# Complexity of Chloramine Decay Kinetics in Premise Plumbing

## TL;DR

This study explores how chloramine decays in household plumbing systems, revealing that decay rates are influenced by factors like temperature and nitrifying bacteria.

## Contribution

The study provides new insights into chloramine decay in premise plumbing, challenging conventional kinetic assumptions and modeling approaches.

## Key findings

- Chloramine decay was complete after 8 hours in all PEX pipes tested.
- Higher temperatures improved chloramine persistence due to nitrifier inhibition.
- Chloramine decay reaction order varied widely among pipes, from 0.88 to 2.74.

## Abstract

Nitrification-driven chloramine decay kinetics have largely
been
unquantified in premise plumbing, which is particularly vulnerable
to opportunistic pathogen growth. Here, we carried out complementary
experiments in an at-scale premise plumbing rig with mature biofilms
(>4 years age) with influent residuals of <0.2, 0.25, 0.5, 1.0,
and 2.5 mg/L as Cl2 and sterile glass jars, with and without
an inoculum containing nitrifying bacteria. Chloramine decay was complete
after 8 h of stagnation in all PEX rig pipes (n = 16), tested over
a range of diameters (1/4–3/4”) and flow rates (0.25–2.2
gpm), with decay rates increasing in situations with higher nitrification
rates. The jar experiments revealed that chloramine actually persisted
better at higher (37–39 °C) than lower (19–30 °C)
temperatures, contrary to standard temperature-adjusted kinetic assumptions,
presumably because nitrifiers are inhibited at higher temperatures.
Contrary to assumptions made in conventional models, chloramine decay
was only effectively modeled as first order in 8/24 cases in the rig
experiment (R2 > 0.9). The best fit chloramine decay
reaction
order varied among the rig pipes from 0.88 to 2.74, depending on chloramine
dose and exposure time, hydraulics, and modeling method.