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Effect of sulfate on the transformation of corrosion scale composition and bacterial community in cast iron water distribution pipes
Citation:
Yang, F., B. Shi, Y. Bai, H. Sun, D. Lytle, AND D. Wang. Effect of sulfate on the transformation of corrosion scale composition and bacterial community in cast iron water distribution pipes. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 59:46-57, (2014).
Impact/Purpose:
To inform the public.
Description:
The stability of iron corrosion products and the bacterial composition of biofilm in drinking water distribution systems (DWDS) could have great impact on the water safety at the consumer ends. In this work, pipe loops were setup to investigate the transformation characteristics of iron corrosion products and bacterial community on old cast iron distribution pipes under feed water quality changing scenarios. The principal feed waters were treated groundwater, surface water and simulated water with elevated sulfate concentration. For the loops established with pipes historically transporting surface water, switching to simulated water with higher sulfate did not trigger severe iron release; only long-time stagnation and decreased disinfectant concentration transitorily deteriorated water quality. For the loops established with pipes historically transporting groundwater or blends, surface water and simulated water with elevated sulfate concentration triggered higher iron release. For the pipes historically transporting groundwater or blends, the corrosion scales had increased Fe3O4 content, decreased FeCO3, green rust (Fe6(OH)12CO3) and β-FeOOH contents when switched to waters with elevated sulfate concentrations. Whereas, for the pipes historically transporting surface water, the corrosion scale constituents changed to a much less extent with relatively higher proportion of Fe3O4 all through the experiment. Pyrosequencing of 16S rRNA analysis for biofilm indicated that scales on pipes historically transporting surface water always hold the dominant bacterial group - iron reducing bacteria (IRB) under water quality changing period, while scales on pipes historically transporting groundwater or blends had much lower fraction of IRB. When switching to higher sulfate water, biofilm on pipes historically transporting groundwater or blends had increased abundance of sulfur oxidizing bacteria (SOB), sulfate reducing bacteria (SRB) and iron oxidizing bacteria (IOB), which had synergistic effect on corrosion processes and corrosion by-products formation. Although pipes historically transporting groundwater or blends had higher iron release under water quality changing period, their corrosion scales tended to form more stable constituents and their iron release were gradually stabilizing with time.
