Development of disinfection-resistant bacteria during wastewater treatment

The Walliamsburg, Virginia, wastewater treatment plant (WWTP) has periodica lly experienced erratic disinfection and persistence of fecal coliform bact eria in the presence of apparently adequate levels of disinfectant in the e ffluent. Several reasons for disinfection problems were previously investig ated. This paper describes the results of a study of two factors that could affect disinfection in this plant: (1) the potential for the development o f disinfection-resistant fecal coliforms in the operation of this specific WWTP and (2) the nature of the wastewater matrix that this particular WWTP handles that could interfere with chlorine disinfection. The study suggeste d that the WWTP oxidation lowers supported growth or recovery of fecal coli form bacteria. This bacterial subpopulation seemed to have increased resist ance to routine chlorine disinfection. Inactivation rate constants calculat ed for periods between 15 and 45 minutes after chlorine addition were signi ficantly lower for fecal coliforms originating from oxidation towers than f or fecal coliforms from other sources. This is, to our knowledge, the first report of such conditions created by a treatment process. The study of the plant-specific matrix determined no statistically significant effects on d isinfection.