mitigating carbon dioxide through carbon dioxide fixation via photosynthesis (Pulz
and Gross 2004). Thus, the utilization of industrial emissions as carbon dioxide
source for microalgal growth proves to be a promising method for reduction of the
GHG emissions (Mata et al. 2010). Apart from carbon dioxide, sulfur oxides, and
nitrogen oxides, some heavy metals are also present in the flue gases that demand
further attention and proper removal. Microalgae play a crucial role for the removal
of these substances, thereby reducing the overall emission of GHG in the ecosystem
(Patel et al. 2017).
8.7.8 Nutrient Recycling from the Wastewater or Bioremediation
In the wastewater, nutrients are present which are used by the microalgae for their
growth (Mulbry et al. 2008; Roberts et al. 2013). Microalgae release the free oxygen
into wastewater during their growth, thereby enhancing the waste degradation by
other microorganisms. This results in improvement of the biochemical oxygen
demand (BOD) and chemical oxygen demand (COD) of the waste stream (Pittman
et al. 2011). These microalgae remove dissolved nitrogen, toxic metals, and phosphorous from the water and are thus used in the tertiary phase of wastewater
treatment (Munoz and Guieysse 2006; Rawat et al. 2011). Microalgae can also be
used for the degradation of persisting molecules such as antibiotics, heavy metals,
and hydrocarbons from the wastewater (Schwarzenbach 2006; Patel et al. 2017).
8.7.9 Effective Role of Microalgae in Improving Human Health
Microalgae synthesize various compounds which can be used as food colorants
(Becker 2013) and are a good source of food supplements as they are rich in
carbohydrates, lipid, and protein (e.g., Chlorella vulgaris composed of 51–58% of
carbohydrates, 14–22% of lipid, and 12–17% of protein (Spolaore et al. 2006;
Mathimani et al. 2018)). They are widely used as capsules or tablets and as
components of pastas, snacks, and beverages (Liang et al. 2004). Microalgae also
contain many types of sterols which are used to prevent the cardiovascular diseases,
for example, Spirulina sp. contain clionasterol which leads to enhanced synthesis of
plasminogen-activating factor in the endothelial cells of the vascular system (Barrow
and Shahidi 2008; Mata et al. 2010). Antioxidants, such as astaxanthin, carotenoids,
mycosporines, dimethylsulfoniopropionate, beta-carotene, etc., have also been
extracted from the microalgae. These antioxidants can prevent oxidative stress,
which is responsible for various diseases and contributes to the process of ageing.
Degenerative diseases can be further prevented and treated by carotenoids such as
lutein, which is commonly found in egg yolk, spinach, vegetables, kale, and other
yellow-colored foods. A high level of these carotenoids is present in Muriellopsis
sp. (Del et al. 2007; Mata et al. 2010). Owing to their high protein content,
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K. Agrawal et al.
and Gross 2004). Thus, the utilization of industrial emissions as carbon dioxide
source for microalgal growth proves to be a promising method for reduction of the
GHG emissions (Mata et al. 2010). Apart from carbon dioxide, sulfur oxides, and
nitrogen oxides, some heavy metals are also present in the flue gases that demand
further attention and proper removal. Microalgae play a crucial role for the removal
of these substances, thereby reducing the overall emission of GHG in the ecosystem
(Patel et al. 2017).
8.7.8 Nutrient Recycling from the Wastewater or Bioremediation
In the wastewater, nutrients are present which are used by the microalgae for their
growth (Mulbry et al. 2008; Roberts et al. 2013). Microalgae release the free oxygen
into wastewater during their growth, thereby enhancing the waste degradation by
other microorganisms. This results in improvement of the biochemical oxygen
demand (BOD) and chemical oxygen demand (COD) of the waste stream (Pittman
et al. 2011). These microalgae remove dissolved nitrogen, toxic metals, and phosphorous from the water and are thus used in the tertiary phase of wastewater
treatment (Munoz and Guieysse 2006; Rawat et al. 2011). Microalgae can also be
used for the degradation of persisting molecules such as antibiotics, heavy metals,
and hydrocarbons from the wastewater (Schwarzenbach 2006; Patel et al. 2017).
8.7.9 Effective Role of Microalgae in Improving Human Health
Microalgae synthesize various compounds which can be used as food colorants
(Becker 2013) and are a good source of food supplements as they are rich in
carbohydrates, lipid, and protein (e.g., Chlorella vulgaris composed of 51–58% of
carbohydrates, 14–22% of lipid, and 12–17% of protein (Spolaore et al. 2006;
Mathimani et al. 2018)). They are widely used as capsules or tablets and as
components of pastas, snacks, and beverages (Liang et al. 2004). Microalgae also
contain many types of sterols which are used to prevent the cardiovascular diseases,
for example, Spirulina sp. contain clionasterol which leads to enhanced synthesis of
plasminogen-activating factor in the endothelial cells of the vascular system (Barrow
and Shahidi 2008; Mata et al. 2010). Antioxidants, such as astaxanthin, carotenoids,
mycosporines, dimethylsulfoniopropionate, beta-carotene, etc., have also been
extracted from the microalgae. These antioxidants can prevent oxidative stress,
which is responsible for various diseases and contributes to the process of ageing.
Degenerative diseases can be further prevented and treated by carotenoids such as
lutein, which is commonly found in egg yolk, spinach, vegetables, kale, and other
yellow-colored foods. A high level of these carotenoids is present in Muriellopsis
sp. (Del et al. 2007; Mata et al. 2010). Owing to their high protein content,
226
K. Agrawal et al.