Below the ground, unseen, the backbone of modern civilization is starting to crumble.
From small towns to megacities worldwide, bacteria in wastewater are destroying sewers, pipelines, and treatment plants. The phenomenon, known as microbial-induced corrosion, impacts any community that produces wastewater.
Although there is no standard test method to assess the extent of this corrosion, Oregon State engineers are designing a safer, quicker, more accurate test of products used to prevent it.
“This is a $390 billion problem in the U.S. alone, and it’s a problem everywhere that relies on proper sewage treatment. It’s a global issue,” said Burkan Isgor, professor of infrastructure materials and the John and Jean Loosley Faculty Fellow.
Most major water infrastructure is made of concrete, which is a durable material but is vulnerable to deterioration when it interacts with wastewater.
“Some microbes in wastewater consume waste and produce the gas hydrogen sulfide,” Isgor said. “Other microbes convert this poisonous gas to sulfuric acid, which attacks and damages the concrete.”
Traditionally, industry and governmental organizations have taken two approaches to the problem. One is to topically apply antimicrobial additives to existing concrete structures to fight the bacteria and reduce the occurrence of acid attack. The other is to alter concrete mixture design by adding supplementary materials, such as slag and fly ash, to make the concrete more corrosion resistant.
“The problem is that a test method does not exist to determine how effective these approaches are,” Isgor said. “For example, if a company develops an antimicrobial product, we don’t have a good way of testing whether that product works — or which environment it works in.”
Testing the products in natural environments is technically challenging and not easy to perform in a controlled way. Testing is also risky, because researchers may be exposed to hydrogen sulfide gas. Previous studies by Oregon State researchers have shown that lab tests — where gas, temperature, and moisture are controlled — can be difficult to conduct, cost tens of thousands of dollars per concrete mixture, and take up to 18 months to get results. Additionally, not all labs are equipped to work with a toxic gas.
Another option is to test without bacteria, using a commercially available acid solution, as described in the ASTM C267 Standard. However, this test has challenges. Since the commercial acid is not created biogenically, by bacteria, it cannot be used to test antimicrobial products.
“It’s not a realistic test because the acid is not directly produced by the bacteria,” Isgor said. “The literature has shown a difference between a chemical acid attack and a biogenic acid attack.”
To address this issue, Isgor has collaborated with a team that includes industry partners, such as Concrete Sealants Inc.; the American Concrete Pipe Association; Professor Jason Weiss, head of the School of Civil and Construction Engineering and the Miles Lowell and Margaret Watt Edwards Distinguished Chair in Engineering; and recent graduate Ali Riza Erbektas (’18 M.S., Civil Engineering) to develop an innovative test that alleviates the need for researchers to use toxic gases. Importantly, the test slashes the time needed to produce results to just two months.
“Certain bacteria don’t need the hydrogen sulfide gas to produce the acid,” Isgor said. “We used biosafety level one bacteria and gave them a non-toxic nutrient source and some sulfur compounds, and they produced the acid without the need for the gas. They created the acid attack biogenically.”
Biosafety levels are specified by the Centers for Disease Control and Prevention. Level 1 is the lowest; it does not require specialized protective equipment and allows the test method to be adopted by laboratories easily.
“The testing performed under the guidance of Dr. Jason Weiss and Dr. Burkan Isgor has been instrumental in furthering the understanding of the dynamics of microbial-induced corrosion,” said Howard Wingert, president of Concrete Sealants Inc. “A major problem the industry has suffered is the lack of credible test methods, which accurately evaluate the biological corrosion process and assessment of materials meant to inhibit the process.”
Isgor, Weiss, and Erbektas wrote the new test as a standard, which is in review by the standards-setting organization ASTM International. In addition to the standard, ASTM requested an overview document from the team of Oregon State researchers, which describes microbial-induced corrosion, as a general educational piece for engineering professionals.
“The testing developed at Oregon State has led to a reliable, repeatable testing methodology, which is quickly becoming accepted by the concrete industry,” Wingert said.
“Everyone’s excited about this,” Isgor said. “We hope to have this test available for everyone to use. When you’re creating a standardized test, you want it to be adopted widely and easily.”