Effects of chloride and humic acid on iron release in water distribution system

Abstract

In order to acquire better understanding of steel pipe scale constructions and how water quality factors influence iron release process,pipe scale samples of 10 to 15 year-old pipes were collected and analyzed with SEM,EDS and XRD.Using indoor pipe reactor simulating stagnation environment,experiments were conducted to study effects of chloride,humic acid and dissolved oxygen on iron release process under different concentrations.Results indicate that pipe scale surface is covered with shell-like layer and filled with loose and porous course inside.Major elements are Fe,O and C,and main substances are Fe3O4,FeOOH and FeCO3.Concentrations of chloride and humic acid both have significant positive correlation with iron release quantity.Iron release caused by chloride is mainly precipitant state with a proportion more than 85.02%,and water turbidity acts the same with iron concentration with maximum value of 45.5.Under conditions with humic acid,the proportion of precipitant iron decreases dramatically with an average value of 20.41% and maximum value of 39.39%.Thus water turbidity change is not significant.Under low initial dissolved oxygen condition,total iron and dissolved iron concentration increases 54.9% and 67.7% compared to normal condition.