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Removal of micropollutants with activated sludge : proposition of a new kinetic model and special focus on hydrodynamic reactor configuration and local mixing

Abstract : One of the main challenges currently facing environmental conservation is to reduce the discharge of micropollutants (MPs) from wastewater treatment plants outflows (WWTPs). Biological aerobic processes are the most commonly used treatment, but conventional systems were not conceived with the objective of eliminating micropollutants (MPs). In this work, the removal enhancement of seven micropollutants compounds (pharmaceuticals and industrial chemical) which cover various degree of biodegradability was studied using activated sludge process. To achieve this goal, an experimental methodology followed by a simulation strategy were developed. The systematic study of the impact of WWTPs operational parameters, such as sludge retention time (SRT), hydraulic retention time (HRT) and biomass concentration (CTSS), on the MPs removal was experimentally quantified in nine Sequencing Batch Reactor (SBR) setups. The enhancement of the SRT increased the removal of all the MPs except for two macrolides antibiotics. Application of a higher HRT did also improve MPs removal as could be expected from the measured removal rate constants. More interestingly, our results indicated that, contrary to what is postulated, the removal rate of micropollutants is not proportional to biomass concentration, especially for high ones. Compared to removal rates at 3 to 5 gTSS L- 1 of biomass, an additional increase at 8 gTSS L-1 produced only an unexpected moderate effect. New kinetics of the power law have been studied to cover the full range of biomass concentration conditions in activated sludge systems. It takes into account the limitation of the transport of micropollutants to biomass when its concentration is high. In this case, it has also been shown that the transport of micropollutants is based on molecular diffusion. This process has been added to the proposed kinetic equation. A simulation program of a wastewater treatment plant (SBR and continuous) has been developed. The numerical results using the new kinetics corresponded well to the experimental results. The simulations showed that, on the one hand, the improvement of the local mixing of the mixture greatly favors the elimination, on the other hand, the tiering of the reactor configuration by giving it a hydrodynamic close to a very large cascade of reactors also contributes to greatly improve the elimination of MPs. This can be achieved by building baffle reactors with a width of 2 m and an extended length of more than 200 m. Finally, the combination of these two local and global processes makes it possible to considerably increase the elimination of moderately and slowly biodegradable MPs.
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Submitted on : Thursday, June 25, 2020 - 10:51:03 AM
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  • HAL Id : tel-02880680, version 1



Rana Hatoum. Removal of micropollutants with activated sludge : proposition of a new kinetic model and special focus on hydrodynamic reactor configuration and local mixing. Chemical and Process Engineering. Université de Lorraine, 2019. English. ⟨NNT : 2019LORR0331⟩. ⟨tel-02880680⟩



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