BACKGROUNDThe olive oil extraction process currently used in Spain and other Mediterranean countries generates large amounts of a semi-solid by-product known as alpeorujo' or two-phase olive mill waste' (TPOMW). Although TPOMW can be a source of valuable compounds, it is mostly dried and burnt to produce energy. This paper, and for the first time, reports the use of TPOMW as the main carbon source for the production of surfactin, a high added value biosurfactant, by Bacillus subtilisDSM 3256. RESULTSBacillus subtilisDSM 3256 was able to grow on TPOMW, the surface tension of the culture medium being reduced to 30.10.9 mN m(-1). FTIR and mass spectrometry determinations confirmed that the biosurfactant produced was surfactin. The highest surfactin concentration was obtained after 36h fermentation, and the product yield from biomass (Y-P/X) was 0.068gg(-1). Part of the phenolic compounds of TPOMW was extracted with the biosurfactant. CONCLUSION: Two-phase olive mill waste can be used as the main carbon source for the production of surfactin. Surfactin yield from biomass was similar to that achieved with other bacterial strains and carbon sources. The biosurfactant was successfully applied to the remediation of sandy soils contaminated with engine oil. (c) 2015 Society of Chemical Industry