In-situ sludge ozone-reduction process for effective removal of fluoroquinolone antibiotics in wastewater treatment plants

To date, little is known about the removal of fluoroquinolones (FQs) in the in-situ sludge ozone-reduction (SOR) process. Hence, this study investigated the behavior of five commonly used FQs, including ciprofloxacin, enrofloxacin, lomefloxacin, norfloxacin and ofloxacin in the SOR process. Batch experiments indicated that ozonation could effectively eliminate the target FQs present in the sludge, which was accelerated by increasing the initial pH (5.0-9.5). Continuous operation of an anaerobic/anoxic/oxic process coupled with sludge ozonation and phosphorus recovery showed that the SOR process could achieve zero yield of excess sludge. In addition, chemical oxygen demand and nitrogen species were stably removed, with efficiencies comparable to those obtained in the conventional activated sludge (CAS) process. However, an increase in the effluent total phosphorus concentration was observed in the SOR process. The effluent FQ concentrations in the SOR process remained quite stable and were close to those in the CAS process, whereas the FQ concentrations in the sludge decreased remarkably after ozonation. Mass balance analysis revealed that the FQs were released to the environment mainly through excess sludge disposal (69.9 +/- 2.3%) in the CAS process, whereas were degraded mainly by ozone in the SOR process (75.8 +/- 2.0%). Therefore, the SOR process was able to minimize the excess sludge and the release of FQs to the environment simultaneously.