Transformation of acetaminophen during water chlorination treatment: kinetics and transformation products identification

As a high-consumption drug in the world, acetaminophen (AAP) has been widely detected in natural waters and wastewaters. Its reactivity and the transformation products formed during chlorination may greatly threaten the safety of drinking water. The reaction kinetics of AAP during chlorination was investigated in this study. The results showed that the reaction kinetics could be well described with a kinetics model of -d[AAP]/dt = k(app)[AAP](t) (0.63)[Cl-2](t) (1.37). The values of apparent rate constant (k(app)) were dependent on reaction temperature, ammonium, and pH. With the increase in reaction temperature from 5.0 +/- 1.0 to 40.0 +/- 1.0 degrees C, the removal efficiency of AAP increased from 60 to 100 %. When ammonium was present in the solution at 2.0 mg/L, the transformation of AAP was inhibited due to the rapid formation of chloramines. The maximum of k(app) was 0.58 x 10(2) M-1.min(-1) at pH 9.0, and the minimum was 0.27 M-1.min(-1) at pH 11.0. A low mineralization of AAP (about 7.2 %) with chlorination was observed through TOC analysis, implying the formation of plenty of transformation products during chlorination. The main transformation products, hydroquinone and two kinds of chlorinated compounds, monochlorinated acetaminophen and dichlorinated acetaminophen, were detected in gas chromatography-mass spectrometry analysis.