Influence of Metal Speciation in Wastewater Sludge on Antibiotic Distribution

The analytical study was conducted to evaluate the concentration of ciprofloxacin (CIP), chlortetracycline (CTC), and chosen metals in a wastewater treatment plant. The concentration of CIP was slightly higher in the effluent (0.703 ± 0.045 µg/L) than the influent (0.467 ± 0.049 µg/L) in wastewater samples. More than 70% of CTC was recovered during wastewater treatment; its concentration in wastewater effluent was at 6.13 ± 0.863 µg/L. High concentration of CIP and CTC, 3.9 and 11 mg/kg, respectively, were detected in the solid fractions of sludge. This elevated concentration might have been due to interactions with metals in sludge (i.e., 64–89 g/kg of Ca, 52–109 g/kg of Fe) as both antibiotics have the capacity to form complexes with them. The chemical speciation of all sludge types was carried out to further investigate the distribution of targeted metals and antibiotics and to establish if there is any interdependence. The positive correlation between CTC/CIP concentration and Mg, Ca, and As concentration in primary sludge was observed. This suggests that metal-antibiotic interaction may contribute to primary wastewater treatment.