Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Mark T. Hernandez

Second Advisor

Norman R. Pace

Third Advisor

JoAnn Silverstein

Fourth Advisor

Yunping Xi

Fifth Advisor

Alina Handorean

Abstract

Microbially induced corrosion of concrete wastewater infrastructure is associated with billions of dollars in rehabilitation costs each year. This phenomenon is caused by sulfur-oxidizing microbial communities that grow on hydrogen sulfide and reduced sulfur compounds in the headspace of wastewater conveyance and treatment structures. The occurrence of corrosion has increased markedly in the past 30 years as a result of industrial wastewater pre-treatment legislation, and will likely continue to increase due to ageing systems, climate change, and (sub)urbanization. Current prevention and treatment technologies are relatively expensive and do not target the causative microbiology.

In response to this widespread problem, the objectives of this thesis were to characterize the spatial and temporal trends in corrosion-associated microbial communities and to develop cost-effective engineering controls to prevent corrosion by inhibiting acidogenic biofilms in situ. Corroded concrete was collected from ten utilities in the United States and from specimens exposed in a manhole for between one and twelve months. Corrosion was found to be most severe in sites with high levels of gaseous hydrogen sulfide and carbon dioxide. These sites were characterized by concrete binder degradation, pore water pH values below 1, and low microbial diversity (less than 10 taxa). Severely corroded concrete was colonized primarily by acidophilic sulfur-oxidizer Acidithiobacillus spp. Early-stage corrosion communities were associated with neutral pore water pH and higher microbial diversity, including neutrophilic sulfur-oxidizers and heterotrophs. Bacterial community succession on exposed concrete specimens was similar to that described by culture-based bacterial models. However, an acidophilic euryarchaeon, Ferroplasma spp., was observed in extreme corrosion communities.

A novel concrete formulation amended with activated carbon impregnated with heavy metals was designed to locally inhibit sulfur-oxidizing activity in response to local pH depression. Treated and untreated specimens were exposed in sanitary manholes for up to a year. Treated samples experienced significantly less corrosion than otherwise identical untreated samples, even though the bacterial community compositions of surface biofilms were similar. This formulation can be manufactured with reused metal from industrial wastes and is expected to be several orders of magnitude cheaper than competing products.

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