290
13 Starch
13.3 Availability of Raw Material
Availability of starch is limited to some starch-producing aquatic plant and algae
biomass. Within this selection lies thousands of species and these include duckweeds, Azolla, water hyacinth macroalgae and microalgae. Duckweed, for example,
comprises of 37 species (Appenroth et al. 2013). Here we look at the availability of
starch from the aquatic environment based on the availability of these sources and
their starch component.
Duckweeds grow almost all year round with a growth season lasting between
9 and 12 months (Ziegler et al. 2015). Duckweed of up to 39.1–105.9 tonnes per
hectares annually is achievable with a starch content of up to 31.0–45.8%. 94.7% of
this starch can be converted into bioethanol, and duckweed is therefore a relatively
abundant source of starch. Methods such as selectively breeding high-performance
duckweed strains and improving starch enrichment in the plant are among the area
of research focus toward advancing duckweed for commercial production of starch
for biofuel application (Xu et al. 2014).
Duckweeds are exceptionally high in starch compared to other aquatic and nonedible plants in general. Duckweed species include Wolffia arrhiza (rootless duckweed), Spirodela polyrhiza (greater duckweed), Lemna gibba (fat duckweed), Lemna
minuta (least duckweed), Lemna minor (common duckweed), Lemna trisulca (ivyleaved duckweed). Duckweed annual accumulation estimated to 39.1–105.9 tonnes
of starch per hectare annually (Xu et al. 2012). They also have a relatively high
protein content. Their low lignin content is also a desirable feature as it makes the
extraction process less demanding. Accumulation of starch in duckweed is affected
by factors such as light intensity, temperature, nitrogen content and phosphorus content of the water within which they are growing. Adequate monitoring and control
of these parameters can improve the rate of starch accumulation.
Availability of biomass for starch production can be further improved by practicing a mixed culture system of aquatic farming. The productivity of biomass of
some aquatic plants can be improved by polyculture method. This involves growing
more than one strain of the plant within the same growth space. Duckweed polyculture comprising of Lemna aequinoctialis 5505, Landoltia punctata 5506 and S.
polyrhiza 5507 attained a starch composition of up to 28.78 g m
−2 . When compared
to monocultures of each species alone, the combination of all three gave a higher
starch biomass yield. However, the use of a polyculture does not always guarantee an
improvement in starch accumulation. This highly depends on the combination of the
species. While one combination of species in a polyculture could result in improved
starch content compared to monoculture, in a different combination of species the
starch accumulation could be less. For example, a monoculture of L. aequinoctialis
is grown at a temperature of 20 °C, light intensity of 105 µmol m
−2 s
−1 , nitrogen
concentration of 35 mg L
−1 and potassium concentration of 15 mg L
−1 which are
accumulated with 14.22 g of starch per m
2 of duckweed growth area. At the same
growth condition, the combination of all three species L. aequinoctialis, L. punctata
and S. polyrhiza attained a starch accumulation of 13.96 g m
−2 .
13 Starch
13.3 Availability of Raw Material
Availability of starch is limited to some starch-producing aquatic plant and algae
biomass. Within this selection lies thousands of species and these include duckweeds, Azolla, water hyacinth macroalgae and microalgae. Duckweed, for example,
comprises of 37 species (Appenroth et al. 2013). Here we look at the availability of
starch from the aquatic environment based on the availability of these sources and
their starch component.
Duckweeds grow almost all year round with a growth season lasting between
9 and 12 months (Ziegler et al. 2015). Duckweed of up to 39.1–105.9 tonnes per
hectares annually is achievable with a starch content of up to 31.0–45.8%. 94.7% of
this starch can be converted into bioethanol, and duckweed is therefore a relatively
abundant source of starch. Methods such as selectively breeding high-performance
duckweed strains and improving starch enrichment in the plant are among the area
of research focus toward advancing duckweed for commercial production of starch
for biofuel application (Xu et al. 2014).
Duckweeds are exceptionally high in starch compared to other aquatic and nonedible plants in general. Duckweed species include Wolffia arrhiza (rootless duckweed), Spirodela polyrhiza (greater duckweed), Lemna gibba (fat duckweed), Lemna
minuta (least duckweed), Lemna minor (common duckweed), Lemna trisulca (ivyleaved duckweed). Duckweed annual accumulation estimated to 39.1–105.9 tonnes
of starch per hectare annually (Xu et al. 2012). They also have a relatively high
protein content. Their low lignin content is also a desirable feature as it makes the
extraction process less demanding. Accumulation of starch in duckweed is affected
by factors such as light intensity, temperature, nitrogen content and phosphorus content of the water within which they are growing. Adequate monitoring and control
of these parameters can improve the rate of starch accumulation.
Availability of biomass for starch production can be further improved by practicing a mixed culture system of aquatic farming. The productivity of biomass of
some aquatic plants can be improved by polyculture method. This involves growing
more than one strain of the plant within the same growth space. Duckweed polyculture comprising of Lemna aequinoctialis 5505, Landoltia punctata 5506 and S.
polyrhiza 5507 attained a starch composition of up to 28.78 g m
−2 . When compared
to monocultures of each species alone, the combination of all three gave a higher
starch biomass yield. However, the use of a polyculture does not always guarantee an
improvement in starch accumulation. This highly depends on the combination of the
species. While one combination of species in a polyculture could result in improved
starch content compared to monoculture, in a different combination of species the
starch accumulation could be less. For example, a monoculture of L. aequinoctialis
is grown at a temperature of 20 °C, light intensity of 105 µmol m
−2 s
−1 , nitrogen
concentration of 35 mg L
−1 and potassium concentration of 15 mg L
−1 which are
accumulated with 14.22 g of starch per m
2 of duckweed growth area. At the same
growth condition, the combination of all three species L. aequinoctialis, L. punctata
and S. polyrhiza attained a starch accumulation of 13.96 g m
−2 .