DISINFECTION KINETICS OF HETEROTROPHIC PLATE-COUNT BACTERIA IN BIOLOGICALLY TREATED POTABLE WATER

The disinfection kinetics of biologically and non-biologically treated drinking waters were evaluated at bench-scale using process water fro m a pilot plant employing pre-ozonation and biologically active carbon (BAC) contactors. The Chick-Watson kinetic model did not describe the inactivation of native heterotrophic plate count bacteria (R2A agar, 7d at 20 degrees C) with decreasing rates of inactivation seen at exte nded contact times in all process streams. The parameters were estimat ed for the Hom kinetic model using a non-linear least squares method. The estimates of k, n, and m parameters for the Hom model using the ki netic data from the biologically and non-biologically treated waters w ere found to be statistically different between the two waters for bot h free chlorine and preformed monochloramine. However, if sufficient c ontact time was provided, the overall inactivation was the same in the control and biologically-treated streams. The observed kinetic differ ences were thought to be due to a highly resistant subgroup within the heterotrophic plate count bacteria population in each water.