| Metal pipe corrosions are typically important accumulation places for Heavy metals in drinking water distribution system, and the accumulated heavy metals may be released suddenly when the water quality conditions changes, causing serious drinking water safety problems. Based on a survey on the contents of typical heavy metals existing in part of the cities in China, the accumulation and release performances of heavy metals on the pipe corrosion materials under different water quality conditions were investigated in this paper. The main results obtained in this study were listed as following:(1) It was determined that the concentrations of arsenic, chromium, nickel, copper, zinc, cadmium, selenium, and mercury in all the collected water samples were lower than the maximum permission value; The concentrations of iron, manganese, and lead in some water samples could not meet the standard requirement. The maximum concentration of iron reached 704.0 ?g/L, approximately 2.35 times as high as the maximum permission value. Meanwhile, all the contentrations of arsenic, chromium, nickel, lead, iron, copper, zinc, cadmium, selenium, and mercury were lower when the water stayed for longer time in above 60% networks, indicating that a long retention time would promote the transfer of heavy metals from drinking water to the metal pipe corrosion.(2) The corrosion materials formed in water supply networks showed a notable adsorption capacity for zinc, copper, manganese, chromium, lead, mercury, nickel, arsenic, cadmium, and selenium. The adsorption process follows the pseudo-second order reaction kinetics. The adsorption of lead and mercury was the fastest, and more than 99% of them could be adsorbed within 5 min under the experimental water temperature and pH conditions. Different from other elements, the adsorption of chromium on the pipe corrosion materials decreased gradually with time, and less chromium was removal from the water solution. Meanwhile, the removal rate of chromium also decreased gradually as the increase of its initial concentration in adsorption. When the initial concentration of chromium was 50 ?g/L, the adsorption rate was the highest, approximately 66.72%. increasing the initial concentration of chromium to 500 ? g/L, its adsorption rate decreased to 40.79%. The effects of solution pH on the accumulation process of heavy metals mainly depended on the solubility of heavy metals and its combination capacity with pipe corrosions.(3) The stability of the heavy metals adsorbed in the pipe corrosion materials was highly affected by the environmental conditions. It was determined that the variation of water temperature would not cause the release of both copper and lead from the pipe corrosion materials; while the released amount of other heavy metals would increase gradually as the increase of water temperature. Meanwhile, all the heavy metals showed a similar releasing law as the variation of solution pH. At pH 7.0, the amount of heavy metals released from the pipe corrosions was could be ignored. Decreasing or increasing the solution pH, however, would both cause a suddenly release of the selected heavy metals. Similar to solution pH, except copper, mercury, and lead, the increase of alkalinity would also cause the release of heavy metals. Besides, except selenium and chromium, the variation of hardness would not cause the release of heavy metals.The pipe corrosion existing in water supply networks showed a strong adsorption ability for heavy metals, and extending the hydraulic retention time would be benefit to the adsorption of heavy metal. However, the variation of water quality in the pipeline, such as an increase in solution, alkalinity, and hardness, would cause some of heavy metals releasing from the pipe corrosion material suddenly, which would help to maintain a stable heavy metal element content in the drinking water supply networks. |
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