About two-phase olive oil washing wastewater simultaneous phenols recovery and treatment by nanofiltration

Olive oil industry is concerned to make the whole production process environmentally friendly, and this includes the treatment of the wastewater produced in the mills. In the present work, concentration and recovery of high-added value compounds (phenolic fraction) from two-phase olive-oil washing wastewater (OOWW) and the simultaneous treatment of the effluent by nanofiltration (NF) with a polymeric membrane was studied. Primarily, different pretreatments upstream the membrane unit were examined, adequating the effluent characteristics, that is, reducing the organic and inorganic concentration without compromising the phenolic content for its ulterior recovery. Among them, centrifugation was the most effective in terms of TSS abatement, no phenolic compounds loss, and subsequent highest EC and COD NF rejection. The availability of the centrifuges in the olive mills already, implying minimization of fix costs and needless of chemicals (flocculants), reinforces the proposed process. Moreover, this pretreatment enhanced the downstream stable membrane flux, up to 64.52 L/hm2, concentrating the feed up to 8.33 times. The obtention of a permeate stream with very good saline quality, COD reduced 86.76% and practically free of phenolic content, thus minimized in its recalcitrant and phytotoxic potential, and a concentrate pool enriched in these high added-value antioxidant compounds (up to 1315.7 mg/L) would allow to counter-balance the economic feasibility of the reclamation process.