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∼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.

无衬里铁管（UIP）在饮用水配水系统（DWDS）中仍然广泛使用，由于铁的释放，长时间保留后容易变色，但在这种情况下初始氯对水质的影响尚不清楚。在这里，我们研究了 UIP 段反应器在不同初始氯剂量下的水质变化。结果表明，UIP 中氯气在 0.5 h 内迅速消失。初始氯含量较高（5 mg/L）的水在短时间内（1.5 h内）浊度较高，但在较长的停留时间（2～12 h）内，浊度最高的是无初始氯的铁管。有趣的是，随着初始氯的增加，观察到 UIPs 中三磷酸腺苷的明显增加，这与异养菌落计数的结果一致。多糖和蛋白质随着初始氯的增加而增加，有利于形成抑制腐蚀的保护层。该研究表明，在 UIP 中过夜保留期间，提高氯含量可有效控制变色，但可能会增加化学和微生物风险。