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The growth of total coliforms in these pipes (especially in steel pipe) could be attributed to the decay of chlorine over time as indicated by the significantly reduced residual chlorine concentration. Characklis & Marshall (1990) showed that biofilms can contribute to the loss of disinfectant residuals and increase bacterial levels in a distribution system. This impact of pipe material on biofilm level has been studied by many researchers. Clark et al. (1994) performed experimental study using coupons consisting of various pipe materials representative of those found in distribution. Generally, the ranking of biofilm concentration was polyethylene > PVC > cement. A similar study by Holden et al. (1995) found that the highest level of biofilm was observed in cast iron pipes. However, in this study, new pipes were used and had not been installed in any water distribution system. Thus, the increase of total coliforms might be due to the reaction of chlorine with the pipe material itself. As can be seen, the results from our study indicate that chlorine interacted differently with different pipe material. For example in PVC and steel pipes there was no chlorine residual at all while in the polyethylene pipe residual chlorine was reduced by 50%. Some researchers (Powell et al. 2000) studied chlorine decay in water distribution systems. They reported that pipe material, diameter, initial chlorine concentration, and corrosion are the main factors which control wall chlorine decay. However, since the level of residual chlorine decreased, bacterial regrowth in water distribution systems can occur (Lee 2013). Our results indicated that, in addition to accelerating the chlorine decay, the pipes materials may have also contributed to the growth of bacteria. The highest growth of total coliform (40 CFU/mL) was observed in the steel pipe followed by polyethylene pipe with 10 CFU/mL. In PCV pipe, however, no coliform bacteria was detected despite the absence of chlorine. This could be explained by the fact that microbial growth is related to surface properties of pipes. Norton & Le Chevallier (2000) stated that iron pipes supported more diverse microbial population than PVC pipes. The differences in water quality (growth of coliform bacteria) in different pipes may be due to the release of organic compounds by the pipes material (especially steel and HDPE pipes). Zhang & Liu (2014) investigated organic compounds migration from polymeric pipes into drinking water under long retention times. Their experiment results showed TOC release from all pipes increased significantly over time. However, polyethylene pipes showed the highest TOC concentrations among all tested pipe materials in this study. These results corroborated with those obtained in our study. As can be seen in Tables 6 and 9, the ranking of TOC concentration was polyethylene > steel > PVC.

Table 6

Water quality parameters for samples from different pipe materials in section C for scenario1

Sampling pointChlorine (mg/L)pHTemperature (°C)Turbidity (NTU)TOC (mg/L)
Initial water quality characteristic of sector B 
Initial data 0.37 18.6 1.0 0.40 
Final water quality characteristic of sector B 
PVC pipe 0.0 18.3 1.1 0.80 
HDP pipe 0.1 18.3 1.0 1.75 
Steel pipe 0.0 18.1 1.1 1.01 
Sampling pointChlorine (mg/L)pHTemperature (°C)Turbidity (NTU)TOC (mg/L)
Initial water quality characteristic of sector B 
Initial data 0.37 18.6 1.0 0.40 
Final water quality characteristic of sector B 
PVC pipe 0.0 18.3 1.1 0.80 
HDP pipe 0.1 18.3 1.0 1.75 
Steel pipe 0.0 18.1 1.1 1.01 

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