Prabhu et al. 2019).
Several reports have shown that starch content in aquatic plants and algae can
be significantly increased through nutrient starvation (Prabhu et al. 2019; Rehman
and Anal 2018; Korzen et al. 2016; Andrade et al. 2004). Such potential for yield
improvement through biotechnology and agricultural technology makes aquaticsourced starch very promising for applications such as biofuel production, a process
which requires large quantities of starch. Starch content in algae can also be boosted
by controlling the wavelength of the light under which they grow. For example, Ulva
pertusa has been shown to have improved starch content in blue light (Muthuvelan
et al. 2002). Starch content in algae could be as much as 32% on a dry weight basis
as it is found in Ulva rigida (Korzen et al. 2016). Table 13.1 gives the starch content
from some aquatic sources, and Table 13.2 lists starch production rate in terrestrial
crops.