# Temperature variation for the PSO bulk chlorine decay model in the MSQ module of InfoWorks

The reactive-constituent (PSO) chlorine decay model (Fisher et al. 2017) was provided to users in the MSQ module of InfoWorks in July 2020 (see the MSQ blog for details). A major advantage of this model is that only a single set of four model coefficients is required to characterize decay rate in a given bulk water throughout a distribution system, over a wide range of initial chlorine concentration and any number/size/timing of booster doses, at a single temperature.

Water temperature commonly differs by 20 degrees Celsius between summer and winter, causing reaction (decay) rates to differ typically by a factor of four (or more in warmer climates). Fisher et al. (2012) extended the PSO bulk decay model to account for this temperature variation with the Arrhenius equation, which requires only one additional (fifth) constant coefficient to to complete the characterisation of the same bulk water. The accuracy of the extended model was demonstrated in the same paper and in applications to numerous Australian distribution systems since then.

The five constant coefficients that completely characterise chlorine decay rate must be derived from laboratory decay tests under controlled laboratory conditions because there are many different substances (and concentrations) in a given source water.

I would be pleased to provide Innovyze (or any interested users in the meantime) with the MSQ tables to include the effect of temperature in the MSQ solute data.

The same tables could be used without alteration in Innovyze's InfoWater MSX sofware.

References

Fisher, I; Kastl, G; Sathasivan, A., (2012). A suitable model of combined effects of temperature and initial condition on chlorine bulk decay in water distribution systems. Water Research, 46(10), 3293-3303.

Fisher, I., Kastl, G., Sathasivan, A. (2017). A comprehensive bulk chlorine decay model for simulating residuals in distribution systems. Urban Water Journal, 14(4), 361-368.

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