Semi-quantitative analysis of a specific database on priority and emerging substances in wastewater and sludge

The Water Framework Directive (WFD) has drawn attention to a series of metals and organic compounds because of their demonstrated or potential harmfulness for aquatic environments. The aim of our work was to build and to process a "practical" database focused on the role of wastewater treatment plants for the removal of the 37 priority compounds that have to be reduced or stopped by 2015, and of 34 additional relevant contaminants. About 11,000 concentration values in raw and treated wastewater and sludge, from more than 100 peer-reviewed articles and six French national screening programs, were integrated. A systematic approach showed the global low quality of data for most of the compounds, with missing information about the treatment process, sampling and analysis, leading to 10% of the data available for removal efficiency calculations. A semi-quantitative analysis allowed the identification of 20 priority and 10 additional relevant substances more frequently quantified at significant concentrations in raw wastewater and treated wastewater. Conventional activated sludge was able to remove more than 70% of half of the studied compounds, leaving only 10% of them with less than 50% removal. Physical-chemical treatments appeared to be about 30% less efficient than biological treatments. In addition, very few data are available concerning some compounds and some processes, especially sludge treatment and tertiary wastewater treatment processes. Therefore, complementary on-site measurements and modeling are required to propose adapted solutions for the treatment of priority and emerging substances in wastewater treatment plants.