Augmentation of Atrazine biodegradation by two Bacilli immobilized on α-Fe2O3 magnetic nanoparticles

Abstract

In this study, a novel immobilizing carrier with α-Fe₂O₃ magnetic nanoparticles was developed and used for immobilization of atrazine-degrading bacterial isolates of Bacillus spp. Since the free cells of microorganisms generally not succeed to degrade pollutants; thus, extra treatments are alluring to make strides biodegradation. Scanning electron microscope (SEM) images appeared that after immobilization the bacterial cells were totally retained and entirely distributed on the surface of α-Fe₂O₃ magnetic nanoparticles_. The performance of α-Fe₂O₃ immobilized cells in atrazine (ATZ) degradation was compared with the free cells, which was about 90.56% in 20 days. Experimental results exhibited that ATZ could be degraded at a broad range of physicochemical parameters viz. pH (4.0 to 9.0), temperature (20 to 45 °C), ATZ concentration (50 to 300 mg L^-1) and agitation speed (50 to 300 rpm), which underlines that α-Fe₂O₃ immobilized cells could tolerate a higher range of ATZ concentration as compared to free cells. This research demonstrated that α-Fe₂O₃ could be applied as a potential carrier in cell immobilization and biodegradation of ATZ herbicide with greater efficiency.

Figure 1

Phylogenetic trees of B. badius ABP6 (a) and B. encimensis ABP8 (b) based on the 16S rRNA sequence alignments. Sequences were aligned using Clustal W, distances were calculated using the Kimura 2 parameter method. The trees were built using the neighbour joining method.

Figure 2

Flowchart for the synthesis of hematite (α-Fe₂O₃) nanoparticles by chemical precipitation method.

Figure 3

Characterization of chemically synthesized α-Fe₂O₃ nanoparticle: (a) XRD spectra (b) UV–Vis spectrum (c) FT-IR Spectrum of synthesized nanoparticle indicating the wave number of the main vibration modes.

Figure 4

SEM images shows (a) The α-Fe₂O₃ nanoparticles: before immobilization, (b) Free bacterial cells (c) α-Fe₂O₃ nanoparticle after immobilization with bacterial cells and the red arrows point the locations of α-Fe₂O₃ nanoparticles adhesion with bacterial cells.

Figure 5

Effects of (a) pH, (b) Temperature (°C), (c) Atrazine concentrations (mg L⁻¹) and (d) agitation speed (rpm) on biodegradation of atrazine by free and immobilized bacterial cells. (Treatment-1: α-Fe₂O₃ without bacterial cells, Treatment-2: free bacterial cells, Treatment-3: α-Fe₂O₃ immobilized bacterial cells). Error bars represent standard deviation of triplicate tests and Values are means of three replicates with standard deviation.

Figure 6

Percent degradation of atrazine by free and immobilized bacterial cells with different treatments. (Treatment 1: Control-MSM + Atrazine, Treatment 2: MSM + Atrazine + α-Fe₂O₃, Treatment 3: MSM + Atrazine + B. badius, Treatment 4: MSM + Atrazine + B. encimensis, Treatment 5: MSM + Atrazine + free bacterial consortium, Treatment 6: MSM + Atrazine + α-Fe₂O₃ immobilized bacterial consortium). Error bars represent standard deviation of triplicate tests and Values are means of three replicates with standard deviation.