Cr release after Cr(III) and Cr(VI) enrichment from different layers of cast iron corrosion scales in drinking water distribution systems: the impact of pH, temperature, sulfate, and chloride

Soft waters characterised with low alkalinity tend to reduce the lifetime of pipes in drinking water distribution systems. Consequently, the corrosion induced is likely to deteriorate water quality at the consumer's tap. Two different types of treatment methods are commonly used to control the corrosion effects of soft waters: (i) the addition of phosphate corrosion inhibitors, and (ii) the remineralisation process. In order to facilitate the decision making of network operator to use suitable treatment methods, a comparative pilot-scale experiment was performed. The above two treatment strategies were tested using pipes representing both drinking water distribution systems (used materials: cast iron and steel) and household plumbing systems (used material: copper). The impact of the two techniques was assessed by means of water quality monitoring (pH, metal leaching, etc) and of corrosion measurements using electrochemical probes as well as weight-loss coupons. The results obtained after a 15 month long experiment showed that remineralisation method was clearly the most effective way to control soft water corrosion. The implementation of this method resulted in a 50% reduction in metals leaching and about 40% decrease in iron corrosion rates.

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Cr(VI) and Cr(III) Release From Different Layers of Cast Iron Corrosion Scales in Drinking Water Distribution Systems: The Impact of pH, Temperature, Sulfate, and Chloride

10.21203/rs.3.rs-273416/v1 ◽

2021 ◽

Author(s):

Yimei Tian ◽

Tiantian Yu ◽

Jingyi Shen ◽

Guolei Zheng ◽

Han Li ◽

...

Keyword(s):

Drinking Water ◽

Distribution Systems ◽

Water Distribution ◽

Water Distribution Systems ◽

Extraction Procedure ◽

Surrounding Water ◽

Drinking Water Distribution Systems ◽

Drinking Water Distribution ◽

Corrosion Scales ◽

The Impact

Abstract Chromium accumulated from source water and pipeline lining materials in corrosion scales could potentially be released into bulk water in drinking water distribution systems (DWDS). Chromium behaviors between corrosion scale phase and the surrounding water phase vary spatially in different layers and temporally in different DWDS running periods. In this study, corrosion scales sampled from actual DWDS were first characterized by SEM, XRD, XRF, and the modified BCR three-step sequential extraction procedure. Then scales were divided into the outer and inner layers for subsequent analysis. Static accumulation and release experiments were performed with Cr(VI) and Cr(III) on two distinct scale layers to systematically assess the influence of pH, temperature, sulfate, and chloride. The release behaviors of Cr(VI) under the co-effect of multiple factors were investigated in orthogonal experiments. Results showed that in the outer and inner layers of corrosion scales, chromium exhibited differences in accumulation and release behaviors, with the outer layer accumulating less and releasing more. The mechanisms of chromium retention based on different iron (oxyhydr)oxides were discussed.

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