title: Combination of granular activated carbon adsorption and deep-bed filtration as a single advanced wastewater treatment step for organic micropollutant and phosphorus removal.
abstract: Adsorption onto granular activated carbon (GAC) is an established technology in water and advanced wastewater treatment for the removal of organic substances from the liquid phase. Besides adsorption, the removal of particulate matter by filtration and biodegradation of organic substances in GAC contactors has frequently been reported. The application of GAC as both adsorbent for organic micropollutant (OMP) removal and filter medium for solids retention in tertiary wastewater filtration represents an energy- and space saving option, but has rarely been considered because high dissolved organic carbon (DOC) and suspended solids concentrations in the influent of the GAC adsorber put a significant burden on this integrated treatment step and might result in frequent backwashing and unsatisfactory filtration efficiency. This pilot-scale study investigates the combination of GAC adsorption and deep-bed filtration with coagulation as a single advanced treatment step for simultaneous removal of OMPs and phosphorus from secondary effluent. GAC was assessed as upper filter layer in dual-media downflow filtration and as mono-media upflow filter with regard to filtration performance and OMP removal. Both filtration concepts effectively removed suspended solids and phosphorus, achieving effluent concentrations of 0.1 mg/L TP and 1 mg/L TSS, respectively. Analysis of grain size distribution and head loss within the filter bed showed that considerable head loss occurred in the topmost filter layer in downflow filtration, indicating that most particles do not penetrate deeply into the filter bed. Upflow filtration exhibited substantially lower head loss and effective utilization of the whole filter bed. Well-adsorbing OMPs (e.g. benzotriazole, carbamazepine) were removed by >80% up to throughputs of 8000-10,000 bed volumes (BV), whereas weakly to medium adsorbing OMPs (e.g. primidone, sulfamethoxazole) showed removals <80% at <5,000 BV. In addition, breakthrough behavior was also determined for gabapentin, an anticonvulsant drug recently detected in drinking water resources for which suitable removal technologies are still largely unknown. Gabapentin showed poor adsorptive removal, resulting in rapid concentration increases. Whereas previous studies classified gabapentin as not readily biodegradable, sustained removal was observed after prolonged operation and points at biological elimination of gabapentin within the GAC filter. The application of GAC as filter medium was compared to direct addition of powdered activated carbon (PAC) to deep-bed filtration as a direct process alternative. Both options yielded comparable OMP removals for most compounds at similar carbon usage rates, but GAC achieved considerably higher removals for biodegradable OMPs. Based on the results, the application of GAC in combination with coagulation/filtration represents a promising alternative to powdered activated carbon and ozone for advanced wastewater treatment.
authors: Technische Universität Berlin, Chair of Water Quality Control, Str. des 17. Juni 135, 10623 Berlin, Germany; Berliner Wasserbetriebe, Cicerostr. 24, 10709 Berlin, Germany. Electronic address: johannes.altmann@bwb.de.
authors: Johannes
authors: J
authors: Altmann
authors: Technische Universität Berlin, Chair of Water Quality Control, Str. des 17. Juni 135, 10623 Berlin, Germany.
authors: Daniel
authors: D
authors: Rehfeld
authors: Technische Universität Berlin, Chair of Water Quality Control, Str. des 17. Juni 135, 10623 Berlin, Germany.
authors: Kai
authors: K
authors: Träder
authors: Berliner Wasserbetriebe, Cicerostr. 24, 10709 Berlin, Germany.
authors: Alexander
authors: A
authors: Sperlich
authors: Technische Universität Berlin, Chair of Water Quality Control, Str. des 17. Juni 135, 10623 Berlin, Germany.
authors: Martin
authors: M
authors: Jekel
mesh_terms: D000327:Adsorption; D002606:Charcoal / Q000737:chemistry*; D005374:Filtration / Q000379:methods*; D009930:Organic Chemicals / Q000302:isolation & purification*; D010316:Particle Size; D010758:Phosphorus / Q000302:isolation & purification*; D011208:Powders; D012995:Solubility; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D002606:Charcoal; D009930:Organic Chemicals; D010758:Phosphorus; D011208:Powders; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Adsorption; Deep-bed filtration; Granular activated carbon (GAC); Organic micropollutants; Wastewater treatment