Ecofriendly Application of Nanomaterials: Nanobioremediation -

Ecofriendly Application of Nanomaterials: Nanobioremediation

 Introduction:

Nanomaterials (NMs) find eco-friendly applications in environmental science, particularly in clean water provision and remediation of environmental contaminants. Bioremediation, a process utilizing biological agents like bacteria and fungi to degrade contaminants into less toxic forms, offers economic advantages, high efficiency, and selectivity to specific metals. Common bioremediation technologies include in situ and ex situ methods, such as bioventing, bioleaching, bioreactor, bioaugmentation, composting, biostimulation, land farming, phytoremediation, and rhizofiltration. In situ bioremediation treats contaminants at the site of occurrence, minimizing environmental releases and allowing treatment of larger volumes. Ex situ bioremediation involves excavating contaminated material before treatment, offering faster and more controllable processes for a broader range of contaminants and soil types. Both approaches contribute to addressing environmental pollution efficiently.

The Science of Bioremediation with Nanomaterial

Nanomaterials (NMs) offer several advantages in bioremediation due to their increased surface area, quantum effects, and surface plasmon resonance. Different metallic and non-metallic NMs, including single metal nanoparticles, bimetallic nanoparticles, and carbon-based nanomaterials, are utilized based on their reactivity and ability to penetrate contamination zones. Oxide-coated Fe0 nanoparticles enhance reactivity and break down contaminants like carbon tetrachloride into less toxic byproducts. TiO2 nanotubes and Pd(0) nanoparticles serve in photoelectrocatalytic reactions and reductive dechlorination, respectively. Magnetic nanoparticles functionalized with ammonium oleate immobilize microbial cells for efficient desulfurization. These applications span solid waste, groundwater, wastewater, hydrocarbons, soil, uranium, and heavy metal pollution remediation, showcasing the transformative potential of NMs in environmental cleanup.

Nanoiron and Its Derivatives in Bioremediation

Nanoscale zero-valent iron (NZVI) has shown effectiveness in the removal of toxic pollutants such as arsenic, chromium, lead, and chlorinated hydrocarbons from groundwater. Various formulations, including anionic hydrophilic carbon (Fe/C) and poly(acrylic acid)-supported (Fe/PAA) zero-valent iron nanoparticles (NPs), have been explored for dehalogenation of chlorinated hydrocarbons in both groundwater and soil. Reactive walls constructed with iron nanoparticles can intercept and degrade halogenated organic compounds in the path of a contaminated groundwater plume. Nickel-iron nanoparticles have been studied for the dehalogenation of trichloroethylene (TCE). The dechlorination capability of zero-valent iron extends to compounds like pentachlorophenol (PCP) and DDT, showcasing its potential for diverse pollutant remediation.

Dendrimers in Bioremediation

Dendrimers, derived from Greek words meaning “like a branch of a tree," are highly branched and monodisperse macromolecules. They were first reported in the 1980s and consist of a central core, interior branch cells, and terminal branch cells. Dendrimers have various proven and potential applications, including in water treatment and dye treatment industries. Researchers have proposed their use in composite materials, combining dendrimers with nanoparticles to enhance catalytic activity, reactivity, and surface area, making them suitable for applications in clean water recovery units. Specifically, poly(amidoamine) (PAMAM) dendrimers have been employed as efficient and non-toxic water treatment agents, demonstrating their potential in water purification processes. Additionally, dendrimers have been incorporated into porous ceramic filters for the removal of organic pollutants, resulting in hybrid organic/inorganic filter modules with high mechanical strength and surface area.

Nanocrystals, Carbon Nanotubes, and So Forth in Bioremediation

Carbon-based nanomaterials, such as nanocrystals and carbon nanotubes (CNTs), exhibit exceptional and tunable properties that make them valuable for various environmental applications. Single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), and hybrid carbon nanotubes (HCNTs) have been evaluated for the removal of ethylbenzene from aqueous solutions. SWCNTs demonstrated higher removal efficiency than MWCNTs and outperformed HCNTs, showcasing their potential as efficient adsorbents for ethylbenzene, contributing to environmental pollution prevention.

Additionally, cyclodextrins (CD) and carbon nanotubes have found applications in water treatment and pollutant monitoring. CD-co-hexamethylene-/toluene-diisocyanate polyurethanes and CNT-modified equivalents have been successfully employed to remove organic contaminants from water to low levels. Various materials, including calixarenes, thiacalixarenes, and CNT-based polymeric materials, have been synthesized and tested for their ability to remove both organic (e.g., p-nitrophenol) and inorganic pollutants (e.g., Cd2+, Pb2+) from water.

In the context of metal adsorption, CNTs immobilized by calcium alginate (CNTs/CA) demonstrated high copper removal efficiency, reaching 69.9% even at a lower pH of 2.1. The copper adsorption capacity of CNTs/CA was notable at 67.9 mg/g at a copper equilibrium concentration of 5 mg/L. Furthermore, carbon nanotubes have been utilized for the removal of nickel ions from water, and magnetic-MWCNT nanocomposites have been applied for the removal of cationic dye from aqueous solutions. These applications highlight the versatility and effectiveness of carbon-based nanomaterials in addressing various environmental challenges.

Single-Enzyme NPs in Bioremediation

Enzymes play a crucial role in bioremediation as biocatalysts, but their limited stability and short catalytic lifetimes pose challenges. To enhance enzyme performance, particularly in terms of stability and reusability, magnetic iron nanoparticles (MNPs) have been employed. In a study using trypsin and peroxides, these catabolic enzymes were attached to MNPs, forming uniform core-shell magnetic nanoparticles. The results demonstrated a significant increase in enzyme lifetime and activity, extending from a few hours to weeks. The MNP-enzyme conjugates exhibited enhanced stability, efficiency, and cost-effectiveness, as MNPs acted as a protective shield, preventing enzyme oxidation. Additionally, the high magnetization of MNPs allowed for efficient magnetic separation, contributing to increased enzyme productivity.

Engineered Polymeric NPs for Bioremediation of Hydrophobic Contaminants

Polymer nanonetwork particles, specifically poly(ethylene)glycol modified urethane acrylate (PMUA), have been engineered to address the sorption challenges of hydrophobic organic contaminants, including polycyclic aromatic hydrocarbons (PAHs) like phenanthrene (PHEN). These particles increase the effective solubility of PHEN and enhance its release from contaminated aquifer material. PMUA NPs, developed as a precursor chain, demonstrate the ability to improve the bioavailability of PHEN, leading to increased mineralization rates in water. The results indicate that PMUA particles not only enhance the release of sorbed and NAPL-sequestered PHEN but also accelerate its mineralization rate. The accessibility of contaminants within PMUA particles to bacteria suggests their potential for effectively enhancing in situ biodegradation rates in natural attenuation processes during remediation. Moreover, PMUA NPs exhibit stability in the presence of diverse bacterial populations, allowing for their reuse after binding and degradation of PHEN by bacteria. This technology holds promise for applications in pump-and-treat or soil washing remediation strategies, utilizing bioreactors for the recycling of extracted nanoparticles.

Engineered Polymeric NPs for Soil Remediation

Amphiphilic polyurethane nanoparticles (APU) have been engineered for the remediation of soil contaminated with hydrophobic organic groundwater contaminants like polynuclear aromatic hydrocarbons (PAHs). These particles are composed of polyurethane acrylate anionomer (UAA) or poly(ethylene glycol) modified urethane acrylate (PMUA) precursor chains, emulsified and cross-linked in water to form colloidal-sized particles (17−97 nm). APU particles exhibit the capability to enhance PAH desorption and transport, similar to surfactant micelles. However, unlike micelles, the individual cross-linked precursor chains in APU particles remain stable and are not free to sorb to the soil surface. The engineered APU particles can be designed with hydrophobic interior regions that show high affinity for contaminants such as phenanthrene (PHEN) and hydrophilic surfaces promoting particle mobility in soil. The affinity of APU particles for contaminants can be controlled by adjusting the size of the hydrophobic segment in the chain synthesis. Charge density or the size of pendent water-soluble chains on the particle surface regulates the mobility of colloidal APU suspensions in soil. This versatility in controlling particle properties offers the potential for producing different nanoparticles optimized for various contaminant types and soil conditions.

Biogenic Uraninite NPs and Their Importance for Uranium Remediation

Biogenic uraninite nanoparticles have attracted the interest of geoscientists due to their significance in bioremediation strategies, small particle size, and biological origin. Recent research has begun to unveil the chemical and structural complexities of these natural nanoparticles. Remarkably, despite their extremely small size, the molecular-scale structure, energetics, and surface-area-normalized dissolution rates of hydrated biogenic uraninite appear to be similar to those of larger-particle, abiotic, stoichiometric UO2. These findings hold important implications for understanding the role of size as a moderator of nanoparticle aqueous reactivity and its relevance to the bioremediation of subsurface uranium (VI) contamination.

Bioremediation (Phytoremediation) of Heavy Metal Pollution by NPs of Noaea Mucronata

In a field study conducted in a dried waste pool of a lead mine, native accumulator plants, including Noaea mucronata, were identified for their potential in heavy metal phytoremediation. Concentrations of toxic metals (Cu, Zn, Pb, Ni) in both soil and plants were determined using flame absorption atomic methods. The results indicated elevated metal concentrations in the soil compared to natural conditions. Noaea mucronata, belonging to Chenopodiaceae, was identified as the best accumulator of Pb and also demonstrated good accumulation of Zn, Cu, and Ni. Bioaccumulation experiments with nanoparticles derived from N. mucronata showed a significant decrease in heavy metal concentrations over three days, highlighting its bioremediation potential.

Conclusion

Salient features of NMs of different types such as metal NMs, oxide NMs, carbon NMs, polymer NMs, nanocomposite and biological NMs, their synthesis method, and examples are given. This paper mainly focuses on the importance of NMs in degradation of waste and toxic material, which will also decrease the cost of degradation of waste and toxic materials. NMs not only directly catalyze degradation of waste and toxic materials, which is toxic to microorganism, but also it also helps enhance the efficiency of microorganisms in degradation of waste and toxic materials. This also shows that phytoremediation can be applied in the removal of heavy toxic metal from contaminated soil. Therefore, based on the above discussion, it can be said that, like its applications in various other fields of sciences, it has immense applications in bioremediation too. Due to its powerful potential, it is expected that their application will increase at a great leap in the near future, and it will play a critical role in sustainable development.

Reference:

RIZWAN, M.D., SINGH, M., MITRA, C.K. AND MORVE, R.K., 2014. Ecofriendly application of nanomaterials: nanobioremediation. Journal of Nanoparticles, 2014, pp.1-7.