The presence of pharmaceutical residues in fresh water bodies has been of significant environmental concern due to their undesirable effects on aquatic organisms even at very low concentrations. The present study is about the elimination and overall degradation of a common anti-inflammatory pharmaceutical-paracetamol in water by catalytic oxidation using high-frequency ultrasound, UV-irradiation and both. The catalysts were synthesized sonolytically by immobilization of Pd, Au and both on commercial TiO 2 (P-25) to produce very fine nanoparticles with excellent surface porosity. It was found that immobilization of precious metals was an effective means of enhancing the catalytic activity of TiO 2 in the presence of ultrasound and UV-irradiation, but sonication was more effective than photolysis for the activation of Pd-TiO 2 and Pd/Au-TiO 2 , owing to their smaller particle size (than that of Au-TiO 2 ) that facilitated the formation of cavitation bubbles and reactive species on the catalysts. Moreover, Pd-TiO 2 was the most stable nanocomposite in terms of recovery and reuse (in sonocatalysis), exhibiting closely the same degree of catalytic activity as that in the previous use within very short time. No difference was observed between sonolysis and photolysis when using commercial TiO 2 , due to the slight turbidity of the solution and the competion for photons arising from photoreactivity of PCT. Application of sonolysis and photolysis simultaneously resulted in enhanced rate of PCT elimination and TOC decay in the presence of all catalysts. However, synergistic enhancements were observed only with Pd/Au-TiO 2 and Au-TiO 2 during oxidation and mineralization of the compound, respectively. Enhanced activity of Au-TiO 2 for the longer mineralization process was attributed to complete elimination of PCT (reduced photon competition) and the individual activity of gold in the UV-vis region.

Pharmaceuticals and personal care products (PPCPs) are those substances used for medical care, cosmetics, hygiene and health care purposes. Due to their globally high production and consumption rates and rapid discharge into the environment without control, they are of considerable public concern. Many of them, particularly antibiotics, analgesics, endocrine disruptors and microbial/disinfecting substances are frequently detected in wastewater treatment effluents, fresh water systems and groundwater in concentrations ranging from ng L−1 to mg L−1. Moreover, most of them are persistent and tend to bioaccumulate in cell tissue, being transported subsequently to vegetables, crops and drinking water sources. As such, a large group of PPCPs are recognized with their potential to impair the ecosystem and/or to induce health risks, so that they have been classified under “emerging contaminants.” The present study is a comprehensive review of the literature on the occurrence, fate and potential environmental and health risks of PPCPs in the aquatic and terrestrial environments. It also encompasses the reported cases of human health disorders or risks, although the data so far is inadequate for presenting a complete assessment. Finally, the study covers a short review of the most promising advanced technologies for their partial or ultimate elimination from wastewater treatment effluents and water.

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The study is the assessment of commercial γ-AlO and its sonolytically modified nanocomposite in catalytic ozonation of paracetamol (PCT), which is an emerging water contaminant and a highly reactive compound with ozone. The results showed that commercial alumina was ineffective regardless of the solution pH, due to the low affinity of the catalyst surface for PCT and the high reactivity of the solute with molecular ozone. The modified catalyst, which was synthesized by decoration of the original surface with nanoparticles of platinum provided considerable improvement in the performance of the catalyst, particularly in mineralization of the target compound. The presence of OH scavenging agents in solution markedly retarded the rate of PCT oxidation and organic carbon decay, to signal the importance of radical-mediated reaction mechanisms on the degradation of the compound. Finally, the attempt to accelerate the reactions by running them in the presence of ultrasound was found inadequate for the early oxidation, but highly adequate for the longer mineralization process. The failure was attributed to the diffusion of a large fraction of ozone into the gaseous cavity bubbles (reduced probability of direct reactions) and the extreme conditions of cavitation collapse that partially damaged the catalyst surface. The success (in mineralization) was explained by the shift of the reaction site from the bulk solution (poor adsorption on catalyst surfaces) to the solid surface and the gaseous cavity bubbles (via enhanced hydrophobicity), both being considerably more active reaction media.

Advanced oxidation processes (AOPs) are based on the in situ production of hydroxyl radicals (•OH) and reactive oxygen species (ROS) in water upon irradiation of the sample by UV light, ultrasound, electromagnetic radiation, and/or the addition of ozone or a semiconductor. Diclofenac (DCF), one of the emerging organic contaminants (EOC), is of environmental concern due to its abundancy in water and is known to be subjected to AOPs. The current study uses density functional theory (DFT) to elucidate the mechanisms of the reactions between •OH and DCF leading to degradation by-products, P1-P9. The initial encounter of DCF with •OH is proposed to lead to either the abstraction of a hydrogen or the addition of the hydroxyl radical to the molecule. The results showed that OH addition radicals (R ) are both kinetically and thermodynamically favored over H abstraction radicals (R). The intermediate radicals give degradation by-products by subsequent reactions. The by-products P7 and P8 are easily formed in agreement with experimental findings. Finally, acute toxicities at three trophic levels are estimated with the Ecological Structure Activity Relationships program. DCF and most of the by-products were found to be harmful to aquatic organisms, P9 being the only by-product that is not harmful at all three trophic levels.

The study is about the assessment of single and multi-frequency operations for the overall degradation of a widely consumed analgesic pharmaceutical-ibuprofen (IBP). The selected frequencies were in the range of 20-1130kHz emissions coming from probes, baths and piezo-electric transducers attached to plate-type devices. Multi-frequency operations were applied either simultaneously as "duals", or sequentially at fixed time intervals; and the total reaction time in all operations was 30-min. The work also covers evaluation of the effect of zero-valent iron (ZVI) on the efficiency of the degradation process and the performance of the reaction systems. It was found that low-frequency probe type devices especially at 20kHz were ineffective when applied singly and without ZVI, and relatively more effective in combined-frequency operations in the presence of ZVI. The power efficiencies of the reactors and/or reaction systems showed that 20-kHz probe was considerably more energy intensive than all others, and was therefore not used in multi-frequency operations. The most efficient reactor in terms of power consumption was the bath (200kHz), which however provided insufficient mineralization of the test chemical. The highest percentage of TOC decay (37%) was obtained in a dual-frequency operation (40/572kHz) with ZVI, in which the energy consumption was neither low nor exceptionally too high. A sequential operation (40+200kHz) in that respect was more efficient, because it required much less energy for a similar TOC decay performance (30%). In general, the degradation of IBP increased with increased power consumption, which in turn reduced the sonochemical yield. The study also showed that advanced Fenton reactions with ZVI were faster in the presence of ultrasound, and the metal was very effective in improving the performance of low-frequency operations.

The study consists of a detailed investigation of the degradability of the emerging water contaminant-caffeine by homogeneous and heterogeneous Advanced Oxidation Processes (AOP’s), estimation of a synergy index for each hybrid operation thereof, and proposing the most plausible reaction mechanisms that are consistent with the experimental data. It also encompasses evaluation of the effect of the water matrix represented by carbonate species and humic acids, as strong scavengers of hydroxyl radicals. The results showed that single AOP’s such as sonolysis (577 kHz) and photolysis with H 2 O 2 provided complete caffeine elimination, but they were insufficient for the mineralization of the compound. Hybrid AOP’s were considerably more effective, particularly when operated at a heterogeneous mode using commercial TiO 2 . The most effective hybrid process was UV-H 2 O 2 /TiO 2 , which provided more than 75% TOC decay at the minimum test doses of the reagent and catalyst. While the addition of ultrasound to the process significantly increased the rate of caffeine decomposition, it reduced the overall degradation of the compound to 64% in terms of TOC decay. The antagonistic effect was attributed to the formation of excess H 2 O 2 , and the presence of cavity clouds and/or high density layers that inhibited the transmission of UV light. The effect of natural water ingredients was found to reduce the reaction rates, signifying the major contribution of hydroxyl radicals to the destruction of caffeine. The proposed reaction mechanisms based on OH radical attack and the calculated energy barriers were in good agreement with the experimentally detected reaction byproducts.