The extensive production and usage of antibiotics have led to an increasing occurrence of antibiotic residuals in various aquatic compartments, presenting a significant threat to both ecosystem and human health. This study investigated the degradation of selected β-lactam antibiotics (penicillins: ampicillin, penicillin V, and piperacillin; cephalosporin: cephalothin) by UV-254nm activated H2O2 and S2O8(2-) photochemical processes. The UV irradiation alone resulted in various degrees of direct photolysis of the antibiotics; while the addition of the oxidants improved significantly the removal efficiency. The steady-state radical concentrations were estimated, revealing a non-negligible contribution of hydroxyl radicals in the UV/S2O8(2-) system. Mineralization of the β-lactams could be achieved at high UV fluence, with a slow formation of SO4(2-) and a much lower elimination of total organic carbon (TOC). The transformation mechanisms were also investigated showing the main reaction pathways of hydroxylation (+16Da) at the aromatic ring and/or the sulfur atom, hydrolysis (+18Da) at the β-lactam ring and decarboxylation (-44Da) for the three penicillins. Oxidation of amine group was also observed for ampicillin. This study suggests that UV/H2O2 and UV/S2O8(2-) advanced oxidation processes (AOPs) are capable of degrading β-lactam antibiotics decreasing consequently the antibiotic activity of treated waters.

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The presence of pathogenic antibiotic-resistant bacteria in aquatic environments has become a health threat in the last few years. Their presence has increased due to the presence of antibiotics in wastewater effluents, which are not efficiently removed by conventional wastewater treatments. As a result there is a need to study the possible ways of removal of the mixtures of antibiotics present in wastewater effluents and the antibiotic-resistant bacteria, which may also spread the antibiotic resistance genes to other bacterial populations. In this study the degradation of a mixture of antibiotics i.e. sulfamethoxazole and clarithromycin, the disinfection of total enterococci and the removal of those resistant to: a) sulfamethoxazole, b) clarithromycin and c) to both antibiotics have been examined, along with the toxicity of the whole effluent mixture after treatment to the luminescent aquatic bacterium Vibrio fischeri. Solar Fenton treatment (natural solar driven oxidation) using Fenton reagent doses of 50 mg L(-1) of hydrogen peroxide and 5 mg L(-1) of Fe(3+) in a pilot-scale compound parabolic collector plant was used to examine the disinfection and antibiotic resistance removal efficiency in different aqueous matrices, namely distilled water, simulated and real wastewater effluents. There was a faster complete removal of enterococci and of antibiotics in all aqueous matrices by applying solar Fenton when compared to photolytic treatment of the matrices. Sulfamethoxazole was more efficiently degraded than clarithromycin in all three aqueous matrices (95% removal of sulfamethoxazole and 70% removal of clarithromycin in real wastewater). The antibiotic resistance of enterococci towards both antibiotics exhibited a 5-log reduction with solar Fenton in real wastewater effluent. Also after solar Fenton treatment, there were 10 times more antibiotic-resistant enterococci in the presence of sulfamethoxazole than in the presence of clarithromycin. Finally, the toxicity of the treated wastewater to V. fischeri remained very low throughout the treatment time.

Continuous degradation of an abiotic part of an environment as well as disruption of the homeostatic state of biota can be attributed to the increasing rate of human impact on the environment. An idea about the diversity of pollutants that can potentially appear in the environment can be gained by monitoring the amount of already existing chemicals and the rate of appearance of new ones. If a compound is known and in use it seems obvious that in the end it will be introduced into the environment. Figure 1.1 shows a classification of environmental pollutants. Analysts have concentrated mainly on: Non-identified pollutants-pollutants that exist in the environment for a long time but due either to lack of proper analytical procedures, insufficient development of analytical devices, or lack of new methodological parameters have not yet been identified.

Water deprivation with regard to quantity and quality is one of the most important environmental problems of the century. The increasing demand of water resources puts pressure on the utilization of alternative sources such as treated wastewater. In the context of "reduce, reuse, and recycle," the inclusion of treated wastewater in the water cycle seems a promising practice for water management. The lack of general acceptance of stakeholders and public, however, still hinders the widespread application of wastewater reuse. A reason for this is, among others, the presence of contaminants of emerging concern in treated wastewater. This has led to an increased concern about direct and indirect effects to the environment and possible implications to human health. The development and application of bioassays able to identify and quantify the biological potency of treated wastewater is an ongoing research effort, especially when taking into consideration that a plethora of contaminants exist and interact in this complex matrix. This chapter summarizes available literature regarding the sensitivity of currently applied bioassays for assessing biological effects of treated wastewater and their correlation with chemical analysis. The focus is on pharmaceuticals since they represent one of the major groups of contaminants of emerging concern with many unanswered questions currently in place.

This special issue contains original research articles on solar energy use for green applications. In particular, the use of solar thermal energy for low environmental impact processes or the use of the light (with or without heterogeneous photocatalysts) for environmental remediation or synthesis was considered. The topic is highly challenging and the subject would be important, timely, and of great interest. Among the submitted manuscripts, 5 were selected as suitable for publication through the strict experts' peer reviews. The papers to be published in this special issue are "Design and Performance Evaluation of a Solar Assisted Heat Pump Dryer Integrated with Biomass Furnace for Red Chilli" for the direct solar light/thermal applications; "Sorbents Coupled to Solar Light TiO 2-Based Photocatalysts for Olive Mill Wastewater Treatment," "Photodegradation of 2,4-Dichlorophenol in Aqueous Systems under Simulated and Natural Sunlight," and "Flexible Bench-Scale Recirculating Flow CPC Photoreactor for Solar Photocatalytic Degradation of Methylene Blue Using Removable TiO 2 Immobilized on PET Sheets" for the photodegradation topic; and "Noble Metal Decoration and Presulfation on TiO 2 : Increased Photocatalytic Activity and Efficient Esterification of n-Butanol with Citric Acid" for synthetic photochemistry. We believe that this special issue can be interesting and inspiring for the readers of the journal since this advanced interdisciplinary technology involves a wide range of subjects.