Impact of initial chlorine concentration on water quality change in old unlined iron pipes

Unlined iron pipe (UIP) is still widely in use in drinking water distribution systems (DWDS), discoloration easily happens after a long-time retention due to iron release, but the influence of initial chlorine on water quality under this condition is not clear. Here, we studied the water quality changes in UIP section reactors under different initial chlorine dosages. Results showed that chlorine could disappeared rapidly within 0.5 h in the UIP. The water with higher initial chlorine (5 mg/L) had higher turbidity in a short time (within 1.5 h), but for a longer retention time (2 similar to 12 h), the highest turbidity was in the iron pipe without initial chlorine. Interestingly, a clear increase in adenosine triphosphate in the UIPs was observed with the increase of initial chlorine, which was in accordance with the results of heterotrophic plate count. Polysaccharide and protein increased with the increase of initial chlorine, which would benefit the formation of a protective layer to inhibit corrosion. This study reflects that during the overnight retention in UIP, raising chlorine would be effective to control discoloration, but chemical and microbiological risks may increase.

Automated summary

This study investigated the water quality changes in UIP section reactors under different initial chlorine dosages. The results showed that chlorine disappeared rapidly in the UIP. Water with higher initial chlorine had higher turbidity in a short time, but for a longer retention time, the highest turbidity was observed in the iron pipe without initial chlorine. Furthermore, an increase in adenosine triphosphate and heterotrophic plate count was observed with the increase of initial chlorine. Polysaccharide and protein levels also increased with the increase of initial chlorine, promoting the formation of a protective layer to inhibit corrosion.