Chromium immobilization and release by pipe scales in drinking water distribution systems: The impact of anions

Due to its high toxicity, the release of chromium (Cr) by pipe scales poses a serious risk to drinking water quality and human health. This study looked into how Cr immobilized and released by pipe scales. SEM, XRD, and XPS were applied to evaluate the physicochemical characterization of pipe scales. To identify times of immobilization and release and the proper scale to water ratio, the behaviors of Cr were examined in stagnation experiments. Afterward, the common anions in drinking water were designed as nine concentration gradients to explore their species and concentrations impacts on the immobilization and release process of Cr. It is worth mentioning that the pipe scales were classified into block pipe scales, lumpy pipe scales, and powder pipe scales in this experiment. The types of pipe scales were rarely considered as an influencing factor. Results revealed that in contrast to powder pipe scales, block pipe scales and lumpy pipe scales exhibited extremely comparable trends. Specifically, in terms of accumulation capacity, the order from largest to smallest was powder pipe scales, lumpy pipe scales, and block pipe scales. However, the potential of Cr release from block pipe scales was the highest, indicating a high danger of heavy metal re-release in actual circumstances. Findings from this study discovered the turning points of chloride and sulfate concentrations associated with the pipe scales species in the anion-promoted release. These results provide insight into the relationship between pipe scales and Cr in drinking water distribution systems (DWDS).