Characteristics of corrosion sales and biofilm in aged pipe distribution systems with switching water source

Red water has occasionally been observed in the water distribution system of Beijing following a change in the city's water source. Aged cast iron pipes from both affected and unaffected areas were used to establish experimental drinking water distribution systems under different disinfection conditions. The scale deposits formed under different conditions were characterized by X-ray diffraction and scanning electron microscopy, and the bacterial characteristics of the corrosion scales were determined using several molecular methods. The water quality changed less in pipe samples from the unaffected areas than pipes from the affected areas. The pipe samples from the unaffected area included predominantly alpha-FeOOH, Fe3O4, and gamma-FeOOH, and 24.2% nitrate-reducing bacteria (NRB) were predominant with fewer iron-oxidizing bacteria (IOB) being observed. The composition of corrosion products did not exhibit large variation over time although their crystallinity exhibited a slight decrease throughout the duration of the experiment. In contrast, in the pipe samples from the affected, alpha-FeOOH was the main compound with less gamma-FeOOH and Fe3O4, and 3.3% IOB and 12% NRB with few IRB were observed. However, after transporting surface water containing disinfectants, the Fe3O4 and dense corrosion layer formed, inhibiting the release of iron. Moreover, IRB and NRB became dominant. 22.6% and 34.3% NRB appeared in the pipes after chlorination and chloramination, respectively. The synergistic interaction of IRB and NRB with the corrosion layer played a large role in the release of iron from a cast iron pipe following changes in water quality. (C) 2015 Elsevier Ltd. All rights reserved