Evaluation of the Influence of Drug Complex Formation on the Efficiency of Water Conditioning with Reagents for Tetracycline

The influence of complexation of drug substances using tetracycline as an example on coagulation water treatment was examined. Competition among complexation, coagulation, and precipitation using various reagents was studied. Treatment of wastewaters containing tetracycline with coagulants in an incompletely oxidized state [Fe(II)] was difficult because extremely stable and very soluble complexes formed. The presence of an active pharmaceutical ingredient (tetracycline) in the water being treated led to a pH shift of the precipitation point of hydroxides and in some cases to complete inhibition of the process. It is noteworthy that organic-ligand/iron complexes prevented the precipitation of iron compounds even as sulfides, which theoretically indicated a high stability constant of the iron compounds. It was suggested that the introduction of coagulants based on iron salts into wastewater with a high tetracycline content would increase its concentration and that the related iron-drug complexes could be highly stable, preventing their removal by traditional methods.