Advanced technique: Nano-bioremediation

Despite in-situ as well as ex-situ bioremediation techniques, some advanced technologies have come to the fore in recent years, but their- application is still limited (Haims et al. 2011, Amin et al. 2014). Nanotechnology is one of them and is characterized by microscopic manufactured particles (< 100 nm), called nanoparticles (NPS) or ultrafine particles (Zhang et al. 2003, Dong et al. 2013, Hong et al. 2017). NSP are atomic or molecular aggregates that can drastically modify then- physicochemical properties compared with the bulk material. The technique where nanoparticles/ nauomaterial are formed by plant, fungi, and bacteria with the help of nanotechnology, which are used to remove environmental contaminants (such as heavy metals, organic and inorganic pollutants) from contaminated sites, is called nano-bioremediation (Zhang et al. 2003, Singh and Walker 2006, Stafiej and Pyrzyuska 2007, Yadav et al. 2017). Table 5 below shows some plant nanoparticles used in the bioremediation of heavy metals of contaminated sites.

Nano-bioremediation is the emerging technique for the removal of pollutants for environmental clean-up. Prevailing technologies for contaminated-site remediation are chemical and physical remediation and incineration, including bioremediation (Varol et al. 2011). With recent advances, bioremediation offers an environmentally friendly and economically feasible option to remove contaminants from the environment (Mueller and Novvack 2010). Three main approaches are used in nano-bioremediation; it includes the use of microbes, plants, and enzymatic activities. Nanotechnology increases phytoremediation efficiency and can also be used for the eco-friendly restoration of soils, and water contaminated with heavy metals, organic and inorganic pollutants (Wang 2007, Rizwan et al. 2014, Yadav et al. 2017).

A new concept of single enzyme nanoparticles (SENs), related to nauoparticle, has been developed in which each enzyme molecule is contained by a hybrid organic/inorganic polymer network (Dong et al. 2013). Each enzyme molecule is modified with a porous organic/inorganic structure (or armor) of less than a few nanometers thick. This approach represents a new way to change and stabilize the enzymes, which form a new type of nanostructure as well (Chang et al. 2005, 2007, Hong et al. 2017). These nanoparticles have the potential to bind with the xenobiotic compounds and degrade them completely or transform in less harmful derivatives, which further help in cleaning the environment.

Recent studies have shown that organic contaminants such as atrazine, molinate. and chlorpyrifos can be degraded with nano-sized zero-valent ions (Zhang et al. 2003, Chang et al. 2005, 2007, Gliomiade et al. 2011). Nanoparticles in enzyme-based bioremediation can also be used in combination with phytoremediation (Novvack 2008, Singh et al. 2009, 2010, Shanna et al.

2018). For example, several complex organic compounds, such as long-chain hydrocarbons and

Table 5. Some plant nanoparticles used in bioremediation of heavy metals.

Plant species

Heavy metals

Noaea mucwnata

Pb (98%), Zn (79.03%), Cu (73.38%), Cd (72.04%) and N1 (33.61%)

Euphorbia macroclada

Pb (92%), Zn (76.05%), Cu (74.66), Cd (69.08%) and Ni (31.50%)

Source: Mohsenzadeh et aL (2012).

Table 6. Examples of the use of uanopaificles in remediation.

Process

exploited

Target compounds

Nanomaterials used

References

Adsorption

Heavy metals, organic compounds, arsenic, phosphate, Cr (IV), mercury, PAHs, DDT, Dioxin

Iron oxides, carbon-based nanomatenals such as dendruners and polymers, carbon nanotubes (CNTs)

(Bhaunnk et al. 2012, Pan et aL 2010, Mueller and Nowack 2009, 2010, Rickerby and Momson 2007, Stafiej and Pyrzynska 2007, Chang et al. 2005, 2007)

Photocatalysis

Organic pollutants, NOX, YOCs Azo dye, Congo red dye, 4-chlorophenol and Orange II, PAHs

Ti02, ZnO, species of non oxides (Fe III, Fe-,03, Fe04)

(Kliedr et al. 2009, Wang 2007, Baiidara et al. 2007, Banhnemann 2004, Kim et al. 2001, Feng et aL 2000)

Redox

reactions

Halogenated orgamc compounds, metals, nitrate, arsenate, oil, PAH, PCB

Nanoscale zero-valent non (nZYI), nanoscale calcium peroxide

  • (Zhang et al. 2003)
  • (Tratnyek and Johnson 2006) (Nowack 2008, Klunkova et al. 2008, Varansi et aL 2007)

Dismfection

Diamines, phenols formaldehyde, hydrogen peroxide, silver ions, halogens, glutaraldehyde, acridines

Nano silver/titanium dioxide (Ag/TiOs) and CNTs

(Amm et al. 2014, Mcdonnell et aL 1999)

Membranes

Chlomiated compounds, polyethylene,

1,2-dichlorobenzene, organic and inorganic solutes, halogenated organic solvents

Nano Ag'TiCb Zeolites/ Magnetite and CNTs

(Amm et al. 2014, Mcdonnell et aL 1999)

organochlorines, are particularly resistant to microbial and plant degradation. A combined approach involving nanotechnology and biotechnology could overcome this limitation: complex organic compounds would be degraded into simpler compounds by nano-encapsulated enzymes, which in turn would be rapidly degraded by the joint activities of microbes and plants. Table 6 below shows examples of the use of nanoparticles in the remediation of contaminated sites (Yadav et al. 2017).

 
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