Effect of the change in sulphate and dissolved oxygen mass concentration on metal release in old cast iron distribution pipes

To understand the processes of corrosion by-product release and the consequent "red water"problems caused by the variation of water chemical composition in drinking water distribution system,the effect of sulphate and dissolved oxygen(DO) concentration on total iron release in corroded old iron pipe sections historically transporting groundwater was investigated in laboratory using small-scale pipe section reactors.The release behaviors of some low-level metals,such as Mn,As,Cr,Cu,Zn and Ni,in the process of iron release were also monitored.The results showed that the total iron and Mn release increased significantly with the increase of sulphate concentration,and apparent red water occurred when sulphate concentration was above 400 mg.L-1.With the increase of sulfate concentration,the effluent concentrations of As,Cr,Cu,Zn and Ni also increased obviously,however,the effluent concentrations of these metals were lower than the influent concentrations under most circumstances,which indicated that adsorption of these metals by pipe corrosion scales occurred.Increasing DO within a certain range could significantly inhibit the iron release.