Advances in membrane operations for water purification and biophenols recovery/valorization from OMWWs

Recovery of biomolecules from waste represents one of the most important challenges for sustainable resource exploitation. An innovative process design for water recovery and polyphenols encapsulation from olive mill wastewaters (OMWWs) has been investigated combining conventional pressure-driven processes (mi- crofiltration (MF) and nanofiltration (NF)) and relatively new membrane operations (osmotic distillation (OD) and membrane emulsification (ME)). After the removal of suspended solids by an acidification/MF step, OMWWs were processed by NF in order to obtain water from the permeate side and a concentrated polyphenolic solution from the re- tentate side. The NF retentate was dewatered by OD and the concentrated polyphenolic stream was encapsulated in a water-in-oil emulsion by ME. The integrated membrane system resulted efficient in all the operation units. Indeed, relatively high fluxes, with respect to literature data, were obtained in both MF and NF steps (60 and 7 L/m2 h, re- spectively); in addition high polyphenols rejections (%) were measured for the NF membrane. The concentration of the NF retentate by OD produced an enriched fraction of low molecular weight poly- phenols according to a concentration factor of 7. This fraction is formulated by the ME process for the production of a W/O emulsion with an encapsulation efficiency of 90%. According to the process mass balance, related to the treatment of 1000 L of OMWWs, 1463 g of phenolic compounds (85% of the initial phenolic content) and 800 L (80% of the initial volume) of purified water can be recovered, respectively.