Structural property and risk assessment of loose deposits in drinking water distribution systems

Abstract

Discoloration events caused by loose deposits resuspension in drinking water distribution systems (DWDS) are the main aspects of customer complaints across the world, but the understanding of the potential risks of loose deposits is insufficient. In this study, loose deposits in real DWDS were collected from regions frequently experiencing ‘yellow water’. Cytotoxicity of healthy human liver cells was used to evaluate the toxicity risks of the particle samples. The results showed that the loose deposits would have a realistic discoloration risk (turbidity > 10 NTU) when their concentrations were higher than 10 mg/L. The water sample containing 1,000 mg/L loose deposits had a dark yellow color (100–300 PCU) and cytotoxicity (viability of human liver cells during cytotoxicity tests 59.18–80.69%), while the water sample containing 1 mg/L loose deposits did not have obvious color (97.00%). Particle size showed a stronger correlation with relative viability (r = 0.761) than other properties (specific area, metal content, contact angle, saturation magnetization and electron transfer number). However, it is interesting to note that both turbidity and color had a low correlation with relative viability, thus the toxicity of the particles could not be properly judged using turbidity or color. This study gives an important guidance that although the loose deposits could be visualized during water discoloration, its toxicity risks could not be evaluated through aesthetic indicators. HIGHLIGHTS Loose deposits >10 mg/L had a realistic discoloration risk.; The cell viability of 1,000 mg/L loose deposit particles was 59.18–80.69%.; Particle size showed a stronger correlation with toxicity than other properties.; Toxicity of loose deposits could not be judged using turbidity or color.;

Keywords

• discoloration events
• drinking water distribution system
• loose deposits