Regrowth Evaluation of Coliform Bacteria Injured by Low Chlorine Doses Using Selective and Nonselective Media

Abstract

In this study, the repairing capacity of coliform bacteria injured by chlorine is determined. Chlorine doses from 0.014 to 0.070 mg L⁻¹ were used in according to frequency (up to 38%) of chlorine concentrations detected in a drinking water distribution network, adopted as case study. m-Endo (selective) and m-T7 (nonselective) cultivation media are used. Bacterial regrowth was detected up to 0.035 mg L⁻¹ of chlorine for 4 h of incubation. The coliform bacteria were not able to regrowth when the dose of chlorine increased to 0.07 mg L⁻¹. Bacterial regrowth increased by increasing C:N ratio from 1:40 to 11:40. m-T7 (nonselective) medium allowed to detect bacterial regrowth also for lower incubation periods. Chlorine doses higher than 0.2 mg L⁻¹ dose at water source with a low total organic carbon (TOC) content are recommended to control bacterial regrowth in the distribution network.

Keywords:

• Chlorine
• Coliform bacteria
• Disinfection
• Distribution network
• Injury
• Regrowth
• Selective and nonselective media

Acknowledgment

The authors would like to thank Dr. S. Meriç for her contribution on this article and Dr. Luca Pergamo for his technical assistance.