# Systematic Map of Chemical and Biological Surfactant Effects on Oxygen Mass Transfer at the Air–Water Interface

## TL;DR

This review explores how surfactants, from human activities, impact oxygen transfer at water surfaces, highlighting gaps in research and the potential of biosurfactants for better water treatment.

## Contribution

The paper provides a systematic map of surfactant effects on oxygen transfer, emphasizing the need for more field studies and comparative assessments of biosurfactants.

## Key findings

- Surfactants generally hinder oxygen transfer, with effects depending on their chemistry and water conditions.
- Most studies focus on chemical surfactants, leaving over 92% of surfactant-water combinations untested.
- Biosurfactants show promise as less harmful alternatives, but more research is needed for real-world applications.

## Abstract

This review summarizes scientific studies from 1963 to 2024 on how chemical and biological surfactants affect oxygen transfer at the air–water interface. Surfactants, which often enter water from human activities, can alter water surfaces and involve the transfer of oxygen, an important aspect of water quality and treatment. We reviewed 54 peer‐reviewed studies and sorted them by surfactant type, water type, and experimental scale. A lot of research has been done on chemical surfactants, but less on biosurfactants. Most of the experiments were conducted in labs, indicating that more field research is needed. There are still more than 92.22% of possible combinations of surfactants and water that have not been tested. Surfactants usually make it harder for oxygen to move through water, but the extent to which they do depends on their chemistry, the amount present, and the water's cleanliness. Research is segregated into distinct disciplines, exhibiting minimal collaboration. This review highlights areas where further research is needed, especially on biosurfactants and their behavior in real‐world water. It also offers ideas for improving wastewater treatment. Our findings support green chemistry and give a framework for better managing oxygen transfer and surfactant pollution in water systems.

Chemical surfactants (e.g., petroleum derivatives) reduce oxygen transfer at the water–air interface via insulating barriers, damaging ecosystems.Biodegradable and less toxic biosurfactants can improve reoxygenation compared to chemicals, making them a viable alternative in contaminated environments.There is a lack of robust comparative assessment between surfactants on oxygen; research in diverse environments is essential for environmental guidelines.

Chemical surfactants (e.g., petroleum derivatives) reduce oxygen transfer at the water–air interface via insulating barriers, damaging ecosystems.

Biodegradable and less toxic biosurfactants can improve reoxygenation compared to chemicals, making them a viable alternative in contaminated environments.

There is a lack of robust comparative assessment between surfactants on oxygen; research in diverse environments is essential for environmental guidelines.

This systematic review confirms that surfactants reduce oxygen transfer (kL/kLa), with concentration and hydrodynamics being critical factors. There was little diversity in the surfactants tested, and aquatic conditions were simplified, and variables (pH, viscosity) were neglected. Future research should test different surfactants, complex waters, and omitted variables for practical applications (WWTPs, industry).