Use of passive samplers (POCIS and SPMD) for the evaluation of the efficiency of wastewater tertiary treatments

Our objective is to study some advanced processes, such as ozonation (O3) or Granular Activated Carbon (GAC) as example, used in tertiary stage of wastewater treatment plants (WWTP). The challenges when studying such processes is to be able to measure organic micropollutants at very low concentrations (ng/L). To achieve this goal, passive samplers (PS) like POCIS (Polar Organic Chemical Integrative Sampler) and SPMD (Semi-Permeable Membrane Device) were used. The results of chemical analyses on PS were compared with those on grab water samples. Four one-month-long sampling campaigns were carried out in 3 different WWTP: 1) O3 (full-scale) followed by GAC (pilot) in WWTP A, 2) O3 only (full-scale) in the same WWTP A, 3) GAC (pilot) in WWTP B, 4) polishing pond (full-scale) in WWTP C. In all campaigns, POCIS were exposed in water during 14 days and SPMD during 28 days. To be able to compare these 4 campaigns and the molecule concentrations upstream and downstream the tertiary treatment, POCIS and SPMD were always immersed in an aquarium in the same controlled experimental conditions of flow (280 mL/min), temperature (20° C) and light. To insure quality of data, POCIS and SPMD were exposed in triplicate and field blanks were realized (i.e. PS exposed to the ambient air). In parallel, 2h composite water samples were collected at D0, D14 and D28. Targeted chemical analyses were performed on POCIS extracts for 117 hydrophilic compounds belonging to pharmaceutical, hormone, pesticide and alkylphenol classes and on SPMD extracts for 46 lipophilic compounds belonging to chlorine pesticides, Polycyclic Aromatic Hydrocarbon, PolyChloroBiphenyl, PolyBrominated DiphenylEthers classes. Hydrophilic compounds and PAH were also analysed in water samples. We will present results obtained for SPMD and POCIS. As an example, compared to grab sampling, POCIS allowed detecting 7 more pharmaceuticals in influent of tertiary treatments and 4 more in effluents in the 2 first sampling campaigns. Nevertheless, information on process efficiency is the same since the decrease of pharmaceutical concentrations after advanced water treatment is in the same order of magnitude with grab and passive sampling in the 2 first sampling campaigns. Hence, POCIS appears as an interesting tool to characterize tertiary stages of WWTPs with analysis of organic micropollutants at very low concentrations.