A multi-step physicochemical-biotechnological approach for the valorization of olive mill wastewaters

Waste valorization processes carried out through integrated multi-step biorefinery approaches can allow a massive exploitation of the waste organic matter. Olive mill wastewaters (OMWs) are agro-industrial wastes of a high environmental concern. A relevant part of their high COD is typically due to polyphenolic compounds, which are known to be toxic if concentrated to such extents. On the other hands, polyphenols are natural antioxidants of special relevance for several industrial sectors. Therefore, their recovery from OMWs provides the double opportunity to obtain high-added value biomolecules and to reduce the phytotoxicity of the effluent. To such an aim, an effective solid phase extraction process was recently developed [1]. The first aim of the present work was to define a protocol for the recovery and reuse of both the adsorbent (Amberlite XAD16 non-polar resin) and extraction solvent (ethanol), in order to verify the feasibility of a possible process scale-up. Very encouraging results were obtained: ethanol was recovered by means of a rotary evaporator, thus obtaining a concentrated phenolic mixture, whose antioxidant properties were demonstrated via ORAC and DPPH assays; furthermore, after its employment, the resin was washed with a sulphuric acid solution and regenerated: no significant losses of the resin adsorption capabilities were observed after 10 operation cycles. The exploitation of the OMW organic matter was further addressed toward the biotechnological production of biobased chemicals, such as H2 and volatile fatty acids (VFAs), which represent a feasible substrate for aerobic bacteria able to produce and store biopolymers such as polyhydroxyalkanoates (PHAs) [3]. A non conventional anaerobic digestion process carried out under acidogenic conditions for the obtainment of VFAs from dephenolized OMWs was recently developed [4]. The second aim of the present study was a further assessment of that process, with the aim of minimizing the process HRT. At a HRT = 5 days, a stable process capable of an effective bioconversion of the OMW organic matter into VFAs was obtained, with a VFA final concentration of about 19.7 gCOD/L, representing about 83% of the overall effluent COD. References [1] Bertin, L., Ferri, F., Scoma, A., Marchetti, L., Fava, F.: Recovery of high added value natural polyphenols from actual olive mill wastewater through solid phase extraction. Chem. Eng. J. 171, 1287-1293 (2011) [2] Beccari, M., Bertin, L., Dionisi, D., Fava, F., Lampis, S., Majone, M., Valentino, F., Vallini, G., Villano, M.,: Exploiting olive oil mill effluents as a renewable resource for production of biodegradable polymers through a combined anaerobiceaerobic process. J. Chem. Technol. Biotechnol. 84, 901-908 (2009) [3] Scoma, A., Bertin, L., Zanaroli, G., Fraraccio, S., Fava, F.: A physicochemical–biotechnological approach for an integrated valorization of olive mill wastewater. Biores. Technol. 102, 10273-10279 (2011)