Selenium in wastewater: fast analysis method development and advanced oxidation treatment applications

Synthesis and characterization of titanium dioxide nanoparticles from Bacillus subtilis MTCC 8322 and its application for the removal of methylene blue and orange G dyes under UV light and visible light

Over the last decade there has been a huge increase in the green synthesis of nanoparticles. Moreover, there is a continuous increase in harnessing the potential of microorganisms for the development of efficient and biocompatible nanoparticles around the globe. In the present research work, investigators have synthesized TiO2 NPs by harnessing the potential of Bacillus subtilis MTCC 8322 (Gram-positive) bacteria. The formation and confirmation of the TiO2 NPs synthesized by bacteria were carried out by using UV-Vis spectroscopy, Fourier transforms infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX/EDS). The size of the synthesized TiO2 NPs was 80-120 nm which was spherical to irregular in shape as revealed by SEM. FTIR showed the characteristic bands of Ti-O in the range of 400-550 cm-1 and 924 cm-1 while the band at 2930 cm-1 confirmed the association of bacterial biomolecules with the synthesized TiO2 NPs. XRD showed two major peaks; 27.5° (rutile phase) and 45.6° (anatase phase) for the synthesized TiO2 NPs. Finally, the potential of the synthesized TiO2 NPs was assessed as an antibacterial agent and photocatalyst. The remediation of Methylene blue (MB) and Orange G (OG) dyes was carried out under UV- light and visible light for a contact time of 150-240 min respectively. The removal efficiency for 100 ppm MB dye was 25.75% and for OG dye was 72.24% under UV light, while in visible light, the maximum removal percentage for MB and OG dye was 98.85% and 80.43% respectively at 90 min. Moreover, a kinetic study and adsorption isotherm study were carried out for the removal of both dyes, where the pseudo-first-order for MB dye is 263.269 and 475554.176 mg/g for OG dye. The pseudo-second-order kinetics for MB and OG dye were 188.679 and 1666.667 mg/g respectively. In addition to this, the antibacterial activity of TiO2 NPs was assessed against Bacillus subtilis MTCC 8322 (Gram-positive) and Escherichia coli MTCC 8933 (Gram-negative) where the maximum zone of inhibition in Bacillus subtilis MTCC 8322 was about 12 mm, and for E. coli 16 mm.

Monoclonal antibody based immunoassay: An alternative way for aquatic environmental selenium detection

Environmental concerns about human health encouraged increasing methodological interest in selenium (Se), which is an essential non-metal trace element and varies within a narrow concentration range between essential and toxic. In this study, two types of long-armed Se haptens (Se-hapten-lc-NHS) were synthesized for the first time using active ester formalization. In producing monoclonal antibodies (mAbs), the derivatization of haptenized Se at para- (meta-) and ortho-sites showed different properties. Finally, a mAb derived from hybridoma 5A5² was confirmed to be capable of establishing an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA). There was a successful quantitative determination of Se⁴⁺ with a detection range of 17 to 207 pmol mL^-1 and a limit of detection of approximately 3.9 pmol mL^-1. The mAb was found to be remarkably sensitive and specific, with no evidence of cross-reactivity with other ions. The assay was validated for four kinds of Se forms in water samples and showed satisfactory recoveries between 80 % and 108 %, with coefficients of variation of 2.1 %-11 %. The method proposed in our study offers a useful protocol for the rapid screening of Se and provides an alternative solution for the analysis of Se in aquatic environments.

Trace Selenium Measurement in Water Using Laser-Induced Fluorescence Assisted by Laser Ablation

Selenium detection and removal from industrial and mining effluents have gained attention recently due to the negative effects of this trace element on aquatic life. However, the current methods for the detection of selenium in effluents are off-line by nature. In order to fill this gap, we investigated the use of laser ablation-assisted laser-induced fluorescence (LA-LIF) to measure trace amount of selenium in aqueous solutions. LA-LIF measurements are real time, label-free, standoff, and require no consumables as well as no sample preparation. They can provide a field-amenable, versatile tool for the measurement of selenium in the whole water treatment chain. We describe the system utilized, the temporal and fluence optimization studies, and the resulting calibration curve, which is linear over a wide dynamic range from parts-per-billion to tens of parts-per-million concentration levels. We also show that the achieved limit of detection of selenium can reach 32 µg/L using LA-LIF, without any kind of preconcentration or matrix transfer.

A microwave irradiation-persulfate-formate system for achieving the detoxification and alkali-activated composite geopolymerization of the chromate-contaminated soil

A microwave (MA) irradiation-persulfate-formate system was constructed to detoxify Cr contamination and solidify the geopolymerization of the alkali-activated composite material. Three series of experiments were correspondingly conducted to evaluate the treatment for the chromate-contaminated soil. The changes in the molar ratios of formate to persulfate and the mass rates of fortifier to soil led to a significantly greater reduction of Cr^VI in the detoxification experiments. The increase of blast furnace slag from 50% to 80% in the composite cementitious materials (CCM) intensified the immobilization efficiencies of chromate and the compressive strengths of geopolymer blocks. MA irradiation potentially enhanced the binding of Ca cations to the aluminosilicate compounds. The degree of reaction in the phenomenological kinetics model mathematically verified the geopolymerization process. Ettringite was formed within the structure of the geopolymer in the coupling system. Sulfate radicals released from persulfate not only contributed to the detoxification process but also strengthened the immobilization process.

Trivalent iron-tartaric acid metal-organic framework for catalytic ozonation of succinonitrile

As porous crystal materials, metal-organic frameworks (MOFs) have attracted wide attention in the field of environmental remediation. In this study, a trivalent iron-tartaric acid metal-organic framework (T2-MOF) was successfully synthesized using the inexpensive raw materials ferric chloride (FeCl₃.6H₂O) and tartaric acid (C₄H₆O₆). The physical and chemical properties of T2-MOF were studied by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller. After that, T2-MOF was used as a catalyst for catalytic ozonation of succinonitrile. The results show that T2-MOF has obvious crystal characteristics and uniform structure. In addition, T2-MOF exhibits strong catalytic performance in ozonation of succinonitrile. The results indicate that the chemical oxygen demand (COD) removal rate is affected by various operating parameters including catalyst characteristics dosages and initial pH values. In the ozonation with 30 mg L^-1 T2-MOF, the COD removal rate of 100 mg L^-1 succinonitrile reached 73.1% (±4.6%) within 180 min, which was 67.3% (±4.4%) higher than that obtained in the process without catalyst. T2-MOF maintained strong catalytic performance with the pH range of 3.0-7.0. By monitoring the Fe²⁺ concentration at different reaction time, it was found that the homogeneous catalysis occurred simultaneously with the heterogeneous catalysis.