Mastering granular activated carbon filtration to remove organic micropollutants, antibiotic resistance and metals for municipal wastewater reuse

GAC filtration of municipal wastewater was optimized and intensified, making its implementation and operation directly after secondary clarification possible and relevant. GAC was first selected based on laboratory tests. Performances on organic micropollutants were linked to the repartition of BET surface between micropores and meso/macropores. At pilot scale, in order to limit the impact of head loss, downflow declogging sequences (DCS) were implemented and upflow filtration tested. 6 to 12 DCS per day led to a 4.7-5.5-fold increase of particles retention capacity between backwashes (cycle duration of 20-120 h), and upflow operations improved head loss evolution profile with only a slight GAC (<15 %) expansion. DCS allows backwash frequency reduction, enabling significant water savings. Both adaptations maintained high organic micropollutants removals compared to a review of 16 GAC studies at pilot or full-scale, results being in the upper range. A specific dose of 2.0-2.5 g GAC/gC was necessary to obtain an average removal of pharmaceuticals and benzotriazole of 80 % at 20 min contact time, which is comparable to PAC and low granulometry GAC. Higher doses are needed for PFAS but >80 % removals are achievable. Particles, TKN, particulate phosphorus and organic matter are well removed by GAC filtration in both configurations. Biological activity is observed through nitrogen transformation in the GAC bed. Heavy metals are greatly removed in GAC filtration, in particular Cd, Cu, Ni and Pb, probably through biosorption onto the biofilm, developed within the GAC bed. For wastewater reuse applications, GAC filtration has an added value through physicochemical quality improvement and fecal contamination indicators removal of 1 log, facilitating the implementation and optimizing the design of a post-disinfection. Antibiotic resistant bacteria and antibiotic resistance genes are also partially retained in GAC filtration. Finally, biological wastewater treatments combined to GAC filtration is a good solution to effectively treat organic micropollutants together with heavy metals and preparing post-disinfection for reuse.