indicates the propensity toward the formation of an oil-in-water emulsion, while low
HLB indicates the likely stabilization of a water-in-oil emulsion (Christofi and
Ivshina 2002; Van Hamme et al. 2006).
Synthetic surfactants are frequently used worldwide in bioremediation technologies as solvent washing enhancers and emulsifying agents for removal of organic
pollutants. Those technologies have been verified in both lab-scale and field-scale
studies; they have been applied in situ and ex situ (Sekhon et al. 2011). The
hydrophobic moiety of synthetic surfactants is represented by alkanes (paraffins),
alkenes (olefins), alkylphenols, alkylbenzenes, and alcohols. Poly(oxyethylenes),
sucrose, or polypeptides are common polar domains in nonionic surfactants, while
anionic surfactants contain sulfate, sulfonate, or carboxylate groups and cationic
surfactants contain a quaternary ammonium group (Sekhon et al. 2011). Sodium
dodecyl sulfate (SDS, anionic), Triton X-100, Tween 80, Brij 35, and Tergitol NP10
(neutral/non-ionic) are the most common synthetic surfactants successfully used in
remediation technologies (Bustamante et al. 2012).
Biosurfactants are natural agents produced predominantly by microorganisms,
but also by plants, e.g., fruit pericarp from Sapindus mukurossi (Roy et al. 1997),
soapberry-derived saponin (Maity et al. 2013), and soya lecithin (Fava et al. 2004).
They could also be in the form of specific natural molecules such as humic acids
(Conte et al. 2005) or waste materials such as humic substrates from compost
(Kulikowska et al. 2015a). As opposed to low molecular weight compounds commonly defined as biosurfactants, the amphiphilic molecules with high molecular
weight are called bioemulsifiers because of their specific behavior in oil/water
systems; owing to their high HLB values, biosurfactants usually make stable oilin-water emulsions (Calvo et al. 2009).
Similarly to synthetic surfactants, biosurfactants can be classified by their charge;
however, only few are cationic as anionic or neutral are the most common types. The
hydrophobic domains of biosurfactants are those of long-chain fatty acids or
hydroxylated fatty acids, while the hydrophilic moieties are represented by amino
acids, cyclic peptides, carboxylic acids, alcohols, phosphates, or carbohydrates
(Mulligan 2005). Bioemulsifiers, high-molecular-mass biosurfactants, consist of
amphipathic proteins, polysaccharides, lipoproteins, lipopolysaccharides, or complexes/combinations of those biopolymers (Calvo et al. 2009).
Microbial biosurfactants can be divided into several basic groups according to
their molecular structure including glycolipids (rhamnolipids, trehalolipids, and
sophorolipids); fatty acids, phospholipids; and neutral lipids (corynomycolic acid,
spiculisporic acid, and phosphatidylethanolamine); lipopeptides (surfactin and
lichenysin); and polymeric biosurfactants (emulsan, alasan, biodispersan, liposan,
and mannoprotein) (Pacwa-Płociniczak et al. 2011). Biosurfactants have a higher
level of specificity than chemical surfactants, which is caused by the wide diversity
of their basic chemical structures, e.g., lipids, glycolipids, phospholipids, fatty acids,
or peptide structures as well as by the broad variety of their functional groups and
detailed chemical structure, e.g., branching, number of functional groups or chains,
and carbon chain length.
24 Modern Bioremediation Approaches: Use of Biosurfactants, Emulsifiers. . .
497
HLB indicates the likely stabilization of a water-in-oil emulsion (Christofi and
Ivshina 2002; Van Hamme et al. 2006).
Synthetic surfactants are frequently used worldwide in bioremediation technologies as solvent washing enhancers and emulsifying agents for removal of organic
pollutants. Those technologies have been verified in both lab-scale and field-scale
studies; they have been applied in situ and ex situ (Sekhon et al. 2011). The
hydrophobic moiety of synthetic surfactants is represented by alkanes (paraffins),
alkenes (olefins), alkylphenols, alkylbenzenes, and alcohols. Poly(oxyethylenes),
sucrose, or polypeptides are common polar domains in nonionic surfactants, while
anionic surfactants contain sulfate, sulfonate, or carboxylate groups and cationic
surfactants contain a quaternary ammonium group (Sekhon et al. 2011). Sodium
dodecyl sulfate (SDS, anionic), Triton X-100, Tween 80, Brij 35, and Tergitol NP10
(neutral/non-ionic) are the most common synthetic surfactants successfully used in
remediation technologies (Bustamante et al. 2012).
Biosurfactants are natural agents produced predominantly by microorganisms,
but also by plants, e.g., fruit pericarp from Sapindus mukurossi (Roy et al. 1997),
soapberry-derived saponin (Maity et al. 2013), and soya lecithin (Fava et al. 2004).
They could also be in the form of specific natural molecules such as humic acids
(Conte et al. 2005) or waste materials such as humic substrates from compost
(Kulikowska et al. 2015a). As opposed to low molecular weight compounds commonly defined as biosurfactants, the amphiphilic molecules with high molecular
weight are called bioemulsifiers because of their specific behavior in oil/water
systems; owing to their high HLB values, biosurfactants usually make stable oilin-water emulsions (Calvo et al. 2009).
Similarly to synthetic surfactants, biosurfactants can be classified by their charge;
however, only few are cationic as anionic or neutral are the most common types. The
hydrophobic domains of biosurfactants are those of long-chain fatty acids or
hydroxylated fatty acids, while the hydrophilic moieties are represented by amino
acids, cyclic peptides, carboxylic acids, alcohols, phosphates, or carbohydrates
(Mulligan 2005). Bioemulsifiers, high-molecular-mass biosurfactants, consist of
amphipathic proteins, polysaccharides, lipoproteins, lipopolysaccharides, or complexes/combinations of those biopolymers (Calvo et al. 2009).
Microbial biosurfactants can be divided into several basic groups according to
their molecular structure including glycolipids (rhamnolipids, trehalolipids, and
sophorolipids); fatty acids, phospholipids; and neutral lipids (corynomycolic acid,
spiculisporic acid, and phosphatidylethanolamine); lipopeptides (surfactin and
lichenysin); and polymeric biosurfactants (emulsan, alasan, biodispersan, liposan,
and mannoprotein) (Pacwa-Płociniczak et al. 2011). Biosurfactants have a higher
level of specificity than chemical surfactants, which is caused by the wide diversity
of their basic chemical structures, e.g., lipids, glycolipids, phospholipids, fatty acids,
or peptide structures as well as by the broad variety of their functional groups and
detailed chemical structure, e.g., branching, number of functional groups or chains,
and carbon chain length.
24 Modern Bioremediation Approaches: Use of Biosurfactants, Emulsifiers. . .
497