BACKGROUND: Olive mill wastewaters (OMWs) are an important residue and several methods have been proposed for their treatment. RESULTS: Remarkable decolorization (similar to 63%) and phenol removal (similar to 34% w/w) from OMW was achieved. In glucose-based flask sterile cultures, enrichment with OMWs increased ethanol and biomass production compared with cultures without OMWs added. Flask sterile and un-sterilized cultures demonstrated similar kinetic results. Batch-bioreactor trials performed showed higher ethanol and lower biomass quantities compared with the respective shake-flask experiments, while cultures used under un-sterilized conditions revealed equivalent results to the sterile ones. In non-sterile bioreactor cultures, OMWs addition enhanced biomass production in comparison with culture with no OMWs added, whereas ethanol biosynthesis was not affected. The maximum ethanol quantity achieved was 52 g L1 (conversion yield per sugar consumed of 0.46 g g1) in a batch bioreactor non-sterilized trial with OMWglucose enriched medium used as substrate, that presented initial reducing sugars concentration at similar to 115 g L1. Fatty acid analysis of cellular lipids demonstrated that in OMW-based media, cellular lipids containing increased concentrations of oleic and linoleic acid were produced in comparison with cultures with no OMWs added. CONCLUSIONS: S. cerevisiae simultaneously produced bio-ethanol and biomass and detoxified OMWs, under non-sterile conditions. (c) 2012 Society of Chemical Industry