Reducing free residual chlorine using four simple physical methods in drinking water: effect of different parameters, monitoring microbial regrowth of culturable heterotrophic bacteria, and kinetic and thermodynamic studies

Abstract

While chlorination is critical for water disinfection, a knowledge gap includes the nature of free residual chlorine (FRC) decay, which was investigated using four physical methods (SSA, SSR with and without a lid, heating, and incubator shaker). Keeping water samples in SSA and SSR methods for 24 h resulted in the FRC decline by 62% and 51%, respectively. The heterotrophic plate count (HPC) increased significantly between initial (3.17 ± 2.6–3.82 ± 1.1 CFU/mL) and final samples (6.7 ± 1.5–94.7 ± 4.72 CFU/mL) for both SSA and SSR methods. Thermodynamic behavior (ΔH versus ΔG) of FRC decay of the different methods was characterized.

Keywords:

• Drinking water
• free residual chlorine
• thermokinetics
• HPC
• chlorination

Acknowledgement

This study was supported by Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences.

Disclosure statement

The authors declare that they have no conflict of interest.

Additional information

Funding

This study was supported by the Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences.