Simple method for quantifying microbiologically assisted chloramine decay in drinking water.

Area of Science:

• Water chemistry
• Environmental microbiology
• Water treatment

Background:

• Monochloramine decay in drinking water is influenced by both chemical and microbiological reactions.
• Accurately distinguishing these decay pathways is crucial for effective water quality modeling and operational control.
• Existing methods lack the ability to separately quantify the contributions of chemical and microbiological decay.

Purpose of the Study:

• To develop a simple method for quantifying the separate contributions of chemical and microbiological reactions to monochloramine decay.
• To define and derive a "microbial decay factor" (Fm) for characterizing microbiologically assisted monochloramine decay.
• To demonstrate the utility of the microbial decay factor in assessing water quality in a distribution system.

Main Methods:

• Comparing monochloramine decay rates in processed (filtered or microbiologically inhibited) and unprocessed water samples.
• Utilizing controlled temperature conditions for sample analysis.
• Defining the microbial decay factor (Fm) as the ratio of microbiologically assisted decay to chemical decay at 20°C.

Main Results:

• The developed method successfully differentiates between chemical and microbiological monochloramine decay.
• The microbial decay factor (Fm) was derived and shown to be a sensitive indicator.
• Analysis of a service reservoir revealed differences in microbiologically assisted decay between bulk and inlet waters, which traditional indicators missed.

Conclusions:

• The microbial decay factor (Fm) provides a novel and sensitive metric for assessing microbiologically assisted monochloramine decay.
• This method offers an early warning system for potential water quality issues related to microbial activity.
• The Fm method enhances the understanding and management of water quality in chloraminated distribution systems.