Affiliations: Department of Environment Science and Technology,
Tsinghua University, Beijing 100084, China | Tianjin Water Works Limited Company, Tianjin 300000,
China
Abstract: A field study on the estimation and analysis of iron stability in
drinking water distribution system was carried out in a city of China. The
stability of iron ion was estimated by pC-pH figure. It was found that iron ion
was unstable, with a high Fe (OH)_3 precipitation tendency
and obvious increase in turbidity. The outer layer of the corrosion scale was
compact, while the inner core was porous. The main composition of the scale was
iron, and the possible compound constitutes of the outer scale were
α-FeOOH, γ-FeOOH,
α-Fe_2O_3,
γ-Fe_2O_3,
FeCl_3, while the inner were
Fe_3O_4, FeCl_2,
FeCO_3. According to the characteristics of the corrosion
scale, it was thought that the main reason for iron instability was iron
release from corrosion scale. Many factors such as pipe materials, dissolved
oxygen and chlorine residual affect iron release. Generally, higher iron
release occurred with lower dissolved oxygen or chlorine residual
concentration, while lower iron release occurred with higher dissolved oxygen
or chlorine residual concentration.The reason was considered that the
passivated out layer of scale of ferric oxide was broken down by reductive
reaction in a condition of low oxidants concentration, which would result more
rapid corrosion of the pipe and red water phenomenon.
Keywords: chlorine residual, corrosion scale, dissolved oxygen, drinking water distribution systems, iron release, iron stability
