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Permanent link (DOI): https://doi.org/10.7939/R3CC0V571

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Corrosion of Aluminum Alloys in Wastewater Treatment Aeration Tanks Open Access

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Other title
Subject/Keyword
Stainless Steel
Wastewater
Depassivation
Corrosion
Aluminum
Passivation
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Pavelich, John Scott
Supervisor and department
Nychka, John (Chemical and Materials Engineering)
Examining committee member and department
Kresta, Suzanne (Chemical and Materials Engineering)
Etsell, Thomas (Chemical and Materials Engineering)
Nychka, John (Chemical and Materials Engineering)
Department
Department of Chemical and Materials Engineering
Specialization
Materials Engineering
Date accepted
2017-03-22T14:48:46Z
Graduation date
2017-06:Spring 2017
Degree
Master of Science
Degree level
Master's
Abstract
Severe localized corrosion was found throughout an aeration tank of a modular wastewater treatment plant. Specifically, pitting, crevice corrosion, galvanic corrosion, and intergranular corrosion (IGC) were observed on the 5000 and 6000 series aluminum alloys used in the tank’s construction. One of the suspected environmental causes of corrosion was an aeration tank process additive, namely a coagulant – either aluminum sulphate (Alum) or polyaluminum chloride (PACl; Isopac). Laboratory scale corrosion cells were designed to isolate, simulate, and evaluate the corrosivity of the coagulants (in relevant quantities) on the metallic alloys of construction. Additionally, due to presence of deposit found throughout the tank (resulting in under-deposit corrosion), fabricated crevices were installed on the tested alloys to help simulate crevice corrosion environments. The solution conditions in the cells were monitored throughout the duration of the immersion testing in order to assess whether the cells were within normal operating conditions of the corroded aeration tank. A series of material characterizations and mass change measurements were performed on the corrosion coupons post-testing to evaluate and rank the corrosivity of the coagulants. Results from the laboratory scale testing revealed that both coagulants led to localized corrosion of the 5000 and 6000 series aluminum alloys – in the form of pitting, crevice corrosion, and IGC. Therefore, it can be concluded that neither Isopac nor Alum should be used in aeration tanks constructed of the aluminum alloys tested in this study. Whilst the immersion testing did not simulate all conditions observed and measured in the corroded tank, the testing did allow for the study of the isolated, corrosive effects of either Isopac or Alum on the tested alloys. It can be reasoned that even though the coagulants led to similar corrosion observed in the tank, the coagulants themselves are not the sole cause of the aforementioned corrosion; ultimately, additional factors and conditions in the aeration tank could be deemed more corrosive than merely the coagulants.
Language
English
DOI
doi:10.7939/R3CC0V571
Rights
This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for the purpose of private, scholarly or scientific research. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
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