reuse. Generally, if not biodegradable, they are discharged as part of wastewater to
the environment. In order to conserve energy resources and to reduce their environmental impact, surfactants should be recycled, particularly after industrial use.
Therefore, the development of surfactants with enhanced biodegradability and
recyclability using renewable resources under environmentally benign conditions
has been desired (Banno et al. 2013). With respect to green chemistry principles,
there is a tendency to substitute synthetic surfactants with naturally derived
alternatives. Microbial surfactants offer numerous benefits over synthetic ones.
Due to their versatility, biodegradability, low toxicity, high activity even under
extreme conditions (such as extreme pH and salinity), high effectivity in biodegradation and solubilization of low solubility compounds and mild production
conditions (Mulligan 2005; Morita et al. 2016; Costa et al. 2018; Inamuddin et al.
2021), they have been identified as promising agents in remediation technologies.
Unfortunately, a substantial portion of biodegradable materials are at a production
cost disadvantage against synthetic substances which limits their manufacture and
large-scale application.
Biosurfactants are surface-active compounds that are produced extracellularly or
as part of the cell membrane by bacteria, yeasts and fungi (Mulligan 2005) and due to
their remarkable properties they are considered multifunctional biomolecules of the
twenty-first century (Santos et al. 2016). All biosurfactants are amphiphilic
molecules with a polar (hydrophilic) moiety consisting of mono-, oligo- or
polysaccharides, peptides or proteins, and a non-polar (hydrophobic) group usually
containing saturated, unsaturated and hydroxylated fatty acids or fatty alcohols
(Lang 2002) that partition at liquid-liquid, liquid-gas or liquid-solid interfaces.
Such structure predestines them for the use in a range of industrial applications
where emulsification/de-emulsification, foaming, wetting, coating, detergency and
dispersion take place (Farn 2006; Santos et al. 2016). In recent years, emulsifying,
solubilizing and mobilizing (Usman et al. 2016) potential of biosurfactants has been
intensely explored for the remediation of different organic and inorganic environmental contaminants.
Biosurfactant ability of changing the surface and interfacial tensions and
stabilizing emulsions is a measure of its effectiveness, while critical micelle concentration (CMC) is commonly used to measure surfactant efficacy (Pacwa-Płociniczak
et al. 2011). CMC is a physical characteristic that indicates the concentration of
surfactant above which micelles start to form (IUPAC 1997). The lower the CMC,
the less surfactant is required to decrease the surface tension (Desai and Banat 1997),
i.e. to effectively emulsify, solubilize and disperse waste materials at the surface
(Abhijit 2017). The CMC of biosurfactants ranges from 1 to 2000 mg L
À1 (Santos
et al. 2016) and among surfactant types classified according to the composition of
their head (as non-ionic, anionic, cationic and amphoteric), the lowest CMCs are
generally found in the non-ionic category (Abhijit 2017). For instance, CMCs of
Triton X-100 and Triton X-114 – two high purity, inexpensive, commercially
available non-ionic detergents suitable for most biological applications used in our
experiment aimed at heavy metal removal from contaminated soils, are 0.24 and
0.2 mM, respectively.
5 The Recent Strategies Employed in Chemical Analysis of Contaminated Waters,. . .
149
the environment. In order to conserve energy resources and to reduce their environmental impact, surfactants should be recycled, particularly after industrial use.
Therefore, the development of surfactants with enhanced biodegradability and
recyclability using renewable resources under environmentally benign conditions
has been desired (Banno et al. 2013). With respect to green chemistry principles,
there is a tendency to substitute synthetic surfactants with naturally derived
alternatives. Microbial surfactants offer numerous benefits over synthetic ones.
Due to their versatility, biodegradability, low toxicity, high activity even under
extreme conditions (such as extreme pH and salinity), high effectivity in biodegradation and solubilization of low solubility compounds and mild production
conditions (Mulligan 2005; Morita et al. 2016; Costa et al. 2018; Inamuddin et al.
2021), they have been identified as promising agents in remediation technologies.
Unfortunately, a substantial portion of biodegradable materials are at a production
cost disadvantage against synthetic substances which limits their manufacture and
large-scale application.
Biosurfactants are surface-active compounds that are produced extracellularly or
as part of the cell membrane by bacteria, yeasts and fungi (Mulligan 2005) and due to
their remarkable properties they are considered multifunctional biomolecules of the
twenty-first century (Santos et al. 2016). All biosurfactants are amphiphilic
molecules with a polar (hydrophilic) moiety consisting of mono-, oligo- or
polysaccharides, peptides or proteins, and a non-polar (hydrophobic) group usually
containing saturated, unsaturated and hydroxylated fatty acids or fatty alcohols
(Lang 2002) that partition at liquid-liquid, liquid-gas or liquid-solid interfaces.
Such structure predestines them for the use in a range of industrial applications
where emulsification/de-emulsification, foaming, wetting, coating, detergency and
dispersion take place (Farn 2006; Santos et al. 2016). In recent years, emulsifying,
solubilizing and mobilizing (Usman et al. 2016) potential of biosurfactants has been
intensely explored for the remediation of different organic and inorganic environmental contaminants.
Biosurfactant ability of changing the surface and interfacial tensions and
stabilizing emulsions is a measure of its effectiveness, while critical micelle concentration (CMC) is commonly used to measure surfactant efficacy (Pacwa-Płociniczak
et al. 2011). CMC is a physical characteristic that indicates the concentration of
surfactant above which micelles start to form (IUPAC 1997). The lower the CMC,
the less surfactant is required to decrease the surface tension (Desai and Banat 1997),
i.e. to effectively emulsify, solubilize and disperse waste materials at the surface
(Abhijit 2017). The CMC of biosurfactants ranges from 1 to 2000 mg L
À1 (Santos
et al. 2016) and among surfactant types classified according to the composition of
their head (as non-ionic, anionic, cationic and amphoteric), the lowest CMCs are
generally found in the non-ionic category (Abhijit 2017). For instance, CMCs of
Triton X-100 and Triton X-114 – two high purity, inexpensive, commercially
available non-ionic detergents suitable for most biological applications used in our
experiment aimed at heavy metal removal from contaminated soils, are 0.24 and
0.2 mM, respectively.
5 The Recent Strategies Employed in Chemical Analysis of Contaminated Waters,. . .
149