Anaerobic production of biosurfactants from contaminated soils: a waste valorization approach to soil remediation

This study investigated the anaerobic production of biosurfactants (BSs) and bioemulsifiers (BEs) by indigenous microbial communities in hydrocarbon-contaminated soils using waste-derived carbon sources as part of a circular economy approach. Sixty microcosms were prepared with real polluted soil, a microemulsion of waste frying oil and chickpea powder, and varying concentrations of nitrate, sulphate, and salinity to explore the influence of environmental conditions on BS/BE biosynthesis under oxygen-limited conditions. Mild oxidative stress was induced by hydrogen peroxide to enhance enzymatic activity. After nine months of incubation, the surface activity of the supernatant was assessed using oil displacement and emulsification index assays, and phytotoxicity was evaluated using germination tests. The results showed that mild salinity and sufficient electron acceptors significantly improved biosurfactant activity, with promising implications for in situ remediation. This low-cost, low-toxicity method valorizes food waste and supports sustainable soil remediation, providing a scalable alternative to synthetic surfactants. Further research is required to optimize production and assess field performance.