Interaction of ciprofloxacin with the activated sludge of the sewage treatment plant.

Interaction of ciprofloxacin with the activated sludge of the sewage treatment plant is of importance for the ciprofloxacin migration and risk control. More than 96.0% ciprofloxacin was removed through the sludge adsorption. The sludge surface charge varied little with ciprofloxacin since most ciprofloxacin was dissociated into the neutral one. No obvious shift was observed for the soluble carbohydrate concentration and composition with the addition of ciprofloxacin, indicating the weak interaction between the carbohydrates and ciprofloxacin. The introduction of ciprofloxacin resulted in a reduction of the soluble protein concentration, a marked increase of the extracellular protein fluorescence intensities, and a dramatic emergence of new extracellular proteins. The alteration of the proteins highlights the strong interaction between the extracellular proteins and ciprofloxacin, and the consequent integration of certain soluble proteins and original unextractable inner layer extracellular proteins into the extractable extracellular proteins. Different types of interactions are suggested to dominate between the extracellular proteins and the differently dissociated ciprofloxacin.