Effects of chloramine (NH2Cl) and its combination with chlorine dioxide(NH2Cl/ClO2)on dissolved organic matter (DOM) were studied by annular reactor. The characteristic of DOM was evaluated by monitoring removal efficiencies of dissolved organic carbon (DOC) and UV254

overall DOM concentration

specific DOM absorbance ratio and excitation-emission matrices spectra (EEMs). The results showed that the oxidants significantly affected the removal of overall DOM

DOC and UV254. The DOM removal efficiency was lower after NH2Cl/ClO2 compared with that of NH2Cl

however

the recovery efficiencies speed of them were similar in the two cases. The degradation of DOM

DOC and UV254 recovered on 5th day

4th day and 1st day after oxidation

respectively. Aromatic rings were substituted predominantly with polar groups after oxidation

and thus the oxidant increased the biodegradable DOM. Overall

DOM fluorescence intensity had a decrease potential after oxidant

particularly for tryptophan-like fluorescence and humic-like fluorescence. The aromatic rings were easier targeted by NH2Cl/ClO2

however

much more functional groups such as hydroxyl

carboxyl and carbonyl

and higher biodegradable DOM were observed after NH2Cl

resulting in higher biodegradation of DOM. The DOC and UV254 degradation after NH2Cl or NH2Cl/ClO2 could both recover to a higher level than that in control. Therefore

compared to single NH2Cl

NH2Cl/ClO2 was proposed to use in the raw water distribution system for decreasing oxidant by-products.