Basic Training
Field identification of concrete contaminants commonly encountered in wastewater environments

From JPCL, January 2015

By Vaughn O'Dea, Tnemec Company, Inc.


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Tagged categories: Concrete; Concrete defects; Contaminants; Failure analysis; High-performance coatings; Quality Control; Salt exposure; Wastewater Plants

Comment from Joe Miller, (6/23/2015, 9:47 AM)

Mr. Oday, Your article was very good, concise and lacking just a bit of scope. In the wastewater environments you did not mention microbial contamination. Wastewater environments that have become aenerobic (lacking oxygen) develop colonies of organisms that excrete sulphuric acid, a major contaminant that attacks concrete and linings or coatings. And not just one colony but at least 3. The first colony's excretions lower the pH and create a new environment wherein the next colony can exist. Colony 2 then excretes sulphuric acid at an even lower pH. Once the lower pH level is attained yet a 3rd colony can be spawned to lower the final pH to less than 1. A pH of less than 1 is a very aggressive environment that will attack almost every coating or lining I know of---with devastating results. Of course unlined wastewater structures fare even worse. The detection and measurement of these colonies were found in a study conducted by a P.E. from Purdue and presented at an ACI Conference many years ago. I am sorry I cannot recall his name at the moment but the responses at hi presentation in the room was very loud and angry. Maybe even disbelief? At the time I was working with my R&D and Marketing Team to develop an epoxy lining for manholes. We were also stunned by the realization that a pH of 1 existed in these structures in many places. Basically in the entire USA. Hope this helps.

Comment from Joe Miller, (6/23/2015, 10:06 AM)

Mr. Odea, Sorry for the typo of your name above. I also have a correction. The presenter from Purdue as a Microbiologist not a P.E. I think the presentation was clear and convincing evidence of the limited scope we all have when diagnosing problems. I have very high regard for P.E.'s and Microbiologists. And Coating & Lining Manufacturers and Industrial Painting Contractors. But they MUST become more knowledgeable regarding the complex environments we are dealing with especially in wastewater environments. I hope someone starts a discussion on Potable Water environments next. I have things to add to that one as well. Thanks.

Comment from Vaughn O'Dea, (6/24/2015, 10:02 PM)

Mr. Miller, thank you for your comments. I agree that the deterioration of concrete caused by biogenic sulfide corrosion has been recognized as a serious problem in wastewater collection systems and headworks facilities for the past several decades. The problem of biogenic sulfide concrete corrosion is known in collection systems in most of the world. In some of the worst cases, the lifetime of sewer pipes, manholes and lift stations has been reduced to less than ten years. Sulfide in sewers is formed when sulfate-reducing bacteria (SRB) oxidize organic matter with sulfate or other oxidized sulfur components as electron accepter. The process takes place under anaerobic conditions and is mainly ascribed to the activity of SRB of the genus Desulfovibrio and Desulfobulbus. Hydrogen sulfide and carbon dioxide—both acid gases—are absorbed in the condensate present in sewer headspaces and slowly depress the pH of the surface to around 9. The oxidation of hydrogen sulfide on the concrete surface above the waterline is biological after the pH of the surface has dropped below approximately 9. The sulfur oxidizing bacteria (SOB) Thiothrix, Acidithiobacillus thiooxidans, Thiobacillus denitrificans and Thiomicrospira denitrificans have been identified in sulfide oxidizing biofilms. When hydrogen sulfide is taken up by SOB in the headspace environments it is oxidized to sulfuric acid. The acid reacts with the alkaline components of the concrete, mainly calcium hydroxide and calcium carbonate. The product of this reaction is mainly gypsum, which has little structural strength for which reason the concrete is weakened. Carbonation of the concrete has been found to potentially increase the corrosion rate, possibly caused by elevated levels of carbon dioxide in the sewer gas mixture. A more comprehensive explanation can be found in the November 2007 issue of Materials Performance magazine I authored. Unfortunately, for the January 2015 Basic Training article I was constrained by word count, content, and breadth of discussion to adequately explore this specific subject matter. However, as you astutely pointed out, the corrosion mechanism associated with biogenic corrosion is an acid attack. I may have underplayed the role of sulfuric acid attack by listing other acid contaminants possibly encountered in the collection or treatment processes. Nevertheless, the identification of acid contaminated concrete—whether caused by sulfuric acid or otherwise—is hopefully covered in the article to your satisfaction. Thanks again for your worthwhile comments, which might possibly lead to another Problem Solving Forum topic or JPCL article to better discuss your concerns.

Comment from Joe Miller, (6/25/2015, 8:35 AM)

Mr. Odea, Thank you for your response. You have provided a much better explanation in it of the organisms and what they create. Essentially a very low pH environment that can destroy concrete (and steel) pipes and sewer lines and yes manholes and lift stations. As I recall though they drop the pH down to less than 1 in the final colony stage. What have you in your product line to address such a low pH environment? I am keen to find out. Thanks, Joe Miller

Comment from Vaughn O'Dea, (7/13/2015, 10:27 PM)

Mr. Miller, As covered in my November 2007 Materials Performance article, the pH of the concrete surface can drop below a 1 pH due to reaction with sulfuric acid secreted by the SOB. This low pH will attack concrete, carbon steel, and many types of stainless steels. There are several high-performance protective coatings on the market to protect against severe wastewater exposures, including a line of epoxy technology manufactured by Tnemec. The fundamental protection attribute to these materials is the resistance to hydrogen sulfide, carbon dioxide and methane (sewer gases). It is the permeation of these gases that initially break down protective linings and allow subsequent attack of the substrate by the acid gases and sulfuric acid. Performance in severe sewer environments is assessed in accordance with ASTM G210, Severe Wastewater Analysis Testing Apparatus. Additional resources on this topic can be found on this site at the following links:

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