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In the present study, magnesium peroxide (MgO2) nanoparticles were synthesized by electro-deposition process and characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The batch experiments were conducted to evaluate the MgO2 half-life (600 mg/L) in groundwater under various temperatures (4, 15, and 30 °C) and initial pH (3, 7, and 12). The effect of Fe2+ ions (enhanced oxidation) on the toluene remediation by MgO2 was also investigated. Nanoparticles were injected to sand-packed continuous-flow columns, and toluene removal (50 ppm) was studied within 50 days at 15 °C. The results indicated that the half-life of MgO2 at pH 3 and 12 were 5 and 15 days, respectively, in comparison to 10 days at the initial pH 7 and 15 °C. The nanoparticles showed 20 and 7.5 days half-life at 4 and 30 °C temperatures, respectively. Injection of Fe2+ ions indicated an impressive effect on toluene removal by MgO2, and the contaminant was completely removed after 5 and 10 days, in the batch and column experiments, respectively. Confocal laser scanning microscope (CLSM) analysis indicated that the attached biofilm had a significant role in the decontamination of groundwater. Comparison of bioremediation and enhanced oxidation resulted in a considerable insight into the application of magnesium peroxide in groundwater remediation.ᅟ [ABSTRACT FROM AUTHOR]

Horseradish peroxidase (HRP) with a variety of potential biotechnological applications is still isolated from the horseradish root as a mixture of different isoenzymes with different biochemical properties. There is an increasing demand for preparations of high amounts of pure enzyme but its recombinant production is limited because of the lack of glycosylation in Escherichia coli and different glycosylation patterns in yeasts which affects its stability parameters. The goal of this study was to increase the stability of non-glycosylated enzyme, which is produced in E. coli, toward hydrogen peroxide via mutagenesis. Asparagine 268, one of the N-glycosylation sites of the enzyme, has been mutated via saturation mutagenesis using the megaprimer method. Modification and miniaturization of previously described protocols enabled screening of a library propagated in E. coli XJb (DE3). The library of mutants was screened for stability toward hydrogen peroxide with azinobis (ethylbenzthiazoline sulfonate) as a reducing substrate. Asn268Gly mutant, the top variant from the screening, exhibited 18-fold increased stability toward hydrogen peroxide and twice improved thermal stability compared with the recombinant HRP. Moreover, the substitution led to 2.5-fold improvement in the catalytic efficiency with phenol/4-aminoantipyrine. Constructed mutant represents a stable biocatalyst, which may find use in medical diagnostics, biosensing, and bioprocesses. [ABSTRACT FROM AUTHOR]

Phenols are toxic products derived from a wide range of industrial activities and the entry of these contaminants into the environment is seriously hazardous for both human and aquatic ecosystems. This study presents the use of a phenol-degrading consortium surrounded in an innovative "Small Bioreactor Chambers" (SBCs) along with biostimulation for phenol bioremediation from contaminated groundwater. To investigate the effect of biostimulation, synthesized-calcium peroxide (Ca02) nanoparricies were applied. The phenol-degrading consortium, was successfully isolated froni a water well located in Iran. The highest growth rate and phenol degradation of the ph100-consortium were observed at 15 °C and pH 7.5 in the presence of 500 mg·L-1 of powdered CaO2 and 100 mg·L-1 of phenol as a sole source of carbon. Next-generation sequencing (NGS) analysis of the consortium revealed that Proteobacteria and Bacteroidetes with 75.3% and 16.2% relative abundance were the dominant phyla in the ph100-consortium, respectively. Experimental results indicated that 100% of the contaminant (100 mg·LF) was successfully removed from groundwater using encapsulated CaO2 within 60 days with the negligible negative impacts on the microbial population. Furthermore, the highest biodegradation percentage were achieved during incubation of SBCs a medium supplemented with 500 mg·L-1 CaO2 Powder in 25th days of experiment. These results provide certain evidence for a successful simultaneous application of biostimulation and bioaugmentation processes through SBCs for contaminated water treatinent. [ABSTRACT FROM AUTHOR]

Volatile Organic Compounds (VOCs) are within the main industrial air pollutants whose release into the atmosphere is harmful to the ecosystem and human health. Gas-phase photocatalytic degradation of ethylbenzene, an aromatic VOC emitted from various sources, has been investigated in this study using TiO2 nanoparticle-coated glass beads in an annular photoreactor. To use visible light irradiation, TiO2 nanoparticles were doped by nitrogen using urea. The results showed that nitrogen doping significantly increased the removal efficiency of ethylbenzene under visible light irradiation compared with the pure TiO2, so that the removal efficiencies between 75–100% could be yielded for the initial ethylbenzene concentrations up to 0.13 g/m3 under visible light which could be useful for improving indoor air quality. The UV irradiated reactor needed less residence time and much higher removal efficiencies could be yielded at high initial concentrations. When the residence time under UV irradiation was one third of the same under visible light, the removal efficiency was more than 80% for the inlet concentrations up to 0.6 g/m3, whereas the removal efficiency under visible light was about 25% at this inlet concentration. Langmuir-Hinshelwood kinetic model could be well fitted to the photocatalytic reaction in both irradiation systems. [ABSTRACT FROM AUTHOR]

One of the challenges in the petroleum hydrocarbon contaminated groundwater remediation by oxygen releasing compounds (ORCs) is to identify the remediation mechanism and determine the impact of ORCs on the environment and the intrinsic groundwater microorganisms. In this research, the application of encapsulated magnesium peroxide (MgO 2 ) nanoparticles in the permeable reactive barrier (PRB) for bioremediation of the groundwater contaminated by toluene and naphthalene was studied in the continuous flow sand-packed plexiglass columns within 50 d experiments. For the biodiversity studies, next generation sequencing (NGS) of the 16S rRNA gene was applied. The results showed that naphthalene was metabolized (within 20 days) faster than toluene (after 30 days) by microorganisms of the aqueous phase. By comparing the contaminant removal in the biotic (which resulted in the complete contaminant removal) and abiotic (around 32% removal for naphthalene and 36% for toluene after 50 d) conditions, the significant role of microorganisms on the decontamination process was proved. Furthermore, the attached microbial communities on the porous media were visualized by scanning electron microscopy (SEM). Microbial community structure analysis by NGS technique revealed that the microbial species which were able to degrade toluene and naphthalene such as P. putida and P. mendocina respectively were stimulated by addition of MgO 2 nanoparticles. The presented study resulted in a momentous insight into the application of MgO 2 nanoparticles in the hydrocarbon compounds removal from groundwater., (Copyright © 2018 Elsevier B.V. All rights reserved.)

This study investigated the applicability of synthesized calcium peroxide (CaO 2 ) nanoparticles for naphthalene bioremediation by permeable reactive barrier (PRB) from groundwater. According to the batch experiments the application of 400 mg/L of CaO 2 nanoparticles was the optimum concentration for naphthalene (20 mg/L) bioremediation. Furthermore, the effect of environmental conditions on the stability of nanoparticles showed the tremendous impacts of the initial pH and temperature on the stability and oxygen releasing potential of CaO 2 . Therefore, raising the initial pH from 3 to 12 elevated the dissolved oxygen from 4 to 13.6 mg/L and the stability of nanoparticles was significantly improved around 70 d. Moreover, by increasing the temperature from 4 to 30 °C, the stability of CaO 2 declined from 120 to 30 d. The continuous-flow experiments revealed that the naphthalene-contaminated groundwater was completely bio-remediated in the presence of CaO 2 nanoparticles and microorganisms from the effluent of the column within 50 d. While, the natural remediation of the contaminant resulted in 19.7% removal at the end of the experiments (350 d). Additionally, the attached biofilm on the surface of the PRB zone was studied by scanning electron microscopy (SEM) which showed the higher biofilm formation on the pumice surfaces in the bioremediation column in comparison to the natural remediation column. The physic-chemical characteristics of the effluents from each column was also analyzed and indicated no negative impact of the bioremediation process on the groundwater. Consequently, the present paper provides a comprehensive study on the application of the CaO 2 nanoparticles in PAH-contaminated groundwater treatment., (Copyright © 2018 Elsevier Ltd. All rights reserved.)