6.3 Methylation
Partitioning of metallic species from the aquatic phase can be achieved through
biologically mediated methylation followed by volatilization. Detoxification by
methylation has been observed for mercury and selenium. For selenium, it is firstly
necessary to reduce all forms of selenium to elemental selenium (Se(0)) in order to
achieve methylation and volatilization. Methylation is identified as a critical step in
the transport of selenium out of terrestrial and aquatic environments contaminated
with selenium. Methylation occurs in water, sediment, and soil and is mostly a biotic
process. A wide range of organisms from bacterial, algal, and fungal groups are
capable of catalyzing the methylation process of selenium. Examples of the compounds that are formed from the methylation of selenium include dimethylselenide
(DMSe), dimethyldiselenide (DMDSe), dimethylselenone, trimethylselenonium,
selenous acid, selenium dioxide, and selenic acid, to name a few.
6.4 Biosorption
Traditional treatment technologies such as membrane filtration, GAC adsorption,
precipitation-sedimentation, flotation, ion-exchange, and electrochemical deposition
systems have been used for decades for the removal of toxic heavy metals from
water (Veglio et al. 2003; Wang et al. 2004; Aziz et al. 2008). Unfortunately, these
technologies are associated with high cost for processing of metal concentrations,
lack of specificity, production of large volumes of sludge, and low performance at
low metal concentrations (Kotrba 2011; Gaur et al. 2014). Adsorption processes are
proving to be the most efficient for advanced wastewater treatment (Anastopoulos
et al. 2015). Adsorption is a more advanced reaction-mediated process at the surface
Fig. 2.4 Conceptual representation of biologically catalyzed Cr(VI) reduction with A(III) as an
electron donor
34
E. M. Nkhalambayausi-Chirwa et al.
Partitioning of metallic species from the aquatic phase can be achieved through
biologically mediated methylation followed by volatilization. Detoxification by
methylation has been observed for mercury and selenium. For selenium, it is firstly
necessary to reduce all forms of selenium to elemental selenium (Se(0)) in order to
achieve methylation and volatilization. Methylation is identified as a critical step in
the transport of selenium out of terrestrial and aquatic environments contaminated
with selenium. Methylation occurs in water, sediment, and soil and is mostly a biotic
process. A wide range of organisms from bacterial, algal, and fungal groups are
capable of catalyzing the methylation process of selenium. Examples of the compounds that are formed from the methylation of selenium include dimethylselenide
(DMSe), dimethyldiselenide (DMDSe), dimethylselenone, trimethylselenonium,
selenous acid, selenium dioxide, and selenic acid, to name a few.
6.4 Biosorption
Traditional treatment technologies such as membrane filtration, GAC adsorption,
precipitation-sedimentation, flotation, ion-exchange, and electrochemical deposition
systems have been used for decades for the removal of toxic heavy metals from
water (Veglio et al. 2003; Wang et al. 2004; Aziz et al. 2008). Unfortunately, these
technologies are associated with high cost for processing of metal concentrations,
lack of specificity, production of large volumes of sludge, and low performance at
low metal concentrations (Kotrba 2011; Gaur et al. 2014). Adsorption processes are
proving to be the most efficient for advanced wastewater treatment (Anastopoulos
et al. 2015). Adsorption is a more advanced reaction-mediated process at the surface
Fig. 2.4 Conceptual representation of biologically catalyzed Cr(VI) reduction with A(III) as an
electron donor
34
E. M. Nkhalambayausi-Chirwa et al.