Efficient removal of ciprofloxacin from waste activated sludge by electroactivation of peroxymonosulfate.

Abstract

The waste activated sludge (WAS) generated from sewage treatment accumulates antibiotics including ciprofloxacin (CIP), which may be released into the environments if WAS is not handled properly. Therefore, there is a need to develop technologies aiming at removing CIP from sludge. In this study, electrically activated peroxymonosulfate (E/PMS) was investigated to remove CIP from WAS. The optimal conditions for the degradation of CIP in sludge by E/PMS were determined by response surface methodology (RSM) simulations combined with experimental validation. The highest CIP removal level of 93.8% was achieved in 10 min at a dosage of 250 mg/g dry solid (DS) PMS, and an electrolysis voltage of 23 V. E/PMS facilitated the generation of radicals involved in the elimination of CIP. The contribution of free radicals showed that SO₄ ^•- is more important than HO^• in this process. A degradation pathway for CIP in sludge was proposed based on the detected byproducts and density functional theory (DFT) calculations. The E/PMS process also promoted sludge disintegration, dewatering, heavy metal removal, and morphological transformation. The total content of all six heavy metals decreased, with As and Cr being converted into more stable forms, thereby reducing their leaching rates. The E/PMS process also reduced the toxicity of the sludge filtrate. Finally, the analysis of economic feasibility and energy consumption showed that E/PMS has a significant potential for controlling antibiotics and promoting the harmlessness of sludge. PRACTITIONER POINTS: Effective removal of ciprofloxacin (CIP) from waste activated sludge by electrically activated peroxymonosulfate (E/PMS). Reaction time has little effect on CIP removal from sludge. The degradation sites of CIP in sludge were the piperazine ring, the quinolone fraction, and the cyclopropyl. Promotion of sludge decomposition and dewatering, heavy metal stabilization, and decrease of sludge filtrate toxicity by the E/PMS process.