Bacterial Film Used to Strengthen Soils

Soil sample collection after 2018 Mesa Wildfire for an erosion study.

Washington State University researchers have used granules made from potato waste bacteria to strengthen soil, offering a new alternative to cement additives that are currently used to shore up soils for building and erosion control.

The researchers added the granules containing a bacterial slime called a biofilm to the soil, allowing a more natural and less carbon-intensive way to strengthen the soils.

Reporting on their work in the journal, Biofilm, the authors include graduate student Faysal Shariq, Haluk Beyenal, professor in the Gene and Linda Voiland School of Chemical Engineering and Bioengineering, and Idil Akin, Colf Distinguished Professor in the Department of Civil and Environmental Engineering.

To strengthen weak soils for road or bridge building, engineers typically add cement, but cement takes a tremendous amount of energy to make, creating large amounts of greenhouse gas emissions. Weak soils are also a problem after wildfires. Once they have been denuded of trees, the soils are often prone to landslides and erosion.

“If we could replace even one percent of the cement used in practice, we could do a lot of good for the environment,” Akin said.

Researchers have tried using microbes to create a cement-like calcite material in soil, but the mixture becomes brittle.

Graduate student Faysal Shariq running strength tests.

In their work, the WSU research team showed that their biofilm granules were able to strengthen soils over a wide range of conditions, whether the soils were dry or wet. The material that they used also has the advantage of being a waste material, Beyenal said. The granules which are a waste product from potato processing plants contain bacteria plus a woven mat made up of molecules called polymers.

The researchers now hope to create a purer biofilm that is more environmentally friendly and doesn’t include the bacteria. They also plan to test the biofilm in soils at a variety of concentrations and eventually in the field.

“When we put something on the slope, we have to consider what we do to the downstream water,” Akin said. “With this product, we can engineer it in a way that it will be environmentally friendly for use on slopes.”

The research was partially funded by the National Science Foundation.

Publication: Ahmad Faysal Shariq, et al., Biofilm addition improves sand strength over a wide range of saturations, Biofilm (2023). DOI: 10.1016/j.bioflm.2021.100050

Original Story Source: Washington State University