Iron Release And Water Quality Stability In Drinking Water Distribution Systems

Characteristics of corrosion scales and iron release in drinking water distribution systems are of great concern to water quality protection.In this study,various corrosion scales and pipes were collected from several pipe distribution systems to investigate the interaction between corrosion scales and bulk water.Physico-chemical characteristics of corrosion scales were analyzed using several sophisticated techniques.Bench-scale pipe systems were constructed to investigate the effects of pipe material,water quality and flow velocity on iron release and water quality stability.Jar testing was used to analyze the corrosion of and heavy metal release from galvanized steel.This study aims to provide theoretical basis for water quality protection in drinking water distribution systems.Pipe material,water quality and hydraulic condition significantly influence the formation and characteristics of corrosion scales.Q-style hierarchical cluster analysis and principal component analysis were used to identify elemental accumulation in corrosion scales.Pipe material imposed a significant effect on the accumulation of Fe,Zn and Ca in corrosion scales.Water composition can account for the presence of Si,Al and S in this study.Hydraulic condition was identified as the primary factor influencing the occurrence of O,C and Ca.The multivariate statistical techniques were verified practicable for data interpretation and identification of dominant factors influencing scale characteristics.They can be applied in comparison of outcomes in a wide range of exposure conditions.Under the disturbance such as pipe maintenance or water source switch,water quality stability appeared galvanized iron pipe > unlined cast iron pipe > hybrid pipe.In structural breaks such as elbows or connection joints in pipe systems,diversity of pipe material and complexity of hydrodynamics leaded to the heterogeneity of scale characteristics.These structures tended to release contaminants under changing hydrodynamics and needed stricter protection.Owing to the protection of zinc coating,water qual ity stability in galvanized iron pipe is satisfactory,expect for the high zinc release.However,with the aging of zinc coating,heavy metals such as Pb and Cd would accumulate and be enriched in the corrosion scales,especially at high temperature(36?).These heavy metals tended to release into bulk water during the exposures and posed a great threat to consumers' health.Majority of iron was released in the form of ferric particulates.Iron release,accompanied with consumption of dissolved o xygen and increase of turbidity and color,was the main cause for red water in drinking water distribution systems.The presence of chloride and sulfate facilitated iron release.In contrast,increasing alkalinity alleviated iron release and red water.The increase of dissolved oxygen contributed to maintain the integrity of corrosion scales and thus reduce iron release.