Solid–Liquid Distribution of Ciprofloxacin during Sludge Dewatering after Fe(II)-Activated Peroxymonosulfate Treatment: Focusing on the Role of Dissolved Organic Components

Abstract

The role of dissolved organic components in the solid–liquid distribution of ciprofloxacin (CIP) during sludge dewatering by Fe­(II)-activated peroxymonosulfate treatment was investigated in both anaerobic digested sludge (ADS) and waste activated sludge (WAS). After treatment, CIP (15% for ADS and 27% for WAS) was partially degraded within the solid sludge phase, but a majority of CIP was still present in the solid sludge phase. The entire process led to an increase of CIP concentration within the liquid phase of both ADS and WAS, along with the increase of dissolved organic components in the liquid sludge phase. Fractionation of dissolved organic components by size exclusion chromatography coupled with online organic carbon detection showed that CIP concentration in the liquid phase was positively correlated with the high molecular fraction existed therein (assigned to biopolymers; regression coefficient = 0.99, probability <0.05). Further studies with model dissolved organic components showed that the dissolved organic components influenced the CIP presence in the liquid phase through (1) inhibiting the adsorption of CIP onto sludge flocs, as indicated by the decreased adsorption capacity at equilibrium for both ADS and WAS and (2) retarding CIP degradation in the liquid phase by Fe­(II)-activated peroxymonosulfate treatment.