Sustainable Bioremediation Using Cell-Free Broth Containing Rhamnolipid Produced by Pseudomonas Cultivated in Andiroba Biomass Waste from the Brazilian Amazon

The search for sustainable bioremediation technologies is essential to achieve the Sustainable Development Goals. It requires the prospecting of unique environments, such as mining, and the development of low-cost production strategies. This study aimed to isolate biosurfactant-producing bacteria from copper tailings collected at the Salobo mine, Marabá, Pará, to evaluate biosurfactant production and chemical structure using andiroba biomass waste from the Brazilian Amazon as feedstock, and to assess the direct application of the cell-free broth (CFB) for the remediation of metal-contaminated soil. The isolated biosurfactant-producing bacterial AMSD-04 strain was identified as Pseudomonas sp. This bacterium was cultivated using andiroba biomass waste as raw material, achieving a yield of 9.78 g/L of the extracted product and an estimated rhamnolipid-equivalent titer of 15.65 mg/L based on the orcinol rhamnose assay after 12 days of incubation. Chemical characterization indicated that the product is a mixture of rhamnolipid congeners, primarily the di-rhamnolipid. The CFB was applied for the mobilization of total Fe and total Cr from contaminated soil, demonstrating selectivity for total Fe with a maximum metal mobilization capacity of 22.2 mg/kg soil, representing approximately 89% mobilization, compared with 19.5 mg/kg soil (78% mobilization) for total Cr. Kinetic studies revealed a rapid mobilization process where the empirical pseudo-first-order model provided lower non-linear error values (χ2 = 0.060 for total Fe; 0.140 for total Cr) and closer agreement with experimental equilibrium capacities compared to the pseudo-second-order model. These findings indicate that the direct use of CFB from this novel isolate represents a potentially low-cost and bio-based strategy for ex situ laboratory-scale soil washing. This work reinforces the importance of biotechnological processes for generating sustainable bioproducts with industrial applications from agro-industrial and traditional Amazonian waste.