Full-scale anaerobic digestion of sewage sludges: Fate evaluation of pharmaceuticals and main metabolites

Abstract

The occurrence and behavior of pharmaceuticals especially in sewage sludge have attracted great attention nowadays due to the intensive application of sewage sludge in agriculture in terms of the potential adverse effects of pharmaceuticals. Although anaerobic digestion is a well-developed and widely applied treatment process in terms of stabilization of sewage sludges and removal of organics, the treatment performances of this technology for different pharmaceutical subgroups are still not well known. In this study, the occurrence and seasonal variations of 45 pharmaceutical compounds consisting of 27 parent compounds and 18 main metabolites from 10 different therapeutic groups were investigated both in thickened and digested sludge generated in a large-scale urban wastewater treatment plant (WWTP). In this way, the seasonal removal performances of full-scale anaerobic digesters for parent compounds and metabolites have been determined and compared simultaneously. While the total pharmaceutical concentrations in the thickened sludge varied between 21.1 and 177.6 μg/kg seasonally, it was determined in the range of 21.5 and 88.8 μg/kg in the digested sludge. In the thickened sludge, the predominant group was found as antibiotics (35.9 %), while in the digested sludge, it was determined as anticonvulsants (31.3 %). Besides, seasonal relationships of parent compounds and metabolites both in thickened and digested sludges were evaluated statistically in terms of both occurrence and removal. In general, although the capacities for sorption onto sewage sludges were found as different, removal patterns of both parent compounds and metabolites in anaerobic digesters have been determined as quite similar. The removal performance of the anaerobic digesters showed great differences based on the investigated pharmaceutical subgroups. Although varies seasonally, while antibiotic (up to 82.9 %), NSAID (up to 70.9 %), and nerve stimulant (up to 89.6 %) groups tended to be treated in anaerobic digesters, negative removal efficiencies were determined for anticonvulsant (up to −242.9 %), steroid hormone (up to −155.3 %) and antidepressant (up to −5010 %) groups. While the total pharmaceutical treatment performances of anaerobic sludge digesters varied between −78 % (in summer) and 65 % (in winter) seasonally, it has been determined as 28.5 % annually. Therefore, it has been determined in this study that the pharmaceutical treatment performance of full-scale anaerobic digesters is not effective enough.