AWWA WQTC60692

Treating drinking water at the treatment plant effluent to meet regulatory requirementsdoes not necessarily ensure high quality water at the consumer's tap. During distribution, waterquality degrades, which may lead to increased bacterial counts with possible coliformoccurrences and depletion of disinfectant residual. The maintenance of a disinfectant residual indistribution systems has traditionally been used to protect microbial water quality. It is necessaryto understand the reasons for the presence and survival of microorganisms in distributionsystems despite the continuing presence of disinfectant residuals. The overall aim of this benchscalestudy was to quantify differences in the inactivation kinetics of E. coli O157:H7 and MS 2phages in the presence of particulate matter, and compare those kinetics to the kinetics obtainedin parallel experiments in pure water.The types of particles that were used in the experiments included iron pipe corrosiondebris (at 50 mg/L), soil contamination to simulate a pipe break (at 50 and 200 mg/L), andmunicipal wastewater solids to simulate cross-contamination (added to reach a water turbidity of2.0 NTU). A soil sample was collected adjacent to a drinking water pipe in Toronto. Corrosion debris were produced by suspending a metal coupon in a flask filled with tap water, andincubating it for a week. Raw wastewater was collected from a Toronto wastewater plant andsterilized by autoclaving. The inactivation kinetics experiments were conducted in 250-mL flasksat 21°C, with agitation to inactivate planktonic microorganisms. The disinfectants tested werefree chlorine and monochloramine. Inactivation was measured as the log₁₀ (N_t / N₀). Ct valueswere calculated by integration of the disinfectant residual concentration (C) up to the givensampling time (t).Statistical comparisons between the slopes of linear regressions of inactivation data forchlorine and monochloramine inactivation in control reactors or in the presence of corrosiondebris, soil, or wastewater were performed to determine if the two data sets were statisticallyequivalent within a 95 percent confidence level (t-test). The results for E. coli O157:H7 showthat the inactivation kinetics with monochloramine in the presence of wastewater debris wassignificantly different from the inactivation kinetics in control reactors, which suggests that thepresence of wastewater debris had a negative (and statistically significant) impact onmonochloramine efficacy. In all other cases with E. coli O157:H7 (including with chlorine),there was no significant difference between inactivation in control water versus inactivation inwater containing debris, suggesting that corrosion debris and soil particles (at the testedconcentrations) did not have an impact on disinfection. Similar results were found with MS 2phages; in other words, the presence of particulate matter had no effect on phage inactivation, regardless ofwhich disinfectant was tested.In conclusion, it appears that particulate matter does not have a significant impact on theinactivation of freely suspended E. coli O157:H7 cells and MS 2 phages, with the exception ofthe effect of wastewater debris on the monochloramine inactivation of E. coli. Particulate matterexerted a demand on the disinfectant residuals (especially chlorine); however, when the resultswere normalized using Ct, the inactivation kinetics of the various treatments were identical. Includes 3 references, tables.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

8

File Size:

1 file , 420 KB