Complexity of Chloramine Decay Kinetics in Premise Plumbing

Area of Science:

• Environmental Science
• Water Treatment Chemistry
• Microbiology

Background:

• Premise plumbing systems are susceptible to opportunistic pathogen growth due to unquantified chloramine decay kinetics.
• Nitrification significantly impacts chloramine stability in water distribution systems.

Purpose of the Study:

• To investigate chloramine decay kinetics in premise plumbing under varying conditions.
• To evaluate the influence of nitrification and temperature on chloramine persistence.
• To compare experimental findings with conventional kinetic models.

Main Methods:

• Conducted experiments using an at-scale premise plumbing rig with mature biofilms and sterile glass jars.
• Tested influent chloramine residuals ranging from <0.2 to 2.5 mg/L.
• Included inoculums with nitrifying bacteria and varied temperatures (19-39 °C).

Main Results:

• Chloramine decay was complete within 8 hours in all tested PEX pipes, with faster decay linked to higher nitrification rates.
• Chloramine persisted better at higher temperatures (37-39 °C) than lower temperatures (19-30 °C), likely due to nitrifier inhibition.
• First-order kinetics accurately modeled chloramine decay in only 8 out of 24 rig experiments; reaction orders varied widely (0.88–2.74).

Conclusions:

• Nitrification and temperature significantly influence chloramine decay in premise plumbing, deviating from standard assumptions.
• Existing kinetic models may not adequately capture chloramine decay behavior in real-world plumbing systems.
• Further research is needed to develop more accurate models for predicting chloramine stability in premise plumbing.