Using fatty acids for efficient groundwater decontamination

Compounds derived from ammonia, called amines, are used in industrial processes like carbon capture and desalination. However, these often end up as groundwater pollutants and can affect nearby ecology and plant growth.

Pensini et al. sought an efficient way to remove these contaminants. Using a combination of experiments and simulations, the researchers uncovered how fatty acids can help separate and trap pollutants from the water — though short-chain fatty acids can also make certain pollutants more soluble.

For pyridine, one of the toxic amines the group studied, fatty acids compete with the pollutant for hydrogen bond interactions with the water.

“Hydrogen bonds are weak attractions that help water molecules ‘stick’ to each other and also let water interact with many dissolved chemicals,” said author Erica Pensini. “In our mixtures, pyridine and fatty acids both try to interact with water this way, but fatty acids also have an oily tail that water does not like.”

The length of this tail affects an acid’s interaction with pyridine. Short tails prevent pyridine from gathering into large clusters, while long tails disrupt how it mixes with the water, potentially forming a thin film at the water’s surface that can trap the pyridine.

The group was surprised by how much this small parameter affects groundwater pollutants’ effectiveness. By tuning these molecular interactions, they were able to address one of the key challenges in groundwater treatment, the dissolved phase of the pollutants.

“Just changing the fatty acid tail length moved the system away from ‘everything stays mixed’ to ‘pyridine separates into droplets,’ and then further to a self-assembled surface film that can physically trap those droplets — essentially turning a basic interfacial phase transition into a practical, low-energy separation mechanism,” said Pensini.

The researchers are exploring additional factors that may affect groundwater decontamination, including the salinity of the water and the interactions between multiple contaminants.

Source: “Effect of fatty acids on the mixing behaviour of pyridine and diisopropylamine in aqueous mixtures,” by Erica Pensini, Jaime Vickery, Nour Kashlan, Joshua Reed, Alejandro G. Marangoni, Kenneth Truong, and Emanuel Schneck, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0319951 .