Degradation of oxytetracycline by ferrate(VI): Treatment optimization, UHPLC-MS/MS and toxicological studies of the degradation products, and impact of urea and creatinine on the removal

Abstract

The degradation of oxytetracycline (OTC) by ferrate(VI) for its application in wastewater treatment was investigated. The degradation conditions such as pH, reaction time, and molar ratio of ferrate(VI) to OTC were optimized by central composite design and response surface methodology. The most efficient, 90 % removal of OTC was obtained at pH 3, molar ratio ferrate(VI)/OTC of 3, and reaction time of 60 s. In the first step, demethylation, deamidation, and hydroxylation derivatives of OTC were formed. The end-products of the OTC degradation were hydroxyaliphatic amines and phenolic compounds formed from ring scission in the tetracene moiety of OTC. The end-products were not toxic to both bacteria (MARA and Microtox®) and protozoa (Spirotox) tests. Urea and creatinine are the major nitrogenous end-products of human metabolism occurring in municipal wastewater. Therefore, the impact of creatinine and urea on removal of OTC was also investigated. The presence of creatinine at investigated molar ratios of 1:1 and 1:2 did not affect the removal of OTC by ferrate(VI). The removal of OTC was 90 % after 60 s. However, after 60 s, in the presence of urea at molar ratio OTC/urea 1:1, removal efficiency was reduced from 90 to 80 %, whereas, at higher molar ratio of 1:2, the efficiency was 90 %. It may be explained by the formation of urea radicals that may facilitate the degradation of OTC by ferrate(VI) and its degradation products. The urea radicals may also induce formation of more reactive ferrate(V) or ferrate(IV) species. The ferrate was also applied to remove OTC from treated wastewater. Overall study results have shown thatferrate(VI) has a good potential for use in removal of tetracycline antibiotics from wastewater.