Trends in organic micropollutants removal in secondary treatment of sewage

Organic micropollutants (OMPs) comprise a wide group of substances highly consumed in modern societies. There has been a growing social and scientific interest on OMPs in wastewaters in the twentyfirst century. This research paper has identified the evolution of the research trends in the period 2001–2017 on OMPs fate during secondary wastewater treatment. These trends have moved from a global perspective on the occurrence of OMPs in wastewaters to more specific research focussed on understanding their behaviour during advanced treatment processes. Based on a bibliometric analysis carried out using one of the leading scientific databases, pharmaceuticals have been identified as the main group of OMPs. An increasing number of publications have been released on the fate of pharmaceuticals in wastewater with a growing number of countries involved: from 38 publications belonging to 14 countries in first 5-year period analysed (2001–2005) up to 138 from 42 countries only in the last 2 years (2016–2017). The main operational conditions in wastewater treatment plants influencing the removal of OMPs, as well as the mechanisms involved depending on the physico-chemical characteristics of the substances are reviewed. The paper also considers the role of microbial populations, as well as technological and operational features in OMPs abatement. Finally, a specific section is dedicated to the metabolic and cometabolic biotransformations of some OMPs taking place under heterotrophic, nitrifying and anaerobic conditions, a more novel research trend explored more recently.