The manufacture of olive oil produces large amounts of a dark colored juice called OMW that consists of a mixture of water from the olive, machinery cooling waters, fruit washings, and remainder of the fruit. Typically, OMW comprises about 15 % organic material that is composed of carbohydrates, proteins, and lipids as well as a number of other organic compounds including monoaromatic and polyaromatic molecules [62] and the toxic effects are mainly derived from its extremely high organic load and the presence of recalcitrant organic compounds such as polyphe­nols with strong antimicrobial properties. Hence valorization of OMW produced by the olive oil industry has long been an environmental concern in Mediterranean countries [61]. Beside various conventional technological treatment methods ap­plied, biovalorization of OMW to value-added chemicals is considered as the most cost-effective and environmentally compatible option [73]. Due to its composition with high carbon-to-nitrogen ratio, its use as a suitable substrate for microbial poly­mer production has been proposed [45] and applied to produce pullulan [45] and xanthan gum [74]. By studying the resource variability factors [55] and then by use of a high-producer strain and medium optimization, Lopez et al. [56] reported significant improvements in xanthan yields, reaching 7.7 g/L in 5 days. In all these studies, in order to reduce the inhibitory effect of phenols, the OMW obtained from the industry was clarified by filtration, diluted with distilled water or saline, neu­tralized, sterilized by autoclaving, and then used in microbial fermentation. OMW pretreated by this approach has also been used for the microbial production of a metal-binding EPS by Paenibacillus jamilae bioreactor cultures. Due to the high phenol biodegradation ability of Paenibacillus genus, these cultures were not only proposed for the production of an EPS that could be used as a biofilter but also for the bioremediation of OMW [62]. The main constraint associated with the use of OMW is the need for dilution in order to lower the amount of phenols which in turn limits the concentration of the used waste as culture medium [62]. On the other hand, for the в-glucan production from the fungus Botryosphaeria rhodina DABAC-P82, OMW was only clarified by centrifugation and then after steam sterilization, di­rectly applied as substrate without dilution. Due to the lack of oxidase activity, high biopolymer yields and decreases in phenol content of the culture were attributed to the adsorption action of the fungal biofilm [60]. Undiluted OMW was found to be a poor substrate for pullulan production by A. pullulans [46]. Besides EPSs, OMW has also been used as a fermentation substrate for the microbial production of other biopolymers including polyhydroxyalkanoates (PHAs) [75].