Document Type : Article
Authors
Dept. of Civil and Environmental Engineering Tarbiat Modares University
Abstract
A large amount of antibiotics consumed ends up in wastewater, in which they may exert selective pressure on or maintain resistance against microorganisms. Antibiotic resistant bacteria and genes encoding antibiotic resistance are commonly detected in wastewater, often at higher rates and concentrations compared to surface water. Wastewater can also provide favorable conditions for the growth of a diverse bacterial community, which constitutes a basis for the selection and spread of antibiotic resistance, including genetic resistance to
humans, livestock and poultry. Their elimination is very difficult by traditional biological treatment methods because they are hard biodegradable.
Oxy-tetracycline (OTC) is one of the famous tetracyclines that have environmental risk. Nano zero valent Iron (NZVI) particles can be a new suggestion for OTC remediation. In this study, 155 ppm of OTC by 1000 ppm
nano-scale zero valent iron with 200 W, UV-A radiation at pH of 3, were completely removed after 14 hours. The final products were carbon dioxide and water that were measured by a $CO_2$ analyzer. The iron compound on the surface of the nano zero valent Iron particles was Fe(OOH), which was determined by XRD analysis. Variations of parameter, including ORP, pH, and DO, during the removal process, were investigated for 6.5 hours. After 3 hours, the photocatalytic reaction by Fe(OOH) was started. The mechanism of OTC degradation was proposed by HPLC / ESI-MS and four by-products were obtained.
The kinetic models for by-products were first order, and the rate constants, by the first order kinetic model, were found to be equal to 0.0099, 0.0021, 0.0049 and 0.0074 min-1, respectively. The effect of competitive ions, including calcium $(Ca^2+)$, magnesium $(Mg^2+)$, chloride $(Cl^-)$, nitrate $(NO_3)$, sulfate
$(SO_4^2-)$ and bicarbonate $(HCO_3^-)$, with 10, 50, 100 and 200 ppm concentration, on OTC removal, were investigated. The results showed the negative effect of OTC removal by increasing the concentration of competitive ions, $NO_3^-$ $>$ $Ca^2+$ $approx$ $Mg^2+$ $>$ $Cl^-$ . But $SO_4^2-$ and $HCO_3^-$ had no considerable effect. The kinetic model for OTC removal in the presence of all competitive ion concentrations was first order, but, for 10 ppm of $NO_3^-$, $Ca^2+$ and $Mg^2+$, were pseudo first order.
Keywords
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