Effects of disinfectants and particles on the occurrence of different microorganisms in drinking water distribution systems

Abstract

The effects of disinfectants and particles on the occurrence of different bacteria, including total coliforms, heterotrophic plate count (HPC), different opportunistic pathogens (OPs) and amoeba hosts, were investigated in drinking water distribution systems (DWDSs) from five drinking water treatment plants. Total coliforms were not detected in all samples. HPCs were all below 500 CFU mL⁻¹ when the free chlorine residual was higher than 0.05 mg L⁻¹ and the total chlorine residual was higher than 0.35 mg L⁻¹. HPC showed a good relationship with different OPs. Limiting HPC could also control OPs growth in DWDSs. However, Legionella spp., Pseudomonas aeruginosa and Hartmannella vermiformis were 100% positively detected, and Mycobacterium spp. and Legionella pneumophila were more than 90% positively detected in all samples, and pose a health risk to people. Maintaining the free chlorine residual at 0.15–0.20 mg L⁻¹, and the total chlorine residual at 0.35–0.50 mg L⁻¹ can control the OPs growth in DWDSs very well. However, apart from enhancing disinfectant residual concentration, controlling the particle number can also limit OPs growth. This investigation suggests that the particle number should be controlled below 300 in order to control Mycobacterium avium, Legionella pneumophila, and Acanthamoeba spp. growth. The corresponding turbidity should be controlled at 0.25–0.35 NTU. Therefore, there may be a trade-off in the selection of disinfectant residuals or particles to control the OPs growth in DWDSs.