also considered as an economically viable and environment-friendly treatment
option (Ungureanu et al. 2015). Phycoremediation involves the natural ability of
alga to uptake the nutrient, accumulate the heavy metals, and degrade the organic
contaminant via symbiotic interaction with aerobic bacteria. Algae resemble the
pigment of higher plants with higher photosynthetic efficiency; hence algae released
greater extent of oxygen in aquatic system and induce the aerobic degradation of
organic compounds (Majumder et al. 2015). Alga is found to have the ability to
utilize waste as nutritional source, and it reduces the pollutants through metabolic
and enzymatic processes. The xenobiotics and heavy metal pollution can be detoxified, transformed, and volatilized through the algal metabolic pathways (Gautam
et al. 2015). Therefore, biological method employing algae has various advantages
such as (i) minimum capital and operating cost compared to physicochemical/
oxidation process (Mane et al. 2011), (ii) true destruction of organic and inorganic
pollutants (Parameswari et al. 2010), (iii) oxidation of wide range of organic
compounds, (iv) removal of reduced inorganic compound, i.e., sulfides and ammonia (Praepilas and Pakawadee 2011), etc.
Biosorption is the dominant mechanism in uptake of heavy metals either by active
algal biomass (AAB) or passive algal biomass (PAB) and found as a cost-effective
solution to eliminate HMs from industrial effluent. In case of passive algal biomass,
biosorption doesn’t involve in metabolic pathway; however, it entirely depends on
interaction between the biomass and metal ion; hence it resembles with the binding
of metal ions through ion-exchange resins. Contrary to the ion-exchange resins,
biosorption involves various steps such as chelation, partial adsorption, complexation, micro-precipitation, etc. On the other hand, biosorption in active algal biomass
is carried out through energy-mediated transport of metal ions through the cell
membrane. The ability of metal sorption through various organisms has been widely
reviewed by researchers and concluded that PAB have massive potential to bind
metal ions from very low concentration in the external solution. It has also been
reported that biosorption is significant to remove toxic metal and at the same time,
recovery of valuable metals such as gold, silver, and radionuclides is also possible.
Regardless of various advantages with algal-based metal uptake, several drawbacks
(low biomass generation, cost-effective biomass production less effective to remediate various industrial wastewaters) are also associated with phycoremediation.
Therefore, phycoremediation coupled with effective cultivation system (solar-driven
open pond or close photobioreactor) requires extensive investigation (Kothari et al.
2017; Ahmad et al. 2017). The present review deals with the various aspects of HM
removal as well as factors affecting the metal removal efficiency.
2 Hazardous Effects of Heavy Metals
Heavy metals are considered to have hazardous effect on the flora and fauna. Key
source of heavy metals involving anthropogenic activities such as extraction, excavation, etc. is depicted in Fig. 3.1. Nonpoint source pollution such as haphazard
3 Phycoremediation: Algae as Eco-friendly Tools for the Removal of Heavy. . .
55
option (Ungureanu et al. 2015). Phycoremediation involves the natural ability of
alga to uptake the nutrient, accumulate the heavy metals, and degrade the organic
contaminant via symbiotic interaction with aerobic bacteria. Algae resemble the
pigment of higher plants with higher photosynthetic efficiency; hence algae released
greater extent of oxygen in aquatic system and induce the aerobic degradation of
organic compounds (Majumder et al. 2015). Alga is found to have the ability to
utilize waste as nutritional source, and it reduces the pollutants through metabolic
and enzymatic processes. The xenobiotics and heavy metal pollution can be detoxified, transformed, and volatilized through the algal metabolic pathways (Gautam
et al. 2015). Therefore, biological method employing algae has various advantages
such as (i) minimum capital and operating cost compared to physicochemical/
oxidation process (Mane et al. 2011), (ii) true destruction of organic and inorganic
pollutants (Parameswari et al. 2010), (iii) oxidation of wide range of organic
compounds, (iv) removal of reduced inorganic compound, i.e., sulfides and ammonia (Praepilas and Pakawadee 2011), etc.
Biosorption is the dominant mechanism in uptake of heavy metals either by active
algal biomass (AAB) or passive algal biomass (PAB) and found as a cost-effective
solution to eliminate HMs from industrial effluent. In case of passive algal biomass,
biosorption doesn’t involve in metabolic pathway; however, it entirely depends on
interaction between the biomass and metal ion; hence it resembles with the binding
of metal ions through ion-exchange resins. Contrary to the ion-exchange resins,
biosorption involves various steps such as chelation, partial adsorption, complexation, micro-precipitation, etc. On the other hand, biosorption in active algal biomass
is carried out through energy-mediated transport of metal ions through the cell
membrane. The ability of metal sorption through various organisms has been widely
reviewed by researchers and concluded that PAB have massive potential to bind
metal ions from very low concentration in the external solution. It has also been
reported that biosorption is significant to remove toxic metal and at the same time,
recovery of valuable metals such as gold, silver, and radionuclides is also possible.
Regardless of various advantages with algal-based metal uptake, several drawbacks
(low biomass generation, cost-effective biomass production less effective to remediate various industrial wastewaters) are also associated with phycoremediation.
Therefore, phycoremediation coupled with effective cultivation system (solar-driven
open pond or close photobioreactor) requires extensive investigation (Kothari et al.
2017; Ahmad et al. 2017). The present review deals with the various aspects of HM
removal as well as factors affecting the metal removal efficiency.
2 Hazardous Effects of Heavy Metals
Heavy metals are considered to have hazardous effect on the flora and fauna. Key
source of heavy metals involving anthropogenic activities such as extraction, excavation, etc. is depicted in Fig. 3.1. Nonpoint source pollution such as haphazard
3 Phycoremediation: Algae as Eco-friendly Tools for the Removal of Heavy. . .
55