Treatment of pharmaceuticals by PAC: case study of a full-scale pilot at Seine Centre WWTP.

International audienceThe micropollutants fate in the environment has become an increasing topic of interest last decades, especially in heavily urbanized area. In addition to priority pollutants (WFD), a large number of molecules such as pesticides, personal care products, pharmaceuticals, flame retardants, artificial sweeteners, etc. is detected in the environment and also represents a potential threat for it (Rogers 1996, Jørgensen and Halling-Sørensen 2000, Heberer 2002). Furthermore, the fate of pollutants within the wastewater treatment plants (WWTP) is today well studied and WWTP effluents are generally considered as an important source of contamination for a long time, especially in the case of urban areas (Heberer 2002). Tertiary treatments are nowadays developed because some molecules are persistent to primary and biological treatments. Different kinds of technologies already exist and are mainly imported from drinking water industry. Adsorption on activated carbon seems to be one of the most interesting of these processes regarding its simplicity, efficiency and functioning costs. Some recent papers have already shown its efficiency over persistent micropollutants (Margot et al. 2013; Boehler et al. 2012). In this context, the LEESU (Water, Environment and Urban Systems Laboratory), through the framework of the OPUR (Observatory of Urban Pollutants) research programme and in close partnership with the Parisian public company (SIAAP) which manages wastewaters of the 8 million inhabitant conurbation, launched this study on the tertiary treatments. Thus, a full-scale activated carbon adsorption pilot (50 m3/h) has been set up at the Seine Centre WWTP (capacity of 250 000 m3/day) and is currently studied in order to i) characterize the efficiency of the process for priority and emerging pollutants removal and ii) characterize the sorption mechanism and the different parameters influencing it (organic matter competition, operating parameters, activated carbon structure and properties, etc.). The process consists in a fluidized bed of powdered activated carbon (PAC) reactor. As coagulant and flocculant are added to the system, the bed stays steady and no filtration system is needed to separate water and PAC. In addition, a new type of activated carbon, developed for the process, will also be tested. These micro-grains have an intermediary size (300 - 400 µm) compared to powder ( 1 mm), what should allow a high efficiency together with a higher ease of operating for the process as no chemicals are needed and solid retention time can be higher. Furthermore, the micro-grain selected for this study is regenerated and can easily be recycled, what is consistent with an environmental application. In fact, a recycling by the supplier system can be implemented, potentially resulting in cost reductions and in avoiding the waste carbon handling issue. Considering this, the selection of the process configuration (PAC or micro-grain) will then be possible depending on each site situation and treatment requirements. The study is organized in 3 phases. The first phase consists in an optimization of the pilot, where different configurations (PAC dose, hydraulic retention time and nature of carbon) are tested, while the second phase will operate at steady state. Finally, the third phase will allow testing the micro-grain configuration. A strategy of intensive (every 2 weeks during 2 years) and large (> 130 molecules) screening campaigns has been built to get a very large database and range of information, by measuring inlet and outlet concentrations of pharmaceuticals, pesticides, priority substances and metals during a total of 30 campaigns. Preliminary results tend to highlight a removal of 15-50% of dissolved organic carbon (DOC) and a slight decrease of nitrogenous pollution (10-30%) whereas TSS are not eliminated. Regarding micropollutants, only pharmaceuticals results are currently available. A significant removal (40-90%) of these molecules seems possible even for the most hydrophilic (log KOW < 4) ones such as antibiotics and beta-blockers. Moreover, a clear influence of the operating parameters can be highlighted. This is in good accordance with recent and similar works in Switzerland and Germany (Margot et al. 2013; Boehler et al. 2012). In addition, a significant relation between micropollutant, DOC and UV-254 signal removals seems to exist, and the potential of using measure of UV-254 as a control tool of the efficiency of the process will be evaluated. This presentation aims at presenting results from the two PAC phases and the first feedbacks from the micro-grain phase. A focus will be done on micropollutants fate, but classical wastewater treatment parameters will also be presented to have a precise and complete overview of the potential impact of the addition of a tertiary treatment to the urban areas WWTPs