residual combustion and avoiding unscientific bottom fly ash dumping at the thermal
power plant sites could result in less water pollution with HMs. Furthermore, air
quality management could result in less particulate deposition on the soil and reduce
the contamination of the water systems. However, these are basically source reduction approaches, and several countries, especially the developing countries, are
facing challenges to adopt proper management practices of the wastes/emissions
caused by these sectors. Therefore, it is necessary to remove the HMs from water
using removal techniques. HMs in water can be mitigated from water through
several physical, chemical, biological, and ecological approaches. Among the HM
treatment methods such as chemical precipitation, physical separation, ion exchange,
membrane filtration, membrane distillation, and hybrid methods, adsorption-based
methods are economic and extensively used.
11.4.1 Membrane Processes
Membrane processes are dependent on hydrostatic pressure which is used to remove
suspended particles and high molecular weight solutes and allow water and low
molecular weight solutes to pass through. Retention of pollutants is determined by
membrane materials, membrane characteristics (such as pore size, surface charge,
and hydrophobicity), specific micropollutant characteristics, and membrane fouling.
Montmorillonite, kaolin, tobermorite, magnetite, silica gel, and alumina-based
nanofilter membrane can remove up to 97% of Cd(II); chitosan-coated magnetic
nanoparticles modified with α-ketoglutaric acid can remove 99.9% Cu(II); polymeric cation exchanger containing nano-Zr(HPO 3 -S) 2 can remove up to 84% of Pb
(II); acid-modified carbon can remove up to 93% of As(V); and polonite can remove
up to 98% of Mn(II) (Khulbe and Matsuura 2018). Forward osmosis (FO) uses a
semipermeable membrane and a highly concentrated draw solution (relative to that
of the feed solution) to filter dissolved contaminants from the water. Osmotic
pressure gradient is used as driving force for this separation. The draw solution
induces a net flow of water through the membrane into the draw solution, thus
effectively separating the water from its solutes. Reverse osmosis (RO) uses a high
hydraulic pressure which is applied on the treating water, and a high-pressureresistant membrane is used to filter the dissolved solutes. RO has a greater efficiency
as it can remove particles as small as 10 Å (angstroms) and colloidal particles.
Khulbe and Matsuura (2018) have proposed a FO process consisting of a thin-film
composite (TFC) FO membrane made from interfacial polymerization on a macro
void-free polyimide support and a novel bulky hydro-acid complex Na 4 [Co
(C 6 H 4 O 7 ) 2 ].2H 2 O (Na–Co–CA) which can remove Cr, As, Pb, Cd, Cu, and Hg
from water. Moradi et al. (2020) analyzed the HM removal using the PES/B-Cur
membranes prepared by integrating boehmite nanoparticles functionalized with
curcumin (B-Cur) into PES membrane and observed an increased removal capability. The membrane showed the maximum adsorption capacity of 35.01 mg/g for Pb,
32.20 mg/g for Ni, 31.12 mg/g for Cu, 29.08 mg/g for Fe, 27.08 mg/g for Zn, and
11 An Overview on Heavy Metal Contamination of Water System and Sustainable. . .
267
power plant sites could result in less water pollution with HMs. Furthermore, air
quality management could result in less particulate deposition on the soil and reduce
the contamination of the water systems. However, these are basically source reduction approaches, and several countries, especially the developing countries, are
facing challenges to adopt proper management practices of the wastes/emissions
caused by these sectors. Therefore, it is necessary to remove the HMs from water
using removal techniques. HMs in water can be mitigated from water through
several physical, chemical, biological, and ecological approaches. Among the HM
treatment methods such as chemical precipitation, physical separation, ion exchange,
membrane filtration, membrane distillation, and hybrid methods, adsorption-based
methods are economic and extensively used.
11.4.1 Membrane Processes
Membrane processes are dependent on hydrostatic pressure which is used to remove
suspended particles and high molecular weight solutes and allow water and low
molecular weight solutes to pass through. Retention of pollutants is determined by
membrane materials, membrane characteristics (such as pore size, surface charge,
and hydrophobicity), specific micropollutant characteristics, and membrane fouling.
Montmorillonite, kaolin, tobermorite, magnetite, silica gel, and alumina-based
nanofilter membrane can remove up to 97% of Cd(II); chitosan-coated magnetic
nanoparticles modified with α-ketoglutaric acid can remove 99.9% Cu(II); polymeric cation exchanger containing nano-Zr(HPO 3 -S) 2 can remove up to 84% of Pb
(II); acid-modified carbon can remove up to 93% of As(V); and polonite can remove
up to 98% of Mn(II) (Khulbe and Matsuura 2018). Forward osmosis (FO) uses a
semipermeable membrane and a highly concentrated draw solution (relative to that
of the feed solution) to filter dissolved contaminants from the water. Osmotic
pressure gradient is used as driving force for this separation. The draw solution
induces a net flow of water through the membrane into the draw solution, thus
effectively separating the water from its solutes. Reverse osmosis (RO) uses a high
hydraulic pressure which is applied on the treating water, and a high-pressureresistant membrane is used to filter the dissolved solutes. RO has a greater efficiency
as it can remove particles as small as 10 Å (angstroms) and colloidal particles.
Khulbe and Matsuura (2018) have proposed a FO process consisting of a thin-film
composite (TFC) FO membrane made from interfacial polymerization on a macro
void-free polyimide support and a novel bulky hydro-acid complex Na 4 [Co
(C 6 H 4 O 7 ) 2 ].2H 2 O (Na–Co–CA) which can remove Cr, As, Pb, Cd, Cu, and Hg
from water. Moradi et al. (2020) analyzed the HM removal using the PES/B-Cur
membranes prepared by integrating boehmite nanoparticles functionalized with
curcumin (B-Cur) into PES membrane and observed an increased removal capability. The membrane showed the maximum adsorption capacity of 35.01 mg/g for Pb,
32.20 mg/g for Ni, 31.12 mg/g for Cu, 29.08 mg/g for Fe, 27.08 mg/g for Zn, and
11 An Overview on Heavy Metal Contamination of Water System and Sustainable. . .
267