Research Article Received: 17 June 2012 Revised: 24 August 2012 Accepted: 25 August 2012 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/jctb.3931 Conversions of olive mill wastewater-based media by Saccharomyces cerevisiae through sterile and non-sterile bioprocesses Dimitris Sarris, a Marios Giannakis, a Antonios Philippoussis, b Michael Komaitis, a Apostolis A. Koutinas a and Seraphim Papanikolaou a* Abstract BACKGROUND: Olive mill wastewaters (OMWs) are an important residue and several methods have been proposed for their treatment. RESULTS: Remarkable decolorization (∼63%) and phenol removal (∼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 L -1 (conversion yield per sugar consumed of 0.46 g g -1 ) in a batch bioreactor non-sterilized trial with OMW–glucose enriched medium used as substrate, that presented initial reducing sugars concentration at ∼115 g L -1 . 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 Keywords: Saccharomyces cerevisiae; olive-mill wastewaters; bio-ethanol; waste bioremediation INTRODUCTION Olive mill wastewaters (OMWs) are the principal waste stream deriving from the olive oil production process. These residues are considered to be one of the most difficult-to-treat effluents. 1 Their overall annual production is estimated to be over 3×10 7 m 3 . 2,3 In Greece, the production of this residue is estimated to be up to 1.5×10 6 m 3 . 4 In these wastewaters, BOD and COD values can be 200–400 times higher than those typically met in municipal sewage, with the organic fraction of these materials being composed of sugars, (poly)-phenolic compounds, organic acids and residual oil. 1,2,5,6 OMW composition is variable and depends on several factors such as the variety of olive fruits, the conditions and the technology used for the extraction of oil. 5 – 7 In some cases OMWs derived from press extraction systems, besides phenolic compounds, contain reducing carbohydrates (principally glucose) in very high quantities (i.e. ≥70 g L −1 ) 5 that also pose significant problems related with their treatment. The OMW dark color and phytotoxic and antimicrobial effects have been attributed to the phenolic compounds that are found in various concentrations in the residue, 4,6,8 – 10 the breakdown of which is considered to be the limiting step in OMW treatment by biological means. 1,5,9,11,12 The development of cost-effective OMW treatment technolo- gies remains a priority, since OMWs are in most cases discharged directly into the environment without any other treatment. Several physico-chemical processes have been proposed for OMW treatment, but these methods are limited to small-scale operations. 2,13,14 On the other hand, recent developments indi- cate that OMWs should be considered as a fermentation medium to valorize rather than a waste to discharge, being a potential substrate for various fermentation processes. 5 OMW-based media have been used for the cultivation of molds, prokaryotic microor- ganisms, yeast and yeast-like species leading to the reduction of COD values and phenol compounds degradation and also to the production of added-value compounds. 1,5,9,10,12,15 – 20 The worldwide decrease of petroleum feedstock and the concomitant rise in the price of crude oil have rendered as a ∗ Correspondence to: S. Papanikolaou, Laboratory of Food Microbiology and Biotechnology, Department of Food Science and Technology, Agricultural University of Athens, Iera Odos 75, – Athens, Greece. Email: spapanik@aua.gr a Department of Food Science and Technology, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece b National Agricultural Research Foundation, Institute of Technology of Agricultural Products, Laboratory of Edible Fungi, 1 Sofokli Venizelou street, 14123 Lykovrysi, Greece J Chem Technol Biotechnol (2012) www.soci.org c  2012 Society of Chemical Industry