Examination and characterization of distribution system biofilms

Area of Science:

• Environmental microbiology
• Water quality management
• Public health

Background:

• Drinking water utilities can face persistent bacteriological issues in distribution systems.
• Treatment plant effluents may be free of coliform bacteria, yet distribution systems show contamination.
• Biofilms in distribution systems are implicated in water quality degradation.

Purpose of the Study:

• To investigate the role of distribution system biofilms in water quality problems.
• To identify the sources and characteristics of coliform bacteria in the distribution system.
• To evaluate the effectiveness of current control measures against coliforms in biofilms.

Main Methods:

• Monitoring coliform levels throughout the distribution system.
• Identifying coliform species and their distribution.
• Analyzing biofilm composition, including heterotrophic plate count bacteria and coliforms.
• Measuring assimilable organic carbon (AOC) levels.
• Assessing the efficacy of chlorine residual and physical cleaning methods.

Main Results:

• Coliform levels increased with distance from the treatment plant.
• High coliform densities were primarily found in iron tubercles within biofilms.
• Coliform bacteria in biofilms matched those found in the water column.
• Assimilable organic carbon levels decreased along the distribution system.
• A 1.0-mg/liter free chlorine residual and physical cleaning were insufficient to control coliforms.

Conclusions:

• Distribution system biofilms, especially in iron tubercles, are a significant reservoir for coliform bacteria.
• Coliform growth in biofilms can mask true treatment failures and compromise water safety.
• Further research is needed to develop effective methods for controlling coliform bacteria in pipeline biofilms.
• Current disinfection and cleaning strategies are inadequate for managing biofilm-related coliform contamination.