Chlorination and chloramination of tetracycline antibiotics: Disinfection by-products formation and influential factors

Formation of disinfection by-products (DBPs) from chlorination and chloramination of tetracycline antibiotics (TCs) was comprehensively investigated. It was demonstrated that a connection existed between the transformation of TCs and the formation of chloroform (CHCl 3 ), carbon tetrachloride (CCl 4 ), dichloroacetonitrile (DCAN) and dichloroacetone (DCAce). Factors evaluated included chlorine (Cl 2 ) and chloramine(NH 2 Cl) dosage, reaction time, solution pH and disinfection modes. Increased Cl 2 /NH 2 Cl dosage and reaction time improved the formation of CHCl 3 and DCAce. Formation of DCAN followed an increasing and then decreasing pattern with increasing Cl 2 dosage and prolonged reaction time. pH affected DBPs formation differently, with CHCl 3 and DCAN decreasing in chlorination, and having maximum concentrations at pH 7 in chloramination. The total concentrations of DBPs obeyed the following order: chlorination>chloramination>pre-chlorination (0.5   h)>pre-chlorination (1   h)>pre-chlorination (2   h).