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 from 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, 7 d at 20°C) with decreasing rates of inactivation seen at extended contact times in all process streams. The parameters were estimated 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 kinetic data from the biologically and non-biologically treated waters were found to be statistically different between the two waters for both free chlorine and preformed monochloramine. However, if sufficient contact time was provided, the overall inactivation was the same in the control and biologically-treated streams. The observed kinetic differences were thought to be due to a highly resistant subgroup within the heterotrophic plate count bacteria population in each water.