Chemical-biotechnological integrated process for the dephenolization of olive mill wastewater and its acidogenic fermentation in a packed bed biofilm reactor

Polyhydroxyalkanoates (PHAs) are biopolymers whose costs are not competitive with those of fossil fuel-based plastics. The exploitation of organic waste in PHA biotechnological production is of great interest in the perspective of reducing their costs. To this aim, a three-stage integrated anaerobic-aerobic process fed with olive mill wastewaters (OMWs) was proposed (Dionisi et al., 2005). In its first step, the waste is digested under acidogenic conditions in order to obtain a volatile fatty acids (VFAs) enriched effluent to be fed to the following PAH producing aerobic steps. OMW polyphenols, which contribute to the waste phytotoxicity, are natural antioxidants whose exploitation can concern several industrial fields. Thus, an integrated chemical-biotechnological process for the recovery of OMW polyphenols by liquid-solid extraction and for the continuous acidogenic fermentation of the dephenolized waste was developed. The employed OMW (pH = 4.5) had a total phenol content (on Folin-Ciocalteu method basis) of 4.6 g/L, while COD and VFA concentrations were 55 and 8.4 gCOD /L, respectively. As a result of the adsorption pre-treatment, carried out with resin Amberlite XAD16 as the solid phase (0.7 g/L, contact time = 2 hours), the 90% of OMW polyphenols were removed together with the 25% of the COD, while VFA concentration and pH did not vary appreciably. Almost all the adsorbed phenolic fraction was desorbed by using ethanol as the solvent. The resulting wastewater was processed in a biofilm reactor packed with ceramic filters developed in a recent study (Beccari et al., 2009). On the basis of the results obtained from a preliminary batch experiment, the pH of the influent flow was correct to 7.0 and the reactor was thermostated at 25°C and fed with an OLR of about 6 gCOD/L/day. The process effluent, whose pH was 6.2, had a total VFA and COD concentrations of 19.02 and 25.94 gCOD/L, respectively. A significant enhancement in terms of VFA production yield with respect to the former experience (Beccari et al., 2009) was achieved. In particular, butyric and acetic acids were the main detected VFAs in the obtained effluent where they represented the 28 and 27%, respectively, of the whole VFA mixture. Beccari M. et al. (2009) J Chem Technol Biotechnol 84:901-908. Dionisi D. et al. (2005) Wat Res 39:2076-2084.