Recirculation of powdered activated carbon improves the adsorption of organic micropollutants in membrane hybrid processes

Abstract In this pilot study, we investigated how the counter-current of powdered activated carbon (PAC) improved the removal of organic micropollutants in two membrane hybrid processes. Comparing an inline-dosing process with fine or conventional PAC with a state-of-the-art contact reactor process that uses conventionally sized PAC. Recirculation of partially loaded fine PAC from the inline-dosing membrane hybrid process to the upstream biological treatment reduced the necessary carbon dosage to meet EU requirements for organic micropollutant removal from 1.4 mg PAC /mg DOC down to 0.7 mg PAC /mg DOC . Therefore, the counter-current flow reduced the carbon demand of the inline-dosing process by 50%. At the same time, the fine PAC inline-dosing process reached an even lower carbon demand than the reference process, which required dosages of 1.0 mg PAC /mg DOC . We also determined where and at what timescale adsorption takes place with and without PAC recirculation. The reduction of micropollutants in PAC counter-current schemes is shifting toward the activated sludge process. In this study, we demonstrated the relevance of process configuration as compared to material selection, and particularly the importance of recirculation of PAC in real applications. We also proposed a way to transfer previous lab- or pilot-scale results (without PAC recirculation) to real applications with PAC recirculation.