Inactivation of indicator bacteria in wastewater by chlorine - a kinetics study

The aim of this study was to characterise the kinetics of chlorine consumpt ion and of inactivation of indicator bacteria in secondary wastewater using a batch laboratory reactor. In this time-course study, different concentra tions of chlorine, used as NaOCl, were injected into the reactor, the level s of the different forms of residual chlorine were measured, and the number s of faecal coliforms and faecal streptococci were determined. The results of the kinetics of chlorine consumption showed that monochloramines and tri chloramines were the more important forms of residual chlorine as compared to free chlorine and dichloramines. The high contents of trichloramines ind icated that the reaction of chlorine with ammoniacal nitrogen was very fast and that the transformation of chlorine into trichloramines was carried ou t in a time shorter than I min. Experimental results showed that the applic ation of the model of Chick-Watson in its original form was not representat ive of the kinetics of inactivation of faecal coliforms and faecal streptoc occi. Modification of this model, in considering an initial reduction just at the contact of water with chlorine, improved the results of adjustment o f the model. The same findings are valid for the model of Collins-Selleck i n considering a value m imposed to the concentration of residual chlorine, since it appeared clearly that the concentration of chlorine influenced the output of disinfection more than did the time of contact. (C) 1999 Elsevie r Science Ltd. All rights reserved.