The benefits of powdered activated carbon recirculation for micropollutant removal in advanced wastewater treatment

• Published in: Water research (Oxford) Vol. 91; pp. 97 - 103
• Main Authors: Meinel, F., Zietzschmann, F., Ruhl, A.S., Sperlich, A., Jekel, M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 15.03.2016
• Subjects: Adsorption; Advanced wastewater treatment; Benzotriazole; Charcoal - analysis; Coagulants; Dosage; Effluents; Mathematical models; Multi-stage adsorption; Optimization; Organic Chemicals - chemistry; Organic micropollutants; PAC recirculation; Powdered activated carbon (PAC); Powders; Recycling; Waste Disposal, Fluid - methods; Wastewater treatment; Water Pollutants, Chemical - chemistry; Advanced wastewater treatment; Organic micropollutants; PAC recirculation; Powdered activated carbon (PAC); Multi-stage adsorption
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2016.01.009

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 L−1, removals of benzotriazole and carbamazepine were shown to rise from <40% in the first stage up to >80% in the 11th stage at 30 min adsorption time per stage. At a high PAC dose of 30 mg PAC L−1, 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. [Display omitted] •Batch test for reproducing continuous-flow PAC recirculation process.•Multi-stage loading considerably increases OMP adsorption and loading.•Benefits in OMP removal efficiency are greatest for small PAC doses.•Coagulation does not contribute to OMP removal during multi-stage experiments.•Observed removals can be predicted accurately with the developed model.