Abstract
The transformation products (TPs) of water contaminants generated during wastewater treatment can sometimes be equally or even more hazardous than the parent compounds. Therefore, for a comprehensive assessment of removal efficiency of a water treatment technology, it is mandatory to monitor not only the pollutants but also of their TPs. However, this type of evaluation studies is lacking in the case of water combined treatments. In this study, the elimination of metoprolol (MTP), metoprolol acid (MTPA) and the TPs generated was evaluated in pure water and hospital wastewater (HWW) using UV/H2O2 before and after fungal (FG) or conventional activated sludge (CAS). The major transformation pathways were suggested in terms of transformation of the parent compounds through bio-transformation and photo-transformation mechanisms. The results reveal an extended removal of MTP, MTPA and TPs after UV/H2O2 single experiment treating spiked pure water at 2.5 mg/L, without increasing the treated effluents toxicity. However, combined treatments were required to achieve similar removal percentages in spiked real HWW at 2.0 µg/L: while AOPs combined with FG exhibited lower removal efficiencies with generation of persistent intermediates (such as α-HMTP and TP240), AOPs combined with CAS attained the higher persistent TPs removal. In particular, AOP + CAS was classified as the most effective combination for HWW with the highest removal of the parent compounds (86% for MTP and 100% for MTPA), of the intermediates generated (up to 85%) and with a low presence of toxic TPs (such as O-DMTP). This study demonstrates that comprehensive evaluation of the intermediates generated along water treatment technologies is highly recommended to successfully evaluate their removal efficiencies.
Highlights
The occurrence of pharmaceutical active compounds (PhACs) and their metabolites in water bodies has become an imperative concern due to their potential impact on both environment and human health [1,2,3]
In the case of Conventional activated sludge treatments (CAS), MTP biodegradation resulted in the generation of metoprolol acid (MTPA), which was the major generated intermediate, and in some cases classified as persistent [44,51]. α-HMTP was both reported as human metabolite, generated after pharmaceutical consumption, and transformation products (TPs) in biological treatments [44,51]. α-HMTP is usually persistent, it was detected in influent wastewater treatment plants (WWTPs), and it may be classified of important concern [17,44]
The binding of the hydroxyl radical in the MTP aromatic ring may lead to the formation of TP284, which is further oxidized to TP300 and TP316 [66]
Summary
The occurrence of pharmaceutical active compounds (PhACs) and their metabolites in water bodies has become an imperative concern due to their potential impact on both environment and human health [1,2,3]. Hospital wastewater (HWW) has been identified as responsible for introducing high loads of contaminants with potentially toxic effects in aquatic ecosystems [5]. The incomplete elimination of the persistent pollutants in centralized conventional municipal wastewater treatment plants (WWTPs) allows the release of these contaminants into the environment [1,6]. In this sense, dedicated on-site wastewater treatment of HWW has been widely recommended by several authors [5,7]. Specific directives or guidelines in Europe for the management of hospital effluents are missing and the implementation of full-scale HWW treatment has been introduced only in few cases [5,8]. The use of tailored and dedicated treatment technologies could stir up HWW decentralized treatment
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