Research Of Influencing Factors On Iron Release In Water Distribution System

Due to the increasing requirement of water quality safety, the iron stability problem has been a major concern in drinking water industry recently. The topic of maintaining iron stability and controlling iron releasing problem has become an important task. In order to explore the reason for iron release phenomenon occurs and the factors causing excessive iron concentration in bulk water, experiments are conducted using bench-scale pipe reactor to simulate stagnation environment and pilot-scale distribution system to simulate hydraulic conditions. This project aims to help acquire better understanding and provide some theoretical proof of iron release pattern in water through systematic experiments on factors that would affect iron stability and their change influence.Corrosion takes place in iron pipes and pipe scale layer is the main material source of excessive iron in bulk water, the bulk water quality can affect pipe scale layer structure and composition. Pipe scale samples collected from10to15year-old pipes were analyzed with SEM, EDS and XRD to study their physical structural characteristics and chemical composition.It is good practice to conduct experiments with real corrode steel pipe acquired from southern China. In-door pipe reactor devices are built to regulate water quality factors such as chloride, sulfate, dissolved oxygen, residual chlorine and so on, were investigated to study their influences on iron release and related mechanisms. Results indicate that both concentrations of major anions and organic matters show significant positive correlation with iron release quantity. Iron release caused by anions is mainly precipitant state and water turbidity acts the same with iron concentration. However, in the presence of organic matters, the proportion of precipitant iron decreases dramatically while total iron release quantity is high. Thus water turbidity change is not significant in some circumstances. Dissolved oxygen declines and water quality deteriorate along with the stagnation time. Under low initial dissolved oxygen condition, total iron and dissolved iron concentrations increase. Residual chlorine has similar effects with dissolved oxygen. By using pilot-scale distribution system simulate hydraulic conditions, different velocities, temperatures, stagnation periods are experimented. It is inferred that temperature and stagnation time have positive influence on iron release. Normally, increase velocity would help reduce iron release. However, high velocity may cause higher iron concentrations due to flush and scouring action.