PAC adsorption is a widespread option for the removal of organic micropollutants (OMP) from secondary
effluent. For an optimal exploitation of the adsorption capacity, PAC recirculation is nowadays a common
practice, although the mechanistic interrelations of the complex recirculation process are not fully
resolved. In this work, extensive multi-stage batch adsorption testing with repeated PAC and coagulant
dosage was performed to evaluate the continuous-flow recirculation system. Partly loaded PAC showed a
distinct amount of remaining capacity, as OMP and DOC removals considerably increased with each
additional adsorption stage. At a low PAC dose of 10 mg PAC L1, removals of benzotriazole and carbamazepine
were shown to rise from 80% in the 11th stage at 30 min
adsorption time per stage. At a high PAC dose of 30 mg PAC L1, OMP and DOC removals were significantly
higher and reached 98% (for benzotriazole and carbamazepine) after 11 stages. Coagulant dosage
showed no influence on OMP removal, whereas a major part of DOC removal can be attributed to
coagulation. Multi-stage adsorption is particularly beneficial for small PAC doses and significant PAC
savings are feasible. A new model approach for predicting multi-stage OMP adsorption on the basis of a
single-stage adsorption experiment was developed. It proved to predict OMP removals and PAC loadings
accurately and thus contributes towards understanding the PAC recirculation process.