ABSTRACT
<p><b>OBJECTIVE</b>To introduce a new sequential chlorination disinfection process in which short-term free chlorine and chloramine are sequentially added.</p><p><b>METHODS</b>Pilot tests of this sequential chlorination were carried out in a drinking water plant.</p><p><b>RESULTS</b>The sequential chlorination disinfection process had the same or better efficiency on microbe (including virus) inactivation compared with the free chlorine disinfection process. There seemed to be some synergetic disinfection effect between free chlorine and monochloramine because they attacked different targets. The sequential chlorination disinfection process resulted in 35.7%-77.0% TTHM formation and 36.6%-54.8% THAA5 formation less than the free chlorination process. The poorer the water quality was, the more advantage the sequential chlorination disinfection had over the free chlorination.</p><p><b>CONCLUSION</b>This process takes advantages of free chlorine's quick inactivation of microorganisms and chloramine's low disinfection by-product (DBP) yield and long-term residual effect, allowing simultaneous control of microbes and DBPs in an effective and economic way.</p>