Type of Document Master's Thesis Author Zhang, Yan Author's Email Address email@example.com URN etd-10262005-123347 Title Relative Effects of Water Chemistry on Aspects of Iron Corrosion Degree Master of Science Department Environmental Engineering Advisory Committee
Advisor Name Title Edwards, Marc A. Committee Chair Dietrich, Andrea M. Committee Member Vikesland, Peter J. Committee Member Keywords
- red water
- iron corrosion
- sulfate/ chloride ratio
Date of Defense 2005-09-13 Availability unrestricted AbstractThe net present replacement value of all publicly and privately owned potable water
pipes in the U.S. is on the order of $2.4 trillion dollars, and costs associated with
deteriorating iron pipes is billions of dollars per year. Problems arising from iron
corrosion include reduced lifetime of the material, scale buildup and energy loss, nonuniform
corrosion and leaks, catastrophic failure, "red water," disinfectant loss and
bacterial re-growth. Iron corrosion is a very complicated process and is affected by many
factors. This research focused on the effect of disinfectant type, sulfate/chloride ratios,
nitrate concentration, and magnesium hardness on iron corrosion. For the waters tested,
chlorine better controlled red water and microbial activity in the bulk solution than
chloramine. Changes in the sulfate/chloride ratio did not have a large effect on iron
corrosion. High levels of nitrate increased the rate of chlorine decay as a result of free
ammonia formation, and also increased the release of iron. Increased magnesium and
zinc decreased the red water caused by high silicate.
Microbiological activity is important in iron corrosion, and control of re-growth in
water distribution systems is a major challenge for water utilities. A separate study
examined the inter-relationship between iron corrosion and bacterial re-growth, with a
special focus on the potential of iron pipe to serve as a source of phosphorus. Under
some circumstances corroding iron and steel may serve as a source for all macronutrients
necessary for bacterial re-growth including fixed carbon, fixed nitrogen and phosphorus.
Conceptual models and experimental data illustrate that levels of phosphorus released
from corroding iron are significant relative to that necessary to sustain high levels of
biofilm bacteria. Consequently, it may be more difficult to limit re-growth on iron
surfaces by limiting phosphorus in the bulk water.
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