Inactivation of particle-associated coliforms by chlorine and monochloramine

Area of Science:

• Environmental Microbiology
• Water Treatment Technologies

Background:

• Wastewater disinfection is crucial for public health.
• Understanding disinfectant efficacy against particle-associated bacteria is essential for effective treatment.

Purpose of the Study:

• To compare the inactivation rates of coliforms by chlorine and monochloramine based on particle size in sewage effluent.
• To investigate the protective effect of particle size on bacterial inactivation.

Main Methods:

• Sewage effluent solids were separated into <7-micron and >7-micron fractions using sieves.
• Indigenous coliforms in each fraction were tested for resistance to chlorine and monochloramine at varying conditions (concentration, temperature, pH).
• Particle counts and inactivation rates (99% inactivation time) were determined.

Main Results:

• Chlorine (0.5 mg/L) inactivated smaller coliforms (<7 microns) faster than larger ones (>7 microns).
• Larger particles (>7 microns) showed a protective effect against chlorine, which was reduced upon homogenization.
• Monochloramine (1 mg/L) showed minimal difference in inactivation based on particle size at pH 7, but inactivated smaller particles faster at pH 8.
• Monochloramine required 20-50 times longer for 99% coliform inactivation compared to chlorine at pH 7.

Conclusions:

• Chlorine is generally more effective than monochloramine for inactivating sewage effluent coliforms.
• Particle size significantly influences chlorine disinfection efficacy, with larger particles offering protection.
• Wastewater treatment strategies should consider particle size when selecting disinfectants and optimizing treatment conditions.