A novel and economical approach for the synthesis of short rod-shaped mesoporous silica nanoparticles from coal fly ash waste by Bacillus circulans MTCC 6811.

Coal fly ash (CFA) is an industrial byproduct produced during the production of electricity in thermal power plants from the burning of pulverized coal. It is considered hazardous due to the presence of toxic heavy metals while it is also considered valuable due to the presence of value-added minerals like silicates, alumina, and iron oxides. Silica nanoparticles' demands and application have increased drastically in the last decade due to their mesoporous nature, high surface area to volume ratio, etc. Here in the present research work, short rod-shaped, mesoporous silica nanoparticles (MSN) have been synthesized from coal fly ash by using Bacillus circulans MTCC 6811 in two steps. Firstly, CFA was kept with the bacterial culture for bioleaching for 25 days in an incubator shaker at 120 rpm. Secondly, the dissolved silica in the medium was precipitated with the 4 M sodium hydroxide to obtain a short rod-shaped MSN. The purification of the synthesized silica particle was done by treating them with 1 M HCl at 120 °C, for 90 min. The synthesized short rod-shaped MSN were characterized by UV-vis spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Particle size analyzer (PSA), Field emission scanning electron microscopy (FESEM), and transmission electron microscope. The microscopic techniques revealed the short rod-shaped mesoporous silica nanoparticles (MSN) for the final nano-silica, whose size varies from 40 to 80 nm, with an average size of 36 ± 5 nm. The XRD shows the crystalline nature of the synthesized MSN having a crystallite size of 36 nm. The FTIR showed the three characteristic bands in the range of 400-1100 cm-1, indicating the purity of the sample. The energy dispersive X-ray (EDX) showed 53.04 wt% oxygen and 43.42% Si along with 3.54% carbon in the final MSN. The particle size analyzer revealed that the average particle size is 368.7 nm in radius and the polydispersity index (PDI) is 0.667. Such a novel and economical approach could be helpful in the synthesis of silica in high yield with high purity from coal fly ash and other similar waste.

Nanobioremediation: a bacterial consortium-zinc oxide nanoparticle-based approach for the removal of methylene blue dye from wastewater.

Industrial effluents carrying dyes are considered a major environmental threat in the present era. Methylene blue (MB) dye is one of the key dyes of the thiazine group of dyes. It is broadly used in medical, textile, and various fields and is well known for its carcinogenicity and methemoglobin nature. Bacterial and other microbes-mediated bioremediation is becoming an emerging and significant section for the treatment of wastewater. Isolated bacteria were used for the bioremediation and nanobioremediation of methylene blue dye under varying conditions and parameters. A comparative study was conducted for the remediation of methylene blue dye using bacterial consortium, potential bacteria (isolated by scale-up method), and potential bacteria within zinc oxide nanoparticles. The decolorizing ability of bacteria was analyzed by UV visible spectrophotometer after stirring and static incubation in different time intervals of the isolates. Growth parameters and environmental parameters which include pH, initial dye concentration, and dose of nanoparticles were optimized with the minimal salt medium. An enzyme assay study was also done to check the effect of dye and nanoparticles on bacterial growth and the mode of action of degradation. The authors found that potential bacteria within ZnO nanoparticles showed enhanced decolorization efficiency (95.46% at pH 8) due to the properties of nanoparticles. On the other hand, the decolorization of MB dye by potential bacteria and the bacterial consortium was about 89.08 and 76.3%, respectively, for a 10-ppm dye concentration. During the enzyme assays study, the highest activity was observed for phenol oxidase, nicotinamide adenine dinucleotide (NADH), 2,6-Dichloroindophenol(DCIP), and laccase for nutrient broth having MB dye, MB dye, and ZnO NPs, while no such change was observed for manganese peroxidase enzyme activity. Nanobioremediation is a promising approach to removing such pollutants from the environment.

Chlorpyrifos bioremediation in Pennisetum rhizosphere by a novel potential degrader Stenotrophomonas maltophilia MHF ENV20.

Rhizoremediation is a specific type of phytoremediation involving both plants and their rhizosphere associated microbes. In the present study Pennisetum pedicellatum and rhizosphere associated degrading strains were evaluated for chlorpyrifos remediation. Time-course pot experiments were conducted in greenhouse with P. pedicellatum grown in soil amended with chlorpyrifos at the concentrations of 10, 25, 50, 75 and 100 mg/kg for 60 days. The half life of chlorpyrifos varied from 19.25 to 13.02 days in planted treatments. Residual concentrations of chlorpyrifos were negatively correlated with abundance of degrading microorganisms in rhizosphere. The isolated species of Bacillus, Rhodococcus and Stenotrophomonas were evaluated for their degrading potential in mineral medium. A novel isolated strain of potential degrader Stenotrophomonas maltophilia named as MHF ENV20 showed better survival and degradation at high concentration of chlorpyrifos. Degradation of chlorpyrifos by strain MHF ENV20, 100, 50 and 33.3% degradation within the time period of 48 h (h), 72 and 120 h at 50,100 and 150 mg/kg concentrations, further the gene encoding the organophosphorous hydrolase (mpd) was amplified using PCR amplification strategy and predesigned primers. Our findings indicate that rhizosphere remediation is effective bioremediation technique to remove chlorpyrifos residues from soil. P. pedicellatum itself, in addition to the rhizosphere bacterial consortium, seemed to play an important role in reducing chlorpyrifos level in soil. High chlorpyrifos tolerance and rhizospheric degradation capability of P. pedicellatum, makes this plant suitable for decontamination and remediation of contaminated sites. The ability to survive at higher concentration of chlorpyrifos and enhanced degrading potential due to presence of mpd gene make S. maltophilia MHF ENV20 an ideal candidate for its application in chlorpyrifos remediation.

Benzene bioremediation using cow dung microflora in two phase partitioning bioreactor.

Bioremediation of benzene has been carried out using cow dung microflora in a bioreactor. The bioremediation of benzene under the influence of cow dung microflora was found to be 100% and 67.5%, at initial concentrations of 100mg/l and 250 mg/l within 72 h and 168 h respectively; where as at higher concentration (500 mg/l), benzene was found to be inhibitory. Hence the two phase partitioning bioreactor (TPPB) has been designed and developed to carry-out biodegradation at higher concentration. In TPPB 5000 mg/l benzene was biodegraded up to 50.17% over a period of 168 h. Further the Pseudomonas putida MHF 7109 was isolated from cow dung microflora as potential benzene degrader and its ability to degrade benzene at various concentrations was evaluated. The data indicates 100%, 81% and 65% degradation at the concentrations of 50mg/l, 100mg/l, 250 mg/l within the time period of 24h, 96 h and 168 h respectively. The GC-MS data also shows the presence of catechol and 2-hydroxymuconic semialdehyde, which confirms the established pathway of benzene biodegradation. The present research proves the potential of cow dung microflora as a source of biomass for benzene biodegradation in TPPB.

Occupational exposure to dust in quartz manufacturing industry.

Owing to the abundance of a sedimentary rock, 65 small-scale quartz manufacturing enterprises, employing 650 workers, have been established in the region studied. Quartz powder manufacturing involves various processes and operations, such as manual handling of quartz stones, crushing, grinding, sieving, screening, mixing, storing and bagging. Results demonstrate that each of these operations generates high concentrations of airborne 'total' dust and respirable dust, which contain a very high percentage (> 75%) free silica. The estimated average exposure to airborne 'total' dust was 22.5 mg m-3 (Permissible Limit of Exposure 1.08 mg m-3), and respirable dust 2.93 mg m-3 (PLE 0.36 mg m-3). This shows that 'total' dust exposure was 7.7 times higher than respirable dust. Since the present work systems and practices may pose a serious health risk to the workers, public and the environment, suitable preventive and control measures have been suggested for improvement in the workplace.

Occupational exposure to dust in slate pencil manufacture.

Slate pencils are manufactured from natural rock known as Binota Shale in small factories. Since the dust generated by stone-cutting and groove-making machines during the process contains a very high percentage of free silica and the particles are of sizes ranging up to a few microns in diameter the exposure both to respirable and to total inhalable airborne dust was assessed. Dust sizing revealed that all of the dust was respirable (less than 2.5 microns). Measurement of the intake velocity of the exhaust system in many cases showed it to be less than 10 m s-1. Suggestions are made for improvement in the working conditions.