A procedure for the selection of the optimal adsorbent for phenolic compounds (PC) recovery from PC-rich wastes and wastewaters was innovatively proposed and applied to compare 4 neutral resins (Amberlite XAD16N, Optipore SD-2, Amberlite FPX66, Amberlite XAD761) and 1 ion-exchange resin (Amberlite IRA958 Cl) for PC recovery from a Tunisian olive mill wastewater (OMW). In the initial batch isotherm tests a neutral resin (XAD16N) performed best thanks to its high PC sorption capacity (81 mgPC/gdry resin) and PC content in the sorbed product (0.19 gPC/gvolatile solids). Also ionexchange resin IRA958, used in OH form in this work, resulted interesting thanks to its satisfactory performances and very low cost (8 €/L). These two pre-selected resins were further compared by means of continuous-flow adsorption/desorption tests conducted in a 1-m packed column. The results indicate that if a low (20%) breakpoint is selected, XAD16N leads to a PC-richer sorbed product (0.14 gPC/gvolatile solids) and a higher operating capacity (0.30) than IRA958. Conversely, if a very high (90%) breakpoint is selected, the two resins produce similar desorbed products in terms of both PC content (0.19-0.21 gPC/gvolatile solids) and antioxidant capacity (4.6-4.9 gascorbic acid equivalent/gPC). Resinspecific dynamic desorption procedures led to very high PC desorption yields (87-95%). The identification of the actual PCs present in the final desorbed product indicated for XAD16N a higher capacity to preserve the integrity of the PC mixture of the studied OMW. OMW microfiltration (0.2 μm pore-size) led to a 99.8% suspended solid removal -thus protecting the packed column from potential clogging -with a very low PC loss.

BACKGROUNDOlive mill wastewater (OMW) represents an environmental problem due to its high organic load and relevant concentration of phenolic compounds (PCs). OMW treatment and disposal represents a relevant challenge and cost for olive mills and multi‐utilities in charge of waste management in Mediterranean countries. The goal of this study was to develop an anaerobic co‐digestion (co‐AD) process of OMW and sewage sludge (SwS) from municipal wastewater treatment.RESULTSDifferent volumetric OMW:SwS ratios up to 100% OMW were fed in continuous 1.7‐L bioreactors. The reactors fed with raw OMW (rOMW) performed better than those fed with OMW dephenolized by adsorption (dOMW). At a 23‐day hydraulic retention time, the best performances were obtained in the reactor fed with 25% rOMW, with a 105% increase in methane yield in comparison to the 100% SwS test. At a 40‐day hydraulic retention time, the reactor fed with 40% rOMW attained a 268 NLCH4/kgvolatile solids methane yield. The conversion of phenolic compoundsreached 70% when the hydraulic retention time was increased from 23 to 40 days. A cost–benefit analysis indicated that both rOMW co‐AD in existing digesters and phenolic compounds recovery from OMW followed by co‐AD of dOMW can lead to relevant additional revenues for the multi‐utilities in charge of wastewater management.CONCLUSIONThis work proves that, using the existing network of SwS anaerobic digesters, it is feasible to co‐digest the entire OMW production in regions characterized by intense olive oil production, thus attaining a relevant increase in methane production yield (a 144% increase in comparison to 100% SwS). © 2020 Society of Chemical Industry (SCI)