3 Physico-chemical Methods for Heavy Metal Removal
There are many physico-chemical methods such as chemical precipitation, flotation,
coagulation and flocculation, ion exchange, membrane filtration, ultra-filtration,
nano-filtration, reverse osmosis, electrolysis, electro-coagulation, and photocatalysis used to remove heavy metals from the contaminated medium (Saravanan
et al. 2017). However, every process has its pros and cons. All the above-mentioned
technologies are crucial for the removal of toxic heavy metals from contaminated
environments. Nevertheless, these above-mentioned technologies have some disadvantages such as incomplete removal, produce a large amount of toxic secondary
sludge, expensive, high-energy requirements, and eco-unfriendly. Besides, the
above techniques may be ineffective when the high concentration of metal in
wastewater (10–100 mg/L) (Mehta and Gaur 2005), therefore, the urgent need for
alternative methods.
4 Algae and Its Uses in Bioremediation
Phycology is the scientific study of algae (“phyco” Greek for “alga”) which are
photosynthetic organisms that vary from single cells to multi-cellular. Algae is a
primary producer, use Sunlight as an energy source and carbon dioxide as a carbon
source and make food and release oxygen into the atmosphere (Bansal et al. 2018).
Algae are defined as “thallophytes (plants lacking roots, stems, and leaves) that have
chlorophyll as their primary photosynthetic pigment and distributed in many regions
of the world, from being airborne or sub-aerial to being terrestrial or aquatic, either in
freshwater or marine habitats. Many are eukaryotic organism but the term used to
include cyanobacteria (blue-green algae), which are prokaryotic. Algae can be
divided into two categories depending on its size, macroalgae (can be seen without
the aid of a microscope) and microalgae (can be seen using only with the aid of a
microscope). Moreover, the number of algae estimated is to be one to ten million,
with a high percentage of the microalgae (Chu 2012). According to Packer (2009),
algae have very high carbon capturing, photosynthetic efficiencies, and metabolism
when compared to terrestrial plants (Suresh and Benor 2020). Using algae for the
elimination or biotransformation of contaminants from any environment called
phycoremediation and this technology is rising lately (Fig. 13.2).
5 Microalgae
Many algae are microscopic, unicellular, and exist single (Chlorella vulgaris), or in
chains (Anabaena), or groups (Volvox), and can be motile (Diatoms), or non-motile
(Coccoid). Depending on the species, their sizes can range from a few micrometers
272
A. Ayele et al.
There are many physico-chemical methods such as chemical precipitation, flotation,
coagulation and flocculation, ion exchange, membrane filtration, ultra-filtration,
nano-filtration, reverse osmosis, electrolysis, electro-coagulation, and photocatalysis used to remove heavy metals from the contaminated medium (Saravanan
et al. 2017). However, every process has its pros and cons. All the above-mentioned
technologies are crucial for the removal of toxic heavy metals from contaminated
environments. Nevertheless, these above-mentioned technologies have some disadvantages such as incomplete removal, produce a large amount of toxic secondary
sludge, expensive, high-energy requirements, and eco-unfriendly. Besides, the
above techniques may be ineffective when the high concentration of metal in
wastewater (10–100 mg/L) (Mehta and Gaur 2005), therefore, the urgent need for
alternative methods.
4 Algae and Its Uses in Bioremediation
Phycology is the scientific study of algae (“phyco” Greek for “alga”) which are
photosynthetic organisms that vary from single cells to multi-cellular. Algae is a
primary producer, use Sunlight as an energy source and carbon dioxide as a carbon
source and make food and release oxygen into the atmosphere (Bansal et al. 2018).
Algae are defined as “thallophytes (plants lacking roots, stems, and leaves) that have
chlorophyll as their primary photosynthetic pigment and distributed in many regions
of the world, from being airborne or sub-aerial to being terrestrial or aquatic, either in
freshwater or marine habitats. Many are eukaryotic organism but the term used to
include cyanobacteria (blue-green algae), which are prokaryotic. Algae can be
divided into two categories depending on its size, macroalgae (can be seen without
the aid of a microscope) and microalgae (can be seen using only with the aid of a
microscope). Moreover, the number of algae estimated is to be one to ten million,
with a high percentage of the microalgae (Chu 2012). According to Packer (2009),
algae have very high carbon capturing, photosynthetic efficiencies, and metabolism
when compared to terrestrial plants (Suresh and Benor 2020). Using algae for the
elimination or biotransformation of contaminants from any environment called
phycoremediation and this technology is rising lately (Fig. 13.2).
5 Microalgae
Many algae are microscopic, unicellular, and exist single (Chlorella vulgaris), or in
chains (Anabaena), or groups (Volvox), and can be motile (Diatoms), or non-motile
(Coccoid). Depending on the species, their sizes can range from a few micrometers
272
A. Ayele et al.