Photocatalytic degradation of caffeine by ZnO-ZnAl2O4 nanoparticles derived from LDH structure

Although antibiotics have been used in large quantities for some decades, until recently the existence of these substances in the environment has received little notice. It is only in recent years that a more complex investigation of antibiotic substances has been undertaken in order to permit an assessment of the environmental risks they may pose. Within the last decade an increasing number of studies covering antibiotic input, occurrence, fate and effects have been published, but there is still a lack of understanding and knowledge about antibiotics in the aquatic environment despite the numerous studies performed. This review addresses the present state of knowledge concerning the input, occurrence, fate and effects of antibiotics in the environment. It brings up important questions that are still open, and addresses some significant issues which must be tackled in the future for a better understanding of the behavior of antibiotics in the environment, as well as the risks associated with their occurrence. Questions related to resistance in the environment that may be caused by antibiotics will be addressed in the second part.

This review focuses on 118 pharmaceuticals, belonging to seventeen different therapeutic classes, detected in raw urban wastewater and effluent from an activated sludge system, a usual treatment adopted for urban wastewaters worldwide prior to final discharge into surface water bodies. Data pertaining to 244 conventional activated sludge systems and 20 membrane biological reactors are analysed and the observed ranges of variability of each selected compound in their influent and effluent reported, with particular reference to the substances detected most frequently and in higher concentrations. A snapshot of the ability of these systems to remove such compounds is provided by comparing their global removal efficiencies for each substance. Where possible, the study then evaluates the average daily mass load of the majority of detected pharmaceuticals exiting the secondary treatment step. The final part of the review provides an assessment of the environmental risk posed by their presence in the secondary effluent by means of the risk quotient that is the ratio between the average pharmaceutical concentration measured in the secondary effluent and the predicted no-effect concentration. Finally, mass load rankings of the compounds under review are compared with those based on their risk level. This analysis shows that the highest amounts discharged through secondary effluent pertain to one antihypertensive, and several beta-blockers and analgesics/anti-inflammatories, while the highest risk is posed by antibiotics and several psychiatric drugs and analgesics/anti-inflammatories. These results are reported with a view to aiding scientists and administrators in planning measures aiming to reduce the impact of treated urban wastewater discharge into surface water bodies. Copyright © 2012 Elsevier B.V. All rights reserved.