of a biosorbent such as granular-activated carbon (GAC), natural clay materials such
as kaolinite and zeolite, biomass, and other natural and artificial materials (Borda and
Sparks 2008; Gadd 2009; Gaur et al. 2014).
6.4.1 Conventional Adsorbents
Recent adsorption technologies which act as possible alternatives and/or complementary to conventional technologies include granular-activated carbon (GAC),
nanotechnology, and biological adsorbent systems. GAC is the most commonly
used adsorbent due to its large surface area and high adsorption capacity attaining
high metal removal efficiency. However, the cost of production and regeneration of
spent carbon is still high and has limited its use in wastewater treatment (Babel and
Kurniawan 2004; Fu and Wang 2011). Nanotechnology offers great promise in
treatment of wastewater containing inorganic pollutants but faces some challenges
of cost-effectiveness and potential environmental and human risk (Qu et al. 2013).
The current cost of most nanomaterials is significantly high and owing to the small
size of these particles may facilitate transport of toxic materials in the environment
causing harm to cellular materials. Biological adsorbent systems use materials of
biological origin either dead or live for the treatment of wastewater containing heavy
metals. The technology can be categorized under biosorption and bioaccumulation.
6.4.2 Novel Biosorption of Metallic Species
The first major challenge in the biosorption field is to screen and select the most
promising biomass with high binding capacity for metals and possibility of reuse
(Kratochvil and Volesky 1998). A broad range of biomass types have been tested
including fungi, bacteria, yeast, and agricultural wastes such as cane molasses
(Abdel-Rahman et al. 2016), maize stalks (Haryanto et al. 2017), wood chips,
grass, and maize tassels (Guyo et al. 2015). The sorption of metals onto these
biomaterials is attributed to the constituents of the cell wall which are mainly
composed of carbohydrates, proteins, and phenolic compounds (Choi and Yun
2006).
The biosorption isotherms are used for basic evaluation of sorption systems under
optimal environmental conditions. Any comparison done at two different sorption
systems can only be done at the same initial concentration for screening of sorbents
with highest sorption capacity. These experiments are usually carried in batch
reactors as an initial step before application into the dynamic continuous systems
(Gadd 2009). Equilibrium isotherm models are classified into empirical and mechanistic equations. In the mechanistic models, mechanisms for biosorption are
explained and can predict the experimental behavior (Pagnanelli et al. 2001; Volesky
2007).
2 Advances in Bioremediation of Toxic Heavy Metals and Radionuclides in. . .
35
as kaolinite and zeolite, biomass, and other natural and artificial materials (Borda and
Sparks 2008; Gadd 2009; Gaur et al. 2014).
6.4.1 Conventional Adsorbents
Recent adsorption technologies which act as possible alternatives and/or complementary to conventional technologies include granular-activated carbon (GAC),
nanotechnology, and biological adsorbent systems. GAC is the most commonly
used adsorbent due to its large surface area and high adsorption capacity attaining
high metal removal efficiency. However, the cost of production and regeneration of
spent carbon is still high and has limited its use in wastewater treatment (Babel and
Kurniawan 2004; Fu and Wang 2011). Nanotechnology offers great promise in
treatment of wastewater containing inorganic pollutants but faces some challenges
of cost-effectiveness and potential environmental and human risk (Qu et al. 2013).
The current cost of most nanomaterials is significantly high and owing to the small
size of these particles may facilitate transport of toxic materials in the environment
causing harm to cellular materials. Biological adsorbent systems use materials of
biological origin either dead or live for the treatment of wastewater containing heavy
metals. The technology can be categorized under biosorption and bioaccumulation.
6.4.2 Novel Biosorption of Metallic Species
The first major challenge in the biosorption field is to screen and select the most
promising biomass with high binding capacity for metals and possibility of reuse
(Kratochvil and Volesky 1998). A broad range of biomass types have been tested
including fungi, bacteria, yeast, and agricultural wastes such as cane molasses
(Abdel-Rahman et al. 2016), maize stalks (Haryanto et al. 2017), wood chips,
grass, and maize tassels (Guyo et al. 2015). The sorption of metals onto these
biomaterials is attributed to the constituents of the cell wall which are mainly
composed of carbohydrates, proteins, and phenolic compounds (Choi and Yun
2006).
The biosorption isotherms are used for basic evaluation of sorption systems under
optimal environmental conditions. Any comparison done at two different sorption
systems can only be done at the same initial concentration for screening of sorbents
with highest sorption capacity. These experiments are usually carried in batch
reactors as an initial step before application into the dynamic continuous systems
(Gadd 2009). Equilibrium isotherm models are classified into empirical and mechanistic equations. In the mechanistic models, mechanisms for biosorption are
explained and can predict the experimental behavior (Pagnanelli et al. 2001; Volesky
2007).
2 Advances in Bioremediation of Toxic Heavy Metals and Radionuclides in. . .
35