14.6 Environmental Implications
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14.6.2 Chemical Consumption
Depending on the source of cellulose, the types and quantity of chemicals consumed could vary. From plants with lignified cell walls, mineral acids and alkali are
often required for delignification. The amount of chemical used also depends on the
grade of cellulose required. Cellulose with all lignin, lipids and extractives such as
proteins removed and cellulose with all the hemicellulose removed have different
requirements.
Sodium hydroxide is commonly used for removal of the non-cellulosic components, and toluene has also been used for removal of lipids while depigmentation
and further delignification are achieved using sodium hypochlorite. Sodium acetate
at high temperature can also be used for delignification. Sodium hydroxide and
sodium acetate can be neutralized during wastewater treatment, thereby limiting the
impact on environment pH. Toluene however is an organic solvent derived from fossil fuel during the production of gasoline and other products. Exposure to toluene
either through the respiratory tract, gastrointestinal tract through contamination of
soil, air or drinking water as a result of various forms of release into the environment. Toluene has been associated with neurological, reproductive and developmental adverse effects (Vulimiri et al. 2017). Being a volatile organic compound, use of
toluene in the production of cellulose from aquatic biomass will require additional
processes for treatment such as adsorption, condensation and catalytic oxidation
(Martinez de Yuso et al. 2013). Exposure limits and safety of the workers coming
in contact with the harmful chemical will also require additional precautions hence
additional cost.
Cellulose production in general requires use of a wide variety of chemicals in large
amounts for delignification. The process of extraction results in generation of solids
and some other chemicals as effluent, and some of these chemicals are unknown
due to the complex structure of lignocellulosic biomass. One advantage of cellulose
from algae and aquatic plant is the lower lignin content compared to, for example,
wood. For example, duckweed has a lignin content of 12.2% (Yadav et al. 2017).
This results in reduced requirements for the heavy chemicals and energy used in
delignification.
14.6.3 Methane Emission
While the process of cultivation of aquatic plants and algae can be considered as CO 2
emission negative, the process of decomposition of the biomass in nature leads to the
emission of methane, another greenhouse gas of concern (Heilig 1994). Controlled
degradation of isolated cellulose and utilization of the decomposition products as
fuel are the ways to minimize the release of methane to the environment from the
decomposition of aquatic plants and animals. Cellulose has been shown to have a
higher biomethane potential of the three lignocellulosic compounds (Li et al. 2018).
321
14.6.2 Chemical Consumption
Depending on the source of cellulose, the types and quantity of chemicals consumed could vary. From plants with lignified cell walls, mineral acids and alkali are
often required for delignification. The amount of chemical used also depends on the
grade of cellulose required. Cellulose with all lignin, lipids and extractives such as
proteins removed and cellulose with all the hemicellulose removed have different
requirements.
Sodium hydroxide is commonly used for removal of the non-cellulosic components, and toluene has also been used for removal of lipids while depigmentation
and further delignification are achieved using sodium hypochlorite. Sodium acetate
at high temperature can also be used for delignification. Sodium hydroxide and
sodium acetate can be neutralized during wastewater treatment, thereby limiting the
impact on environment pH. Toluene however is an organic solvent derived from fossil fuel during the production of gasoline and other products. Exposure to toluene
either through the respiratory tract, gastrointestinal tract through contamination of
soil, air or drinking water as a result of various forms of release into the environment. Toluene has been associated with neurological, reproductive and developmental adverse effects (Vulimiri et al. 2017). Being a volatile organic compound, use of
toluene in the production of cellulose from aquatic biomass will require additional
processes for treatment such as adsorption, condensation and catalytic oxidation
(Martinez de Yuso et al. 2013). Exposure limits and safety of the workers coming
in contact with the harmful chemical will also require additional precautions hence
additional cost.
Cellulose production in general requires use of a wide variety of chemicals in large
amounts for delignification. The process of extraction results in generation of solids
and some other chemicals as effluent, and some of these chemicals are unknown
due to the complex structure of lignocellulosic biomass. One advantage of cellulose
from algae and aquatic plant is the lower lignin content compared to, for example,
wood. For example, duckweed has a lignin content of 12.2% (Yadav et al. 2017).
This results in reduced requirements for the heavy chemicals and energy used in
delignification.
14.6.3 Methane Emission
While the process of cultivation of aquatic plants and algae can be considered as CO 2
emission negative, the process of decomposition of the biomass in nature leads to the
emission of methane, another greenhouse gas of concern (Heilig 1994). Controlled
degradation of isolated cellulose and utilization of the decomposition products as
fuel are the ways to minimize the release of methane to the environment from the
decomposition of aquatic plants and animals. Cellulose has been shown to have a
higher biomethane potential of the three lignocellulosic compounds (Li et al. 2018).