RADIOPROTECTIVE EFFECT OF HYDROXYL RADICAL SCAVENGERS ON PROKARYOTIC AND EUKARYOTIC CELLS UNDER VARIOUS GAMMA IRRADIATION CONDITIONS

The influence of various hydroxyl radical scavengers such as methanol, ethanol and dimethyl sulfoxide on radiation sensitivity of prokaryotic cells (bacteria Escherichia coli) and eukaryotic cells (yeast Saccharomyces cerevisiae and V79 cells—Chinese hamster pulmonary fibroblasts) irradiated by 60Co gamma radiation was investigated. The dependence of radiation sensitivity on dose rate in range from 1.8 to 100 Gy h−1 was evaluated. Survival of cells irradiated by increasing dose rates was followed using clonogenic assay. Specific protective effect was found to be a nonmonotonous function of dose rate with typical maximum at the dose rate range from 50 to 55 Gy h−1 in all studied cell types.

Ozonation process intensification of p-nitrophenol by in situ separation of hydroxyl radical scavengers and microbubbles

The ozonation efficiency for removal of recalcitrant organic pollutants in alkaline wastewater is always low because of the presence of some hydroxyl radical scavengers. To solve this problem, the O3/Ca(OH)2 system was put forward, and p-nitrophenol (PNP) was chosen to explore the mechanism of this system. The effects of key operational parameters were studied respectively; the Ca(OH)2 dosage 3 g/L, ozone inlet flow rate 3.5 L/min, ozone concentration 65 mg/L, reactor pressure 0.25 MPa, and temperature 25 °C were obtained as the optimal operating conditions. After 60 min treatment, the organic matter mineralized completely, which was higher than the sum of the ozonation-alone process (55.63%) and the Ca(OH)2 process (3.53%). It suggests that the calcium hydroxide in the O3/Ca(OH)2 process possessed a paramount role in the removal of PNP. The liquid samples and the precipitated substances were analyzed by gas chromatography mass spectrometry, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy; it was demonstrated that Ca(OH)2 could accelerate the generation of hydroxyl radical and simultaneously in situ separate partial intermediate products and CO32− ions through some precipitation reactions.

Strategies for hydrogen peroxide dosing based on dissolved oxygen concentration for solar photo-Fenton treatment of complex wastewater

<div> <p>Hydrogen peroxide consumption is known to be one of the key parameters of the photo-Fenton process responsible for its high operating costs. The purpose of this study was to find out whether adding dissolved oxygen to the reaction medium in a continuous stream of pure oxygen or air with different H₂O₂ dosage strategies could improve the Dorfman mechanism, generating secondary oxidation species that could boost mineralization, and consequently, diminish H₂O₂ consumption. Experiments confirmed less efficient COD elimination. Additional DO slightly increased H₂O₂ consumption, as it initiated a series of reactions generating hydroxyl radical scavengers and H₂O₂ self-decomposition slowing down the reaction. At the same time, the study highlighted that automatic H₂O₂ dosing based on DO setpoints would be a highly attractive control option, however, more detailed studies on the initial amount of hydrogen peroxide and dosing rates must be undertaken.</p> </div> <p>&nbsp;</p>

A pilot scale comparison of advanced oxidation processes for estrogenic hormone removal from municipal wastewater effluent

This study investigates the oxidation of selected endocrine disrupting compounds (estrone, 17β-estradiol, estriol and 17α-ethinylestradiol) during ozonation and advanced oxidation of biologically treated municipal wastewater effluents in a pilot scale. Selected estrogenic substances were spiked in the treated wastewater at levels ranging from 1.65 to 3.59 μg · L−1. All estrogens were removed by ozonation by more than 99% at ozone doses ≥1.8 mg · L−1. At a dose of 4.4 · mg L−1 ozonation reduced concentrations of estrone, 17β-estradiol, estriol and 17α-ethinylestradiol by 99.8, 99.7, 99.9 and 99.7%, respectively. All tested advanced oxidation processes (AOPs) achieved high removal rates but they were slightly lower compared to ozonation. The lower removal rates for all tested advanced oxidation processes are caused by the presence of naturally occurring hydroxyl radical scavengers – carbonates and bicarbonates.