Removal of Micropollutants from Secondary Effluents and Sludge by Various Processes in Rural and Peri-urban Areas

The present work details the results of a comprehensive study dealing with the fate of several families of micropollutants (with various physicochemical properties) through tertiary treatment processes of water and through sludge treatments. Powerful and sensitive analytical techniques were used: 16 metals and 39 organics (pharmaceuticals, polycyclic aromatic hydrocarbons, alkylphenols, pesticides) were analysed in wastewaters; 14 metals and 62 organic hydrophobic micropollutants were measured in sludge (estrogenic hormones, polychlorinated byphenyl, polybrominated diphenyl ethers, polycyclic aromatic hydrocarbons, alkylphenols and other organics). We studied treatment processes adapted for rural areas involving low energy-consumption: trench system, polishing pond, horizontal subsurface flow constructed wetlands with various adsorbing materials (i.e. expanded clay, zeolite, activated carbon, apatite, gravels) running at tertiary stage of water treatment; and sludge drying reed-bed operated at two different resting periods. Our results show that the trench system was not efficient for additional removal of refractory micropollutants. The polishing pond had higher removal efficiencies (between 30 and 70%) for some pharmaceuticals due to indirect photodegradation. The horizontal subsurface flow constructed wetland (HSSF-CW) built with activated carbon showed almost full-removal during more than 330 days for pharmaceuticals, pesticides, several metals and nonylphenoxyacetic acid. For the HSSF-CWs built with expanded clay or zeolite, we obtained removal efficiencies of 70% for half of studied pharmaceuticals and alkylphenols mono- and di-ethoxylates. The removal efficiencies of other substances were much lower than the ones measured with activated carbon, but they were still higher than the ones measured with gravel (filter designed for denitrification) or apatite (designed for phosphorus removal). Due to better oxygen conditions, the sludge drying reed-bed with low frequency of sludge input resulted in better removal for organic micropollutants than the sludge drying reed-bed with high frequency of sludge input.