Thermal Methods of Sludge Processing—are They Suitable for Pharmaceuticals and Illicit Drugs Removal from Sewage Sludge?

The presented work aimed to investigate the effect of thermal treatment on sludge from wastewater treatment plants (WWTPs) in the Slovak Republic on the content of pharmaceuticals (PhACs) and illicit drugs. Sludge samples from eight WWTPs (total flows of 6900–62,500 m 3 /day, number of population equivalents over 40,000 for each WWTP, production of sludge 400–3300 tons DM/year) were treated with thermal processes in the temperature range of 80 to 550 °C. More than 100 compounds were studied in the sludge samples, but in this article, we deeply focused on the fate of the thirteen most concentrated and frequently found PhACs (azithromycin, carbamazepine, cetirizine, citalopram and its metabolite N-desmethylcitalopram, diclofenac, fexofenadine, sertraline and its metabolite norsertraline, telmisartan, trazodone, valsartan, and verapamil). The thermal processes used showed a decrease in PhAC concentrations already at 80 °C when the total concentration of selected PhACs decreased to 81%. In thermally treated sludge samples at 250 °C, only telmisartan at all studied WWTPs and diclofenac at WWTP Banská Bystrica stayed above the limits of quantification (LOQs), while the temperature of 550 °C led to a decrease in all thirteen PhACs below LOQs.