To obtain a safe and stable drinking water, more attention has been recently given to understanding water quality changes that take place within the water distribution networks(WDN) as well as protection of water supply sources and upgrading of the existing water treatment plant. Main causes of water quality deterioration in WDN are as follows: microbial contamination caused by breakthrough, regrowth, and aftergrowth; infiltration of pollutants through the cross connection; release of corrosion by-product and coating material; and formation of disinfection by-product(DBP). To obtain a safe and stable drinking water, more attention has to be focused on understanding phenomena that take place within the water distribution network(WDN) in addition to raw water reservation, upgrading of the existing water treatment plant.
To control the microbial contamination and the DBP formation and monitor the water quality changes in WDN, distribution of chlorine residuals in the networks is often checked. Recently a number of computer models have been developed to calculate the distribution and in turn to estimate the water quality changes in WDN. Especially, the spatial and temporal chlorine residual concentrations in WDN can be easily estimated by the models. It is noted, however that these models are not able to reflect effects of the spatial variations of such parameters as pipe material, construction age, and pipe wall condition on the distribution of chlorine residuals.
This research attempted to estimate the changes of chlorine residual in WDN including the effects from such parameters and their spatial variations. In the simulated distribution networks(SDN) with different pipe materials, chlorine decay coefficients are estimated and compared to see the effects of pipe materials on the chlorine residual decays. When the cement-lined cast iron(CLCI) and PVC are used for SDN, respectively, the chlorine decay coefficient in the CLCI network is about 3 times as high as that of the PVC one. In addition, the decay pattern in the CLCI network is very rapid during the initial circulation and then becomes slow. This indicates that different chlorine decay coefficients are required for different pipe materials in WDN to predict the correct distribution of chlorine residuals.
In the batch experiment, an equation to predict the concentration of chlorine residual in relation with various water quality parameters and temperature is developed using the multi-regression analysis. Five parameters are selected based on their impact on chlorine residual decay and include TOC, Fe, initial Chlorine concentration, contact time, temperature. TOC and temperature have proved to positively affect on the decay. However, iron concentration(Fe) is found to negatively affect and thus delays the decay.
