Chromium (VI) bioremoval from contaminated wastewater using Pseudomonas aeruginosa ATHA23 producing biofilm supported on clinoptilolite

More has yet to be investigated on the increased efficiency of microbes for the removal of heavy metals from industrial wastewaters. The objective was to determine the Cr (VI) bioabsorption and bioreduction ability of biofilm-producing bacteria supported on clinoptilolite from contaminated aqueous solutions. Chromium (VI)-tolerant bacteria, namely Pseudomonas aeruginosa ATHA23, were identified by biochemical methods and 16S rDNA sequencing and were deposited in NCBI (accession number: KF680991). Preparation of clinoptilolite, bacterial growth and isolation, biofilm production including extracellular polysaccharides (EPS) and Cr (VI) removal efficiency, affected by the experimental treatments, were investigated. The use of FTIR characterized clinoptilolite properties with and without biofilm in the presence and absence of Cr (IV). Higher Cr (VI) levels in the bacterial growth medium, increased EPS production with the highest value (0.171 mg L^-1), produced 18 h after treating the bacteria with Cr (VI) (100 mg L^-1). However, in the absence of Cr (VI), EPS significantly decreased to 0.117 mg L^-1. Plackett-Burman and Taguchi statistical analyses were used to optimize the experimental treatments affecting the removal efficiency of Cr (VI). Among the anions (nitrate, sulfate, and chloride), sulfate decreased Cr removal efficiency. The absorption data were best fitted to the pseudo-second order, and the data of Cr adsorption by clinoptilolite-biofilm were also better fitted to Freundlich isotherm model. The Cr (VI) bioremediation potential of P. aeruginosa ATHA23 by the production of biofilm supported on clinoptilolite has been shown for the first time, which is of significance for the environment and the industry.

Vermicomposting of sewage sludge with organic bulking materials to improve its properties

Adverse properties of sewage sludge such as high concentration of toxic metals and the presence of pathogens have limited its use in agriculture. In this study, the effect of vermicomposting on some important chemical properties of sewage sludge was investigated as a factorial arrangement based on a completely randomized design with three replications. The studied factors were bulking agents in three concentrations (0, 5, and 10% v/v), earthworm (Eisenia fetida) in 2 different concentrations (0 and 50 adult earthworms/6 kg sewage sludge), and retention times in three levels (30, 60, and 90 days). Sewage sludge was obtained from the lagoons of Ghahdarijan refinery in Isfahan province in Iran. The results showed that vermicomposting significantly (p < 1%) reduced the number of coliforms and concentrations of Ni, Cr, and Pb and increased the organic carbon percent and N of the sewage sludge. When comparing different treatments, vermicomposting of sewage sludge with rice husk 10% v/v during retention times of 60 and 90 days were superior treatments in reducing the concentrations of Ni, Cr, and Pb and reducing the number of coliforms. Furthermore, the highest %OC was measured in the rice husk 10% + earthworm in the retention time of 90 days which was about 41% more than the control treatment. In general, it is concluded that vermicomposting significantly reduced the adverse properties of sewage sludge for using in agriculture as an organic fertilizer.

The synergistic use of plant and isolated bacteria to clean up polycyclic aromatic hydrocarbons from contaminated soil

BACKGROUND

Biological methods of polycyclic aromatic hydrocarbons (PAH) contamination elimination typically involve the transformation of contaminants to non-toxic materials by microorganisms and plants and appear to be the most effective methods available.

METHODS

In this study, Bacillus licheniformis and Bacillus mojavensis isolated from oil-contaminated soils were inoculated onto Festuca arundinacea seeds before planting in the pot and 3 weeks after planting by syringe injection into the rhizospheric zone in order to study the elimination of PAHs from Festuca's rhizosphere in the greenhouse. Some physical and chemical properties of the soil, PAH concentrations, seeds germination percentage, root and shoot biomasses of the treated samples were examined.

RESULTS

The results showed that the treated samples inoculated with both bacteria had a significantly higher percentage of seed germination and root and shoot biomass compared to other treatments. The concentration of some PAHs reduced significantly (Pvalue < 0.05) in the rhizosphere of the treated samples inoculated with both bacteria compared to in contaminated soils. Concentrations of some PAHs (eg. Naphthalene, Phenanthrene, Benzo[a]anthracene and Dibenzo[a,h]anthracene) even reached below the detection limit of the method. The PAHs concentrations in the treated samples inoculated with bacteria was decreased significantly (Pvalue < 0.05). Therefore, the results showed the high efficiency of the Festuca and bacterial inoculation in eliminating PAHs from the soil.

CONCLUSION

According to the results, the partnership of Festuca with B. licheniformis and B. mojavensis isolates displayed positive effect on PAHs dissipation and can be effective cleanup technology with high performance.

Optimization of factors affecting hexavalent chromium removal from simulated electroplating wastewater by synthesized magnetite nanoparticles

Hexavalent chromium is a mutagen and carcinogen that is of significant concern in water and wastewater. In the present study, magnetite nanoparticles (n-Mag) were investigated as a potential remediation technology for the decontamination of Cr (VI)-contaminated wastewater. Synthesized n-Mag was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET-N2 technology. To screen and optimize the factors affecting Cr (VI) removal efficiency by synthesized nanoparticles, Plackett-Burman (PB) and Taguchi experimental designs were used respectively. The crystalline produced n-Mag was in the size range of 60-70 nm and had a specific surface area (SSA) of 31.55 m(2) g(-1). Results of PB design showed that the most significant factors affecting Cr (VI) removal efficiency were initial Cr (VI) concentration, pH, n-Mag dosage, and temperature. In a pH of 2, 20 mg L(-1) of Cr (VI) concentration, 4 g L(-1)of n-Mag, temperature of 40 °C, 220 rpm of shaking speed, and 60 min of contact time, the complete removal efficiency of Cr (VI) was achieved. Batch experiments revealed that the removal of Cr (VI) by n-Mag was consistent with pseudo-second order reaction kinetics. The competition from common coexisting ions such as NO₃(-), SO₄(2-), and Cl(-) were not considerable, unless in the higher concentration of SO₄(2-). These results indicated that the readily synthesized magnetite nanoparticles have promising applications for the removal of Cr (VI) from aqueous solution.