Inhibitory effects of industrial olive-oil mill wastewater on biomass production of Scenedesmus obliquus

The three-phase extraction process of olive oil yields highly contaminated wastewater (OMW). This waste is frequently dumped untreated either onto soil or into water sources. The biodegradation of this wastewater by the biomass production of microalgae was studied. The experiments were performed in stirred batch tank reactors on a laboratory scale using Scenedesmus obliquus, microalga tolerant to phenolic compounds. The culture medium was prepared with 2.5%, 5%, 10% and 20% OMW (v/v) in water. The experimental conditions were pH = 7.0, T = 298 K, 350 rpm and aeration 1 (v/v)/min with continuous illumination at an intensity of 298 μE m−2 s−1. Four additional comparative cultures were carried out: (1) 5% OMW without fat matter (WF); (2) 5% OMW pretreated with active carbon (WC); (3) synthetic mineral medium (RL); and (4) urban wastewater from the secondary treatment (UW). The maximum specific growth rates for the different cultures were μm = 0.037 ± 0.003 h−1 (10% OMW), μm = 0.04 ± 0.002 h−1 (WC), μm = 0.049 ± 0.001 h−1 (WF), μm = 0.048 ± 0.0 h−1 (RL) and μm = 0.052 ± 0.012 h−1 (UW). These results indicate that the fat content in the OMW and its dark colour are the main inhibitors factors of the growth of S. obliquus.