(equivalent to a laccase dose of 23 mg/L.d). Apart from enzyme reinjection, different
methods have been reported to minimize the loss of enzyme during operation of an
EMR. For example, ethylenediaminetetraacetic acid and polyethylene glycol, which
are believed to possess a protecting role for enzymes, especially under oxidative
stress, may be added to an EMR [40, 41]. While enzymes hold a great potential,
more research is needed to increase their stability before they can be implemented at
industrial scale.
2.1.3 Algae-Based Process
Microalgae have demonstrated potential for detoxifying a wide range of organic and
inorganic compounds at a range of scales, from laboratory through to full scale
[2]. Such detoxification typically occurs via three main pathways: bioadsorption,
where the compound is adsorbed to cell wall components or onto organic extracellular excretions; bio-uptake, where the compound is actively transported into the
cell; or biodegradation, where the compound is broken down into simpler molecules
through catalytic metabolic degradation [2]. While coupling NSAID bioremediation
with technologies such as microalgal wastewater treatment could potentially be
economically viable, there are several research challenges associated with
microalgal NSAID biodegradation that need to be overcome before this becomes a
viable option.
Detoxification via microalgal bioadsorption is dependent on the chemical structure of the compound, with hydrophobic, cationic compounds being attracted to the
microalgal cell surface through electrostatic interactions, whereas hydrophilic compounds are repelled [42]. Once at the cell surface, a number of chemical interactions
between the compound and the functional, charged groups on the cell surface may
occur, including adsorption reactions, ion exchange reactions with functional groups
on the microalgal surface, surface complexation reactions, chelation, and microprecipitation. However, NSAIDs are hydrophilic compounds, meaning that they are
anionic, or negatively charged, and have low bioadsorption affinity values with
microalgal cells due to the cells also being negatively charged [2]. This means that
the use of live microalgal cells for NSAID bioadsorption is not a viable option, but
the use of either physically or chemically modified nonliving cells may potentially
be a viable treatment option. Physical or chemical modifications can be made to the
microalgal cell surface that permits hydrophilic interactions between the hydroxyl
and carbonyl functional groups of the cell surface and the amino and carbonyl
groups in the molecules [2]. This can result in increased adsorption onto the cell
surface for hydrophilic compounds such as NSAIDs [2].
Adsorption of a non-NSAID hydrophilic drug (Tramadol) onto nonliving
microalgal cells was enhanced by 70% through simple chemical treatment (0.1 N
NaOH) of microalgal cell surfaces, compared to living microalgae [2]. Similarly,
Coimbra et al. [43] demonstrated that physically damaged (freeze-drying and grinding) nonliving microalgal cells were able to remove between 20 and 28 mg of
Contemporary Methods for Removal of Nonsteroidal Anti-inflammatory Drugs in. . .
223
methods have been reported to minimize the loss of enzyme during operation of an
EMR. For example, ethylenediaminetetraacetic acid and polyethylene glycol, which
are believed to possess a protecting role for enzymes, especially under oxidative
stress, may be added to an EMR [40, 41]. While enzymes hold a great potential,
more research is needed to increase their stability before they can be implemented at
industrial scale.
2.1.3 Algae-Based Process
Microalgae have demonstrated potential for detoxifying a wide range of organic and
inorganic compounds at a range of scales, from laboratory through to full scale
[2]. Such detoxification typically occurs via three main pathways: bioadsorption,
where the compound is adsorbed to cell wall components or onto organic extracellular excretions; bio-uptake, where the compound is actively transported into the
cell; or biodegradation, where the compound is broken down into simpler molecules
through catalytic metabolic degradation [2]. While coupling NSAID bioremediation
with technologies such as microalgal wastewater treatment could potentially be
economically viable, there are several research challenges associated with
microalgal NSAID biodegradation that need to be overcome before this becomes a
viable option.
Detoxification via microalgal bioadsorption is dependent on the chemical structure of the compound, with hydrophobic, cationic compounds being attracted to the
microalgal cell surface through electrostatic interactions, whereas hydrophilic compounds are repelled [42]. Once at the cell surface, a number of chemical interactions
between the compound and the functional, charged groups on the cell surface may
occur, including adsorption reactions, ion exchange reactions with functional groups
on the microalgal surface, surface complexation reactions, chelation, and microprecipitation. However, NSAIDs are hydrophilic compounds, meaning that they are
anionic, or negatively charged, and have low bioadsorption affinity values with
microalgal cells due to the cells also being negatively charged [2]. This means that
the use of live microalgal cells for NSAID bioadsorption is not a viable option, but
the use of either physically or chemically modified nonliving cells may potentially
be a viable treatment option. Physical or chemical modifications can be made to the
microalgal cell surface that permits hydrophilic interactions between the hydroxyl
and carbonyl functional groups of the cell surface and the amino and carbonyl
groups in the molecules [2]. This can result in increased adsorption onto the cell
surface for hydrophilic compounds such as NSAIDs [2].
Adsorption of a non-NSAID hydrophilic drug (Tramadol) onto nonliving
microalgal cells was enhanced by 70% through simple chemical treatment (0.1 N
NaOH) of microalgal cell surfaces, compared to living microalgae [2]. Similarly,
Coimbra et al. [43] demonstrated that physically damaged (freeze-drying and grinding) nonliving microalgal cells were able to remove between 20 and 28 mg of
Contemporary Methods for Removal of Nonsteroidal Anti-inflammatory Drugs in. . .
223