Title page for ETD etd-10262005-123347


Type of Document Master's Thesis
Author Zhang, Yan
Author's Email Address joezhang@vt.edu
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
  • nitrate
  • disinfectant
  • red water
  • iron corrosion
  • sulfate/ chloride ratio
Date of Defense 2005-09-13
Availability unrestricted
Abstract
The 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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